Parameters Affecting the Kidney Size in Individuals without Known Renal Pathology: an Ultrasonographic Study

Background:Renal size can be affected by various causal elements such as age, sex, and demographic characteristics. It is crucial for medical professionals to consider these factors when making clinical decisions. The purpose of this investigation was to establish normograms for renal measurements and explore their association with the anthropometric variables in the natives of Northern India. Methods:A total of 105 individuals with presumed healthy kidneys were enrolled in the present study. Kidney length, width and parenchymal thickness were measured, and data were analysed to identify potential differences related to age, gender and side. Correlation analysis was conducted to examine the relationship between kidney measurements and body biometrics, including body height, body weight, body mass index (BMI) and body surface area (BSA). Results:Mean values for kidney length, width and parenchymal thickness in the 209 kidneys analysed were as follows: right kidney - length 10.65 ± 1.34 cm, width 4.5 ± 0.42 cm and parenchymal thickness 0.91 ± 0.16 cm; left kidney - length 10.7 ± 1.69 cm, width 4.78 ± 1.26 cm and parenchymal thickness 0.76 ± 0.40 cm. Thickness showed significant differences between the right and left kidneys. No significant differences in renal parameters were found between males and females. Analysis based on age groups revealed an increase in renal length and thickness with advancing age, while width decreased in the middle age group (31-40 years) and then increased. Weak positive correlations were observed between kidney parameters and body height, body weight, BSA, and BMI. Conclusion:Renal parameters can vary among different populations depending on age, demographic characteristics, and ethnicity. Therefore, relying on commonly cited values for renal sonographic interpretation or clinical decision-making may not be appropriate. Interpreting renal measurements should be based on reference data specific to the studied population.

Haemodynamics and Arterial Blood Gases in Smokers versus Non Smokers During General Anaesthesia for Abdominal Surgeries: An Analytical Study

Introduction: Tobacco smoking is a worldwide accepted health hazard and its effect on cardiopulmonary system is a wellknown fact. In a long run, it results in to gross derangements in haemodynamics and arterial blood gases which can lead to further complications during general anaesthesia. Aim: To evaluate the effect of smoking on cardiopulmonary system, and also to compare its effects on haemodynamics and arterial blood gases during general anaesthesia for abdominal surgeries in smokers and non smokers. Materials and Methods: This analytical study was conducted in the Department of Anaesthesiology, Mahatma Gandhi Memorial Medical Colledge, Indore, Madhya Pradesh, India, from May 2020 to April 2021. The study included 74 male patients of American Society of Anaesthesiologist (ASA) grade I and II, aged 20-70 years, undergoing elective abdominal surgeries. The patients were divided into two groups, smokers and non smokers, depending on their smoking status. Haemodynamic monitoring was done from preinduction time till 48 hours after extubation, and arterial blood gas analysis was also done before induction and 2 hours after extubation in both the groups. T-test and Mann-whitney test were applied according to the requirement. A p-value < 0.05 was taken as statistically significant. The statistical software Statistical Package for Social Sciences (SPSS) version 20.0 and Medcalc 19.5 were used for the analysis. Results: Significant increase in Heart Rate (HR) and Mean Arterial Pressure (MAP) was observed in smokers as compared to non smokers at all time intervals (p-value<0.001). End-tidal carbon dioxide concentration (EtCO2 ) values were found to be significantly higher in smokers (37.77±2.63 mmHg) than non smokers (32.99±2.83 mmHg) (p-value<0.001). Regarding arterial blood gas analysis significant difference was observed in preoperative and postoperative arterial carbon dioxide concentration (PaCO2 ) (p-value<0.0001), and pH levels (p-value<0.0001) in both the groups. A significant difference was also seen in preoperative and postoperative PaCO2 levels of the smokers (p-value= 0.0004) with a corresponding change in their pH levels also (p-value=0.0012). Peak Expiratory Flow Rate (PEFR) was lower in smokers in comparison to non smokers (p-value<0.0001). Conclusion: Smoking has significant effects on haemodynamic status and arterial blood gases of smokers which can be aggravated during general anaesthesia.

A Comparison of Dexmedetomidine and Fentanyl as Co-induction Agents to Propofol for Insertion of Proseal Laryngeal Mask Airway: A Randomised Clinical Study

Introduction: The Supraglottic Airway Devices (SAD) are bridges between a face mask and Endotracheal Tubes (ETT). Various induction agents like sevoflurane and propofol were used till date for smooth insertion. Propofol causes dose-dependent cardio-respiratory depression while opioids may increase the haemodynamic instability. Aim: To investigate the role of dexmedetomidine and fentanyl as co-induction agents to propofol for Proseal Laryngeal Mask Airway (PLMA) insertion conditions. Materials and Methods: The present study was a randomised clinical study in which 60 patients of American Society of Anaesthesiologists (ASA) grade I-II, 20-60 years of age were divided into two groups. Group P+D received 2.5 mg/kg propofol + 1 µg/kg dexmedetomidine while Group P+F received 2.5 mg/ kg propofol + 1 µg/kg fentanyl. A Bispectral Index (BIS) value of 50-45 was taken as desired end point for insertion of PLMA. Induction time, insertion time, ease of insertion, number of attempts, total propofol requirement and various hemodynamic changes were taken into consideration. Results: Mean induction time with dexmedetomidine (8.28±0.81min) was lower as compared to that with fentanyl (9.28±0.83 min) (p<0.0001). Total propofol requirement was also less with dexmedetomidine (93.66±15.64 mg) as compared to that with fentanyl (135.8±10.95 mg). Dexmedetomidine also provided better insertion score for PLMA (p=0.044) with less number of attempts (p=0.044), when compared with fentanyl. Conclusion: Dexmedetomidine, as an adjuvant to propofol can be considered as an attractive choice for insertion of PLMA.

Comparison of Nalbuphine and Dexmedetomidine versus Nalbuphine and Propofol for Monitored Anaesthesia Care in Tympanoplasty: A Randomised Double-blind Study

Introduction: Tymanoplasty, a middle ear surgery, is done either under Local Anaesthesia (LA), General Anaesthesia (GA) or sedation with local anaesthesia. It is usually performed under Monitored Anesthesia Care (MAC) providing advantages of rapid onset, allowing hearing test intraoperatively and early mobilisation of the patient. Aim: To study the effect of nalbuphine/dexmedetomidine with nalbuphine/propofol on sedation and analgesia in tympanoplasties performed under MAC. Materials and Methods: This randomised, double-blind, clinical study was conducted from June 2020 to June 2021 in the Department of Anaesthesiology at Mahatma Gandhi Memorial Medical College and MY Hospital, Indore, Madhya Pradesh, India. Total 60 adult patients, of American Society of Anesthesiologists (ASA) grade I and II undergoing tympanoplasty under MAC, were randomly allocated into two groups. All patients received injection nalbuphine 50 μg/kg intravenously. Group D received a bolus dose of injection dexmedetomidine 1 μg/kg i.v. over 10 min followed by an infusion at 0.3 μg/kg/h i.v. Group P received a bolus dose of injection propofol 0.75 mg/ kg followed by an infusion at 0.025 mg/kg/min i.v. Sedation and analgesia were titrated to Ramsay Sedation Score (RSS) and Visual Analog Scale (VAS) of 3 each. The vital parameters and need for intraoperative rescue sedation/analgesia were recorded and compared. Results: Mean RSS was significantly more in group D (3.11±0.055) than group P (2.80±0.350). Overall, VAS score was significantly less in group D (1.60±0.670) than group P (2.70±0.691). In group D, 2 (6%) patients and in group P, 4 (12%) patients required inj. midazolam. Similarly, the requirement of inj. paracetamol in group D was in 3 (10%) patients, and in Group P it was 10 (33%) patients. Bradycardia (23.3% in group D and 13.3% in group P) and hypotension (20% in group D and 13.3% in group P) were the major side-effects seen in the study. Conclusion: Nalbuphine/dexmedetomidine is superior to nalbuphine/propofol in producing sedation and decreasing VAS in patients undergoing tympanoplasty under MAC.

Characterization of calcium-mobilizing, purinergic P2Y(2) receptors in human ovarian cancer cells

In human ovarian EFO-21 and EFO-27 carcinoma cells, extracellular ATP induced a concentration-dependent rise in intracellular calcium concentration ([Ca(2+)](i)), suggesting the expression of a purinoreceptor. ATP and UTP were equipotent in generating [Ca(2+)](i) signals, followed by ATP-gamma-S and ADP, whereas beta, gamma-ATP, 2 methyl 1 thio-ATP, 3'-o-(4-benzoyl) benzoyl-ATP, AMP, and adenosine were ineffective. This pharmacological profile suggested the presence of the P2Y(2) subtype in both cell types, and this was confirmed by reverse transcription-polymerase chain reaction (RT-PCR) analysis using P2Y(2) primers. ATP-induced [Ca(2+)](i) signals were composed of two phases: an early and extracellular calcium-independent phase, followed by a sustained plateau phase that was dependent on capacitative calcium influx. In addition to the rise in the [Ca(2+)](i), a time- and concentration-dependent increase in phosphatidylethanol accumulation was observed in ATP-stimulated cells, indicating an increase in phospholipase D activity. RT-PCR analysis identified the expression of a transcript for the phospholipase D-1 subtype of this enzyme. Activation of these receptors by a slowly degradable analogue, ATP-gamma-S, attenuated basal and fetal calf serum-induced cell proliferation in a time- and concentration-dependent manner. These results indicate that ATP may act as an extracellular messenger in controlling the ovarian epithelial cell cycle through P2Y(2) receptors.

Local Regulation of Gonadotroph Function by Pituitary Gonadotropin-Releasing Hormone

Cultured rat pituitary cells and immortalized pituitary gonadotrophs (alphaT3-1 cells) express specific messenger RNA transcripts for GnRH and exhibit positive immunostaining for the GnRH peptide. Each cell type released GnRH during both static culture and perifusion, albeit in lesser amounts than cultured hypothalamic cells and GT1-7 neurons. In perifused pituitary cells, exposure to a GnRH agonist stimulated the release of GnRH as well as LH. In contrast, treatment with a GnRH receptor antagonist or with GnRH antiserum decreased basal LH release. In pituitary cell cultures, a small proportion of gonadotrophs exhibited high amplitude and low frequency baseline Ca2+ oscillations in the absence of GnRH stimulation. Such spontaneous oscillations were comparable to those induced by picomolar concentrations of GnRH and could be abolished by treatment with a GnRH antagonist. These in vitro findings indicate that locally produced GnRH causes low level activation of pituitary GnRH receptors, induces spontaneous intracellular Ca2+ oscillations, and contributes to basal LH secretion in cultured pituitary cells. In vivo, such autocrine or paracrine actions of pituitary-derived GnRH could provide a mechanism for the maintenance of optimal responsiveness of the gonadotrophs to pulses of GnRH arising in the hypothalamus. The presence and actions of GnRH in the anterior pituitary gland, the major site of expression of GnRH receptors, suggest that local regulatory effects of the neuropeptide could supplement the primary hypothalamic mechanism for the control of episodic gonadotropin secretion.

Expression and function of the gonadotropin-releasing hormone receptor are dependent on a conserved apolar amino acid in the third intracellular loop

The coupling of agonist-activated heptahelical receptors to their cognate G proteins is often dependent on the amino-terminal region of the third intracellular loop. Like many G protein-coupled receptors, the gonadotropin-releasing hormone (GnRH) receptor contains an apolar amino acid in this region at a constant distance from conserved Pro and Tyr/Asn residues in the fifth transmembrane domain (TM V). An analysis of the role of this conserved residue (Leu(237)) in GnRH receptor function revealed that the binding affinities of the L237I and L237V mutant receptors were unchanged, but their abilities to mediate GnRH-induced inositol phosphate signaling, G protein coupling, and agonist-induced internalization were significantly impaired. Receptor expression at the cell surface was reduced by replacement of Leu(237) with Val, and abolished by replacement with Ala, Arg, or Asp residues. These results are consistent with molecular modeling of the TM V and VI regions of the GnRH receptor, which predicts that Leu(237) is caged by several apolar amino acids (Ile(233), Ile(234), and Val(240) in TM V, and Leu(262), Leu(265), and Val(269) in TM VI) to form a tight hydrophobic cluster. These findings indicate that the conserved apolar residue (Leu(237)) in the third intracellular loop is an important determinant of GnRH receptor expression and activation, and possibly that of other G protein-coupled receptors.

Influence of a species-specific extracellular amino acid on expression and function of the human gonadotropin-releasing hormone receptor

The mammalian GnRH receptor is an atypical G protein-coupled receptor which lacks the C-terminal cytoplasmic tail that is present in all other seven-transmembrane domain receptors. The mouse and rat GnRH receptors contain 327 amino acids, whereas human, sheep, and bovine receptors have an additional residue in the second extracellular loop at position 191. Another notable species difference is that human receptors undergo agonist-induced internalization much more rapidly than the mouse receptor. In this report, the role of the additional amino acid (Lys191) in GnRH receptor function was studied in transiently expressed mutant and wild-type human and mouse GnRH receptors. Deletion of Lys191 from the human GnRH receptor caused a 4-fold increase in receptor expression in COS-1 and HEK 293 cells and a modest increase in binding affinity. The magnitude of the agonist-induced inositol phosphate response mediated by the deltaK191 human receptor was similar to that of the wild-type receptor, but the EC50 was decreased by about 5-fold. In addition, the rate of internalization of the deltaK191 human receptor was significantly reduced and was similar to that of the mouse receptor. In contrast to these effects of deletion of Lys191, its replacement by Arg, Glu, Gln, or Ala caused no significant change in receptor expression or function. These findings demonstrate that a specific residue in the extracellular region of the human GnRH receptor is a significant determinant of receptor expression, agonist-induced activation, and internalization.

Autocrine regulation of gonadotropin-releasing hormone secretion in cultured hypothalamic neurons

Episodic hormone secretion is a characteristic feature of the hypothalamo-pituitary-gonadal system, in which the profile of gonadotropin release from pituitary gonadotrophs reflects the pulsatile secretory activity of GnRH-producing neurons in the hypothalamus. Pulsatile release of GnRH is also evident in vitro during perifusion of immortalized GnRH neurons (GT1-7 cells) and cultured fetal hypothalamic cells, which continue to produce bioactive GnRH for up to 2 months. Such cultures, as well as hypothalamic tissue from adult rats, express GnRH receptors as evidenced by the presence of high-affinity GnRH binding sites and GnRH receptor transcripts. Furthermore, individual GnRH neurons coexpress GnRH and GnRH receptors as revealed by double immunostaining of hypothalamic cultures. In static cultures of hypothalamic neurons and GT1-7 cells, treatment with the GnRH receptor antagonist, [D-pGlu1, D-Phe2, D-Trp(3,6)]GnRH caused a prominent increase in GnRH release. In perifused hypothalamic cells and GT1-7 cells, treatment with the GnRH receptor agonist, des-Gly10-[D-Ala6]GnRH N-ethylamide, reduced the frequency and increased the amplitude of pulsatile GnRH release, as previously observed in GT1-7 cells. In contrast, exposure to the GnRH antagonist analogs abolished pulsatile secretion and caused a sustained and progressive increase in GnRH release. These findings have demonstrated that GnRH receptors are expressed in hypothalamic GnRH neurons, and that receptor activation is required for pulsatile GnRH release in vitro. The effects of GnRH agonist and antagonist analogs on neuropeptide release are consistent with the operation of an ultrashort-loop autocrine feedback mechanism that exerts both positive and negative actions that are necessary for the integrated control of GnRH secretion from the hypothalamus.

Mediation of cyclic AMP signaling by the first intracellular loop of the gonadotropin-releasing hormone receptor

The gonadotropin-releasing hormone (GnRH) receptor, which is a unique G protein-coupled receptor without a C-terminal cytoplasmic domain, activates both inositol phosphate (InsP) and cAMP signaling responses. The function of the highly basic first intracellular (1i) loop of the GnRH receptor in signal transduction was evaluated by mutating selected residues located in its N and C termini. Replacements of Leu58, Lys59, Gln61, and Lys62 at the N terminus, and Leu73, Ser74, and Leu80 at the C terminus, caused no change in binding affinity. The agonist-induced InsP and cAMP responses of the Q61E and K59Q,K62Q receptors were also unaffected, but the L58A receptor showed a normal InsP response and an 80% decrease in cAMP production. At the C terminus, the InsP response of the L73R receptor was normal, but cAMP production was reduced by 80%. The EC50 for GnRH-induced InsP responses of the S74E and L80A receptors was increased by about one order of magnitude, and the cAMP responses were essentially abolished. These findings indicate that cAMP signaling from the GnRH receptor is dependent on specific residues in the 1i loop that are not essential for activation of the phosphoinositide signaling pathway.

Muscarinic regulation of intracellular signaling and neurosecretion in gonadotropin-releasing hormone neurons

Agonist activation of cholinergic receptors expressed in perifused hypothalamic and immortalized GnRH-producing (GT1-7) cells induced prominent peaks in GnRH release, each followed by a rapid decrease, a transient plateau, and a decline to below basal levels. The complex profile of GnRH release suggested that acetylcholine (ACh) acts through different cholinergic receptor subtypes to exert stimulatory and inhibitory effects on GnRH release. Whereas activation of nicotinic receptors caused a transient increase in GnRH release, activation of muscarinic receptors inhibited basal GnRH release. Nanomolar concentrations of ACh caused dose-dependent inhibition of cAMP production that was prevented by pertussis toxin (PTX), consistent with the activation of a plasma-membrane Gi protein. Micromolar concentrations of ACh also caused an increase in phosphoinositide hydrolysis that was inhibited by the M1 receptor antagonist, pirenzepine. In ACh-treated cells, immunoblot analysis revealed that membrane-associated G(alpha q/11) immunoreactivity was decreased after 5 min but was restored at later times. In contrast, immunoreactive G(alpha i3) was decreased for up to 120 min after ACh treatment. The agonist-induced changes in G protein alpha-subunits liberated during activation of muscarinic receptors were correlated with regulation of their respective transduction pathways. These results indicate that ACh modulates GnRH release from hypothalamic neurons through both M1 and M2 muscarinic receptors. These receptor subtypes are coupled to Gq and Gi proteins that respectively influence the activities of PLC and adenylyl cyclase/ion channels, with consequent effects on neurosecretion.

Mutations of the conserved DRS motif in the second intracellular loop of the gonadotropin-releasing hormone receptor affect expression, activation, and internalization

The GnRH receptor is an unusual member of the G protein-coupled receptor (GPCR) superfamily with several unique features. One of these is a variant of the conserved DRY motif that is located at the junction of the third transmembrane domain and the second intracellular (2i) loop of most GPCRs. In the GnRH receptor, the Tyr residue of the conserved triplet is replaced by Ser, giving a DRS sequence. The aspartate and arginine residues of the triplet are highly conserved in almost all GPCRs. The functional importance of these residues was evaluated in wild type and mutant GnRH receptors expressed in COS-7 cells. Mutants in which Asp138 was replaced by Asn or Glu were poorly expressed, but showed significantly increased internalization and exhibited augmented inositol phosphate generation to maximal agonist stimulation compared with the wild type receptor. In contrast, receptors in which Arg139 was substituted with Gln, Ala, or Ser showed reduced internalization, and the GnRH-induced inositol phosphate response for the Arg139Gln mutant was significantly impaired in proportion to its low expression level. Replacing Ser140 with Ala affected neither internalization nor signal transduction. The role of the polar amino acids at the C terminus of the 2i loop was evaluated in two additional mutants (Ser151Ala, Ser153Ala, and Ser151Ala, Ser153Ala, Lys154Gln, Glu156Gln). Both of these mutants exhibited agonist-induced inositol phosphate responses similar to that of the wild type receptor, but showed increased receptor internalization. This mutational analysis indicates that the conserved Asp and Arg residues in the DRY/S triplet make important contributions to the structural integrity of the receptor and influence receptor expression, agonist-induced activation, and internalization.

Structural organization and characterization of the promoter region of the rat gonadotropin-releasing hormone receptor gene

The gene encoding the rat gonadotropin-releasing hormone (GnRH) receptor was isolated, and its structural organization and promoter region were characterized. The gene was found to consist of three exons that encode the receptor protein, and spanned about 20 kb. Of two genomic clones analyzed, one contained the 5'-untranslated region and the first exon, and the other contained the second and third exons. The sizes of the first, second, and third exons are 625, 217, and 1476 nt, respectively. The first intron is at least 12 kb in length and is located between nucleotides 522 and 523 of the cDNA reading frame, in the middle of the fourth transmembrane domain. The second intron is about 2.5 kb and is also located in the reading frame between nucleotides 739 and 740, separating the fifth and sixth transmembrane domains. Genomic blots in combination with cloning and sequencing suggested that a single GnRH receptor gene is present in the rat genome. Primer extension indicated that the transcription start site is located 103 nt upstream of the translational start codon. A putative TATA box is positioned 23 nt in front of the transcription initiation site. The 1.8 kb 5' flanking sequence contains an SF-1 site, an AP-1 site, CCAAT sequences, a Pit-1 binding site, and a potential CRE-like sequence. To evaluate promoter activity, the 1.8 kb and two 5' deleted fragments of 1.2 and 0.6 kb were fused to the luciferase reporter gene and transiently expressed in immortalized pituitary gonadotrophs (alphaT3-1 cells) and hypothalamic neurons (GT1-7 cells), and in nonpituitary (COS-7) cells. Luciferase gene expression was significantly increased by all three fragments in pituitary and hypothalamic cells, but not in COS-7 cells. The promoter activity of the 1.2 kb fragment was higher than that of the other fragments. Forskolin and cAMP analogs increased luciferase gene expression in both alphaT3-1 and GT1-7 cells, but activation of protein kinase C by phorbol myristate acetate had no effect. These studies indicate that positive and negative regulatory elements are present within the 1.8 kb 5' flanking sequence of the GnRH receptor. Knowledge of the genomic organization and analysis of the promoter region of the rat GnRH receptor gene will facilitate the elucidation of its transcriptional control in pituitary gonadotrophs and hypothalamic neurons.

Dependence of agonist activation on an aromatic moiety in the DPLIY motif of the gonadotropin-releasing hormone receptor

In the GnRH receptor, the NPX2-3Y motif that is present in the seventh transmembrane helix of most G protein-coupled receptors is unusual in containing Asp instead of Asn but retains the highly conserved Tyr residue. The importance of this aromatic residue in the DPLIY sequence of the GnRH receptor function was analyzed by replacing Tyr322 with Ala or Phe residues. The Y322A mutant receptor expressed in COS-7 cells had high agonist binding affinity, but its ability to interact with G protein(s) and to activate inositol phosphate production in response to GnRH was abolished. Although functionally inactive, the Y322A mutant receptor was internalized at about 50% of the rate of the wild type receptor in agonist-treated cells. When Tyr322 was replaced with Phe to preserve its aromatic nature, the Y322F mutant receptor displayed normal G protein activation and inositol phosphate responses to GnRH and was internalized in the same manner as the wild type receptor. These findings demonstrate that the aromatic moiety of the Tyr322 component of the DPLIY motif in the GnRH receptor is a critical determinant of agonist-induced receptor activation and signal transduction.

Effects of second intracellular loop mutations on signal transduction and internalization of the gonadotropin-releasing hormone receptor

The gonadotropin-releasing hormone (GnRH) receptor belongs to the superfamily of heptahelical G protein coupled receptors, most of which have a highly conserved DRYXXV/IXXPL sequence in the second intracellular (2i) loop that has been implicated in G protein coupling. The predicted 2i loop of the GnRH receptor contains serine rather than tyrosine in the DRY sequence but retains the conserved hydrophobic Leu residue, which is required for G protein coupling and internalization of muscarinic receptors. The present study examined the effects of mutating the unique Ser140 to the conserved Tyr, and the conserved Leu147 to Ala or Asp, on agonist binding, internalization, and signal transduction. The S140Y mutant showed a 100% increase in agonist binding affinity, and its internalization was increased by 60% above that of the wild-type receptor. The binding characteristics of the Leu147 mutants were indistinguishable from those of the wild-type receptor, but their internalization was reduced by about 50%. The L147A and L147D mutants also showed significant impairment of GnRH-stimulated inositol phosphate production. These findings demonstrate that substitution of Ser140 by Tyr does not affect G protein coupling but significantly increases receptor affinity and internalization rate. In contrast, replacement of a conserved aliphatic residue (Leu147) impairs both G protein coupling and agonist-induced receptor internalization.

Glucokinase of Escherichia coli: induction in response to the stress of overexpressing foreign proteins

A variety of stressful conditions, such as heat shock, ethanol, osmotic shock, glucose deprivation, and oxidative stress, are known to induce the synthesis of specific proteins. Here, we report the induction in Escherichia coli of a protein elicited in response to a hitherto unidentified stress condition, i.e., the overexpression of foreign proteins. The induced protein identified as glucokinase (EC 2.7.1.2) is produced at a level > or = 20-fold higher than the level in wild-type E. coli when foreign proteins are expressed under the control of the alkaline phosphatase (phoA) promoter. The bacterial glucokinase is shown to have a mass of approximately 47 kDa determined by a "renaturation activity stain assay" in situ following sodium dodecyl sulfate-poly-acrylamide gel electrophoresis and exhibits a high specificity for the phosphorylation of glucose. The apparent Km values for glucose and ATP for the enzyme are 0.15 and 0.50 mM, respectively, indicating that the E. coli enzyme is a low Km glucose hexokinase. The enzyme cross-reacts with rabbit antisera raised against hexokinase from higher eukaryotes, implicating some sequence similarity with mammalian hexokinases. Under normal conditions, E. coli glucokinase plays a minor role in glucose metabolism. However, under anabolic stress conditions, this glycolytic enzyme may be required to supplement levels of glucose 6-phosphate. Alternatively, glucokinase, which is predicted in analogy to other hexose-utilizing kinases to have structural folds characteristic of hsp 70, may itself, or in combination with other E. coli proteins, function in the stabilization of newly synthesized proteins.

Homologous down-regulation of gonadotropin-releasing hormone receptor sites and messenger ribonucleic acid transcripts in alpha T3-1 cells

GnRH is known to down-regulate its pituitary receptors by mechanisms that include endocytosis of the agonist-receptor complex. To evaluate the extent to which changes in receptor synthesis contribute to this process, the effects of GnRH and its analogs on GnRH receptor number and messenger RNA (mRNA) levels were analyzed in the alpha T3-1 gonadotroph cell line. Treatment with GnRH or its potent agonist analog, des-Gly10-[D-Ala6]GnRH N-ethylamide, reduced GnRH receptor number in a time- and dose-dependent manner, with a half-maximal decrease in response to 10(-6) M GnRH or agonist analog by 75 min. The maximum decrease in receptor number (to 31% of the control value) was sustained for up to 72 h. In alpha T3-1 cells incubated with 10(-8) M GnRH or agonist analog, the GnRH receptors fell by 28% and 46% after 2 h, respectively; no change in receptors occurred after treatment with 10(-8) M GnRH antagonist ([D-pGlu1,D-Phe2,D-Trp3,6]GnRH). Time- and dose-dependent reductions in the level of receptor mRNA were also observed after treatment of alpha T3-1 cells with GnRH and the agonist analog. However, the maximal reduction in mRNA levels (to 60-70% of the control value) was consistently less than the decline in receptor number. These results indicate that the mechanism of GnRH receptor down-regulation in alpha T3-1 gonadotrophs includes reduction of receptor synthesis secondary to decreases in receptor mRNA levels. The finding that reductions in mRNA levels were relatively less than the decreases in receptor number is consistent with the involvement of additional mechanisms, including endocytosis and degradation, in down-regulation of the GnRH receptor.

Structure/function relationships in hexokinase. Site-directed mutational analyses and characterization of overexpressed fragments implicate different functions for the N- and C-terminal halves of the enzyme

Hexokinases are comprised of two highly homologous approximately 50-kDa halves and are product-inhibited by glucose-6-P. Four amino acid residues, Ser603, Asp657, Glu708, and Glu742, located in the C-terminal half of the tumor mitochondrial enzyme have been shown to be essential for enzyme function (Arora, K. K., Filburn, C. R., and Pedersen, P. L. (1991) J. Biol. Chem. 266, 5359-5362). Here we have assessed also the role of the N-terminal half of the same enzyme. Site-directed mutagenesis of residues predicted to interact with glucose in the N-terminal half, i.e. Ser155, Asp209, and Glu260, to Ala, have no effect on hexokinase activity. In addition, inhibition by hexose mono- and bisphosphates is unchanged for each of the mutant enzymes. Significantly, the overexpressed N-terminal polypeptide is devoid of catalytic activity but does have the capacity to bind ATP-agarose and be released with ATP and glucose-6-P. In contrast, the overexpressed C-terminal polypeptide is catalytically active and shows the same product inhibition pattern as the complete 100-kDa parent enzyme. These results emphasize that the N-terminal half of tumor hexokinase is essential neither for catalysis nor product modulation. Rather, the N-terminal half may play another role, perhaps in modulation of the ATP/glucose-6-P-dependent binding of the enzyme to tumor mitochondria or by acting as a spacer between the outer mitochondrial membrane and the C-terminal catalytic unit.

Exchange reactions catalyzed by group-transferring enzymes oppose the quantitation and the unravelling of the identify of the pentose pathway

1. The distributions and rates of transfer of carbon isotopes from a selection of specifically labelled ketosugar-phosphate substrates by exchange reactions catalyzed by the pentose and photosynthetic carbon-reduction-pathway group-transferring enzymes transketolase, transaldolase and aldolase have been measured using 13C-NMR spectroscopy. 2. The rates of these exchange reactions were 5, 4 and 1.5 mumol min-1 mg-1 for transketolase exchange, transaldolase exchange and aldolase exchange, respectively. 3. A comparison of the exchange capacities contributed by the activities of these enzymes in three in vitro liver preparations with the maximum non-oxidative pentose pathway flux rates of the preparations shows that transketolase and aldolase exchanges exceeded flux by 9-19 times in liver cytosol and acetone powder enzyme preparations and by 5 times in hepatocytes. Transaldolase was less effective in the comparison of exchange versus flux rates: transaldolase exchange exceeded flux by 1.6 and 5 in catalysis by liver cytosol and acetone powder preparations, respectively, but was only 0.6 times the flux in hepatocytes. 4. Values of group enzyme exchange and pathway flux rates in the above three preparations are important because of the feature role of liver and of these particular preparations in the establishment, elucidation and measurement of a proposed reaction scheme for the fat-cell-type pentose pathway in biochemistry. 5. It is the claim of this paper that the excess of exchange rate activity (particularly transketolase exchange) over pathway flux will overturn attempts to unravel, using isotopically labelled sugar substrates, the identity, reaction sequence and quantitative contribution of the pentose pathway to glucose metabolism. 6. The transketolase exchange reactions relative to the pentose pathway flux rates in normal, regenerating and foetal liver, Morris hepatomas, mammary carcinoma, melanoma, colonic epithelium, spinach chloroplasts and epididymal fat tissue show that transketolase exchange may exceed flux in these tissues by factors ranging over 5-600 times. 7. The confusion of pentose pathway theory by the effects of transketolase exchange action is illustrated by the 13C-NMR spectrum of the hexose 6-phosphate products of ribose 5-phosphate dissimilation, formed after 30 min of liver enzyme action, and shows 13C-labelling in carbons 1 and 3 of glucose 6-phosphate with ratios which range over 2.1-6.4 rather than the mandatory value of 2 which is imposed by the theoretical mechanism of the pathway.

Hexokinase receptors: preferential enzyme binding in normal cells to nonmitochondrial sites and in transformed cells to mitochondrial sites

Hexokinase plays an important role in normal glucose-utilizing tissues like brain and kidney, and an even more important role in highly malignant cancer cells where it is markedly overexpressed. In both cell types, normal and transformed, a significant portion of the total hexokinase activity is bound to particulate material that sediments upon differential centrifugation with the crude "mitochondrial" fraction. In the case of brain, particulate binding may constitute most of the total hexokinase activity of the cell, and in highly malignant tumor cells as much as 80 percent of the total. When a variety of techniques are rigorously applied to better define the particulate location of hexokinase within the crude "mitochondrial fraction," a striking difference is observed between the distribution of hexokinase in normal and transformed cells. Significantly, particulate hexokinase found in rat brain, kidney, or liver consistently distributes with nonmitochondrial membrane markers whereas the particulate hexokinase of highly glycolytic hepatoma cells distributes with outer mitochondrial membrane markers. These studies indicate that within normal tissues hexokinase binds preferentially to nonmitochondrial receptor sites but upon transformation of such cells to yield poorly differentiated, highly malignant tumors, the overexpressed enzyme binds preferentially to outer mitochondrial membrane receptors. These studies, taken together with the well-known observation that, once solubilized, the particulate hexokinase from a normal tissue can bind to isolated mitochondria, are consistent with the presence in normal tissues of at least two different types of particulate receptors for hexokinase with different subcellular locations. A model which explains this unique transformation-dependent shift in the intracellular location of hexokinase is proposed.

Glucose phosphorylation. Site-directed mutations which impair the catalytic function of hexokinase

Recent studies from this and other laboratories have resulted in the cloning and sequencing of hexokinases from a variety of tissues including yeast, human kidney, rat brain, rat liver, and mouse hepatoma. Significantly, studies on the hepatoma enzyme conducted in this laboratory (Arora, K.K., Fanciulli, M., and Pedersen, P.L. (1990) J. Biol. Chem. 265, 6481-6488) resulted also in its overexpression in Escherichia coli in active form. We have now used site-directed mutagenesis for the first time in studies of hexokinase to evaluate the role of amino acid residues predicted to interact with either glucose or ATP. Four amino acid residues (Ser-603, Asp-657, Glu-708, and Glu-742) believed to interact with glucose were mutated to alanine or glycine, whereas a lysine residue (Lys-558) thought to be directly involved in binding ATP was mutated to either methionine or arginine. Of all the mutations in residues believed to interact with glucose, the Asp-657----Ala mutation is the most profound, reducing the hexokinase activity to a level less than 1% of the wild type. The relative Vmax values for Ser-603----Ala, Glu-708----Ala, and Glu-742----Ala enzymes are 6, 10, and 6.5%, respectively, of the wild-type enzyme. Glu-708 and Glu-742 mutations increase the apparent Km for glucose 50- and 14-fold, respectively, while the Ser-603----Ala mutation decreases the apparent Km for glucose 5-fold. At the putative ATP binding site, the relative Vmax for Lys-558----Arg and Lys-558----Met enzymes are 70 and 29%, respectively, of the wild-type enzyme with no changes in the apparent Km for glucose. No changes were observed in the apparent Km for ATP with any mutation. These results support the view that all 4 residues predicted to interact with glucose from earlier x-ray studies may play a role in binding and/or catalysis. The Asp-657 and Ser-603 residues may be involved in both, while Glu-708 and Glu-742 clearly contribute to binding but are not essential for catalysis. In contrast, Lys-558 appears to be essential neither for binding nor catalysis.

Glucose phosphorylation in tumor cells. Cloning, sequencing, and overexpression in active form of a full-length cDNA encoding a mitochondrial bindable form of hexokinase

In rapidly growing tumor cells exhibiting high glucose catabolic rates, the enzyme hexokinase is markedly elevated and bound in large amounts (50-80% of the total cell activity) to the outer mitochondrial membrane (Arora, K.K., and Pedersen, P.L. (1988) J. Biol. Chem. 263, 17422-17428; Parry, D.M., and Pedersen, P.L. (1983) J. Biol. Chem. 258, 10904-10912). In extending these studies, we have isolated a cDNA clone of hexokinase from a lambda gt11 library of the highly glycolytic, c37 mouse hepatoma cell line. This clone, comprising 4,198 base pairs, contains a single open reading frame of 2,754 nucleotides which encode a 918-amino acid hexokinase with a mass of 102,272 daltons. This enzyme exhibits, respectively, 68 and 32 amino acid differences, including several charge differences, from the recently sequenced human kidney and rat brain enzymes. The putative glucose and ATP binding domains present in the latter two enzymes and in rat liver glucokinase are conserved in the tumor enzyme. At its N-terminal region, tumor hexokinase has a 12-amino acid hydrophobic stretch which is present in the rat brain enzyme but absent in the rat liver glucokinase, a cytoplasmic enzyme. The mature tumor hexokinase protein has been overexpressed in active form in Escherichia coli and purified 9-fold. The overexpressed enzyme binds to rat liver mitochondria in the presence of MgCl2. This is the first report describing the cloning and sequencing of a tumor hexokinase, and the first report documenting the overexpression of any hexokinase type in E. coli. Questions pertinent to the enzyme's mechanism, regulation, binding to mitochondria, and its marked elevation in tumor cells can now be addressed.

Glucose phosphorylation. Interaction of a 50-amino acid peptide of yeast hexokinase with trinitrophenyl ATP

A 50-amino acid peptide predicted by chemical modification studies of yeast hexokinase to contain an ATP-binding site has been synthesized and purified. The peptide, which includes residues from glutamate 78 at the NH2-terminal end to leucine 127 at the COOH-terminal, resides within the smaller of the two lobes found in the three-dimensional structure of yeast hexokinase. It is this region which has been reported recently to exhibit significant sequence homology with hexokinase types I and IV of higher eukaryotic cells and sequence homology with the active site of protein kinases. Similar to native yeast hexokinase, the 50-amino acid peptide interacts strongly with the fluorescent analog TNP-ATP [2',(3')-O-(2,4,6-trinitrophenyl)-adenosine-5'-triphosphate]. A 5-fold enhancement is observed when 8 microM peptide interacts with 20 microM TNP-ATP. The stoichiometry of binding is very close to 1 mol of TNP-ATP/mol peptide. Also, similar to native yeast hexokinase, the fluorescent enhancement observed upon TNP-ATP binding to the synthetic peptide is greater than that observed upon TNP-ADP binding. Finally, TNP-AMP exhibits a much lower fluorescent enhancement in the presence of hexokinase or the synthetic peptide. The additional findings that ATP can readily prevent TNP-ATP binding and that TNP-ATP can substitute for ATP as a weak substrate for hexokinase in the phosphorylation of glucose indicate that the synthetic peptide described here comprises part of the catalytic site.

Functional significance of mitochondrial bound hexokinase in tumor cell metabolism. Evidence for preferential phosphorylation of glucose by intramitochondrially generated ATP

Previous studies from this laboratory have shown that mitochondrial bound hexokinase is markedly elevated in highly glycolytic hepatoma cells (Parry, D. M., and Pedersen, P.L. (1983) J. Biol. Chem. 258, 10904-10912). A pore-forming protein, porin, within the outer membrane appears to comprise at least part of the receptor site (Nakashima, R.A., Mangan, P.S., Colombini, M., and Pedersen, P.L. (1986). Biochemistry 25, 1015-1021). In studies reported here experiments were carried out to assess the functional significance of mitochondrial bound tumor hexokinase. Two approaches were used to determine whether the bound enzyme has preferred access to mitochondrially generated ATP relative to cytosolic ATP. The first approach compared the time course of glucose 6-phosphate formation by AS-30D hepatoma mitochondria under conditions where ATP was regenerated endogenously via oxidative phosphorylation or exogenously by added pyruvate kinase and phosphoenolpyruvate. The second approach involved the measurement of the specific radioactivity of glucose 6-phosphate formed following the addition of [gamma-32P]ATP to either phosphorylating or nonphosphorylating AS-30D mitochondria. Both approaches provided results which show that the source of ATP for bound hexokinase is derived preferentially from the ATP synthase residing within the inner mitochondrial membrane compartment rather than from the medium (i.e. from the cytosolic compartment). These results provide the first direct demonstration that the exceptionally high level of hexokinase bound to mitochondria of highly glycolytic tumor cells has preferred access to mitochondrially generated ATP, a finding that may have rather profound metabolic significance for such tumors.

Rapid methods for the high yield synthesis of carbon-13 enriched intermediates of the pentose-phosphate pathway

Methods for the synthesis of carbon-13 enriched substrates, intermediates and products of the pentose-phosphate pathway, viz. ribose, arabinose, xylulose and ribulose 5-phosphates, sedoheptulose mono- and bisphosphates, octulose (both the ido- and altro-epimers) mono- and bisphosphates, are described. The procedure of the classical Kiliani synthesis was adopted for the preparation of the two starting compounds, [1-13C]ribose and [1-13C]arabinose 5-phosphates. Using these initial reactants and enzymic methods involving the group-transferring enzymes, transketolase, aldolase and transaldolase, a variety of specifically 13C-labelled five-, six-, seven- and eight-carbon sugar phosphates were synthesized in high yield and purity. The isolation and authenticity of each of the 13C-labelled sugars were established by column, paper and thin layer chromatographic methods and specific enzymic assays. The purity and positional isotopic analysis of these sugar-P's were confirmed by 13C-NMR spectroscopy. These specifically 13C-enriched compounds are required for enzymatic, mechanistic and quantitative investigations of pentose-pathway reactions in animal, plant and tumour tissues in vitro and in vivo.

Introduction and metabolism of pentose and hexose phosphates in permeabilized Morris hepatoma 5123TC cells

Metabolism of arabinose 5-P, ribose 5-P and glucose 6-P in permeabilized and resealed Morris hepatoma 5123TC cells was investigated by measuring the contribution of these compounds to nucleic acid biosynthesis. The level of [14C]-arabinose (non-phosphorylated) incorporation into nucleic acids was slight, presumably due to the low activity of the transport system or the absence or low activity of a specific 'kinase' enzyme. The permeabilizing procedure involved the brief treatment of Morris hepatoma 5123TC cells with lysolecithin and resulted in a cell population which was permeable to charged compounds i.e. sugar phosphates and nucleotides, that otherwise could not cross the plasma membrane. The permeabilized (and resealed cells) retained normal cellular morphology and intactness of specific organelles as judged by the maintenance of functional properties. Following permeabilization, these cells resealed when transferred back to normal growth medium, and continued to divide and increase at the same rates as control non-permeabilized cell cultures. The permeabilized cells incorporated deoxyribonucleotides ([methyl -3H]-TTP) into DNA at a linear rate of 0.047 nmol per 10(7) cells min-1, representing 90-100 per cent of the DNA synthesis rate in vivo. The permeabilization technique, when coupled with procedures to establish cell synchrony, permitted the comparative estimate of the contributions of [14C]-labelled arabinose 5-P, ribose 5-P and glucose 6-P to RNA, DNA, amino acids, CO2, lactate and sugar mono- and bisphosphates. The percentage of [14C]-isotope incorporated into total nucleic acids by these three labelled sugar phosphates were 2.3, 4.9 and 6.3 respectively. Possible reasons for the lower incorporation of 14C from arabinose 5-P are given. The results are consistent with the proposal that arabinose 5-P, an intermediate of the L-type pentose pathway activity of 5123TC cells, was incorporated into nucleic acids by its interconversion with ribulose 5-P and ribose 5-P and thus into PRPP. This study represents the first report of sugar phosphate as opposed to free sugar metabolism by tumour cells in culture.

Mechanism and quantitative contribution of the pentose pathway to the glucose metabolism of Morris hepatoma 5123C

An investigation of the mechanism and quantitative contribution of the pentose phosphate pathway in the glucose metabolism of Morris Hepatoma 5123C is reported. Morris Hepatoma 5123C has an active non-oxidative segment of pentose pathway as judged by its ability to convert ribose 5-P to hexose 6-P in a standard assay. Based on compliance with qualitative and quantitative criteria, the cells exhibit the L-type pentose pathway reaction sequence rather than the F-type pathway. This compliance included the formation of intermediates characteristic of the L-type pathway, namely arabinose 5-P, octulose mono- and bisphosphates and sedoheptulose 1,7-bisphosphate, during the dissimilation of ribose 5-P to hexose 6-P. The intermediary role of arabinose 5-P was suggested by the incorporation of its carbon into various intermediates and products of the pentose pathway. Intermediary roles for ido octulose mono- and bisphosphates were supported by their participation in the reaction catalyzed by the phosphotransferase enzyme of the L-type pentose pathway. Presence of L-type PP reactions was further affirmed by 14C-prediction labelling experiments using [5-14C]- and [2-14C]glucose as specifically labelled substrates. Using two methods of measurement, the F-type pentose cycle made a negligibly small contribution to glucose metabolism, while the measured value of the L-type pentose pathway accounted for 30% (approx.) of the total glucose metabolism of these cells, a value consistent with the high activity of the enzymes of the L-type pentose pathway in Morris Hepatoma 5123C cells and the very high activity of the non-oxidative segment of the pathway in vitro. The findings validate the proposal that the L-type pentose pathway reactions constitute the non-oxidative segment of the pathway in Morris Hepatoma 5123C cells. Reasons involving pyruvate recycling reactions show why there is low incorporation of 14C-isotope in C-1 of glucose 6-P, when [4,5,6-14C]glucose and [6-14C]glucose are L-type PP test substrates in intact cells.

"Pyruvate recycling" and its influence on the estimation of the pentose pathway in intact liver and Morris hepatoma 5123TC cells

The phenomenon of "pyruvate recycling" is demonstrated in perfused rat liver, rabbit liver in situ and in Morris Hepatoma 5123TC cells and quantitatively measured using [2-14C]pyruvate and the method of Friedmann et al. (1971). Various metabolites, viz. lactate, DHAP, glucose, glucose 6-P and fructose 6-P were isolated and degraded following the metabolism of [2-14C]pyruvate and [2-14C]glycerol in order to assess the 14C-distributions imparted by "pyruvate recycling" reactions. The labelling of DHAP, lactate, glucose and glucose 6-P showed 14C randomizations consistent with the operation and the quantitative extent of "pyruvate recycling". These findings support the proposal that the actions of "pyruvate recycling" may account for the failure to find significant levels of 14C isotope at C-1 of glucose 6-P following the metabolism of [4,5,6-14C]- or [6-14C]glucose by L-type pentose pathway metabolism in aerobic intact tissues. "Pyruvate recycling" diminishes the measured value of the L-type pentose cycle in intact tissues and qualifies one of the mechanistic predictions of the L-type pentose pathway which was unravelled by tracing its reactions with labelled ribose 5-P and liver enzymes (Horecker et al., 1954; Williams et al., 1978a,b) in vitro. The demonstration of an association of L-type pentose pathway reactions with "pyruvate recycling" by way of the common reactions of their triose-P intermediates qualifies the superficial acceptance of the predictions of the L-type pathway in vitro for the distribution of isotopic labels by aerobic tissues in vivo.

The metabolic significance of pentose cycle measurements in perfused liver

The controversial dissension concerning the nature of the pentose cycle in liver is investigated. The metabolism of [2-14C]Glc and [1-14C]Rib in chronically perfused normal and regenerating rabbit liver and acutely perfused rat liver are used to test the mechanistic predictions and contribution of the F-type pentose cycle. 14C was traced in Glc, Glc 6-P, Fru 6-P, glycogen and Rib 5-P. None of the data complied with the critical theoretical limits set for the C-1/C-3 ratio (the identity badge of the F-type pentose cycle or pathway) for all values of F-type PC from 0-100%. Thus apparent F-type PC measurements using the Katz & Wood method gave a wide scatter of calculated values. The 14C distributions in Rib 5-P do not conform with the predictions of the F-type PC but are in agreement with the many previous results of similar experiments reported by Hiatt and co-workers. In perfused rat liver the C-1/C-3 constants in Glc 6-P and glycogen also failed to conform with F-PC theory following the metabolism of [2-14C]Glc. The metabolism of [5-14C]Glc and distribution of 14C in Glc 6-P and glycogen showed that L-type PC was 18%, in close agreement with a previous published value of 22% for rat hepatocytes. Metabolism of [6-14C]Glc and [4-14C]Glc (as [4,5,6-14C]Glc) showed that Pyruvate Recycling was active in perfused rat liver. None of the data from these comprehensive investigations can confirm the results of the recent study reported by the Landau laboratory on the pentose pathway metabolism of Glc and Rib in perfused rat liver.

The significance of sedoheptulose 1,7-bisphosphate in the metabolism and regulation of the pentose pathway in liver

Rat liver cytosolic enzyme preparation catalyses the formation of sedoheptulose 1,7-P2 (60% of total heptulose-P formed) from hexose 6-P and triose 3-P (reverse mode of pentose pathway operation). Smaller amounts of sedoheptulose 1,7-P2 are also formed from ribose 5-P during the non-oxidative synthesis of hexose 6-P (forward pentose pathway operation). The apparent absence of erythrose 4-P in biological systems may be explained by its contribution to carbons 4,5,6 and 7 of sedoheptulose 1,7-P2 as well as its pronounced ability to exist in dimeric form. Apart from the aldolase catalyzed formation of sedoheptulose 1,7-P2, 6-phosphofructokinase also catalyses its formation from sedoheptulose 7-P and fructose 1,6-bisphosphatase catalyses its dephosphorylation. These three enzymes may contribute to the regulation of carbon flux through the near equilibrium reactions of the non-oxidative pentose phosphate pathway in vivo. The phosphotransferase enzyme of the L-type pentose pathway is also able to catalyse the interconversion of sedoheptulose mono and bisphosphates via D-glycero D-ido octulose-P.

14C labelling of octulose bisphosphates by L-type pentose pathway reactions in liver in situ and in vitro

The complete reaction sequence of the pentose pathway in vitro was studied by incubating [1-14C] ribose 5-phosphate with rat liver enzyme preparation and assessed by both the rate and extent of formation of the glucose 6-P product. The reactions formed, as intermediates, the 1,8-bisphosphates of D-glycero D-ido octulose (D-g D-i Oct) and D-glycero D-altro octulose, both heavily labelled at C-4 with 14C isotope during the 12h incubation. The formation of the octulose phosphates and the specificity of their isotopic labelling confirms an important prediction of, and contribution by reactions of the L-type pentose phosphate pathway (L-PP) in liver in vitro. Infusion in situ of [6-14C] glucose into the liver of the anaesthetized rabbit resulted in the formation of high specific activity [8-14C] D-g D-i Oct 1,8-P2. The specificity of labelling indicates that the octulose intermediate is formed according to the options of the L-PP mechanism of glucose metabolism in intact liver.

Identification and measurement of D-glycero D-ido octulose 1,8-bisphosphate: D-altro-heptulose 7-phosphotransferase enzyme in tissues with L-type pentose phosphate pathway activity

The enzyme D-glycero D-ido octulose 1,8-bisphosphate:D-altro-heptulose 7-phosphotransferase (abbreviated to phosphotransferase, PT) catalyses the transfer of the phosphate ester group at C-1 between altro-heptulose (sedoheptulose) and octulose phosphate intermediates of the L-type pentose pathway. Using synthetically prepared and 14C-labelled octulose mono- and bisphosphates, two methods are described for the measurement of the catalytic capacity of the PT reaction operating in both the "forward" and "reverse" modes of L-type pentose pathway operation. PT activity was found in normal, regenerating and foetal rat liver, rat heart, rat epididymal fat pad, rat kidney, brain and skeletal muscle, extracts of C. fusca, pea leaf and a variety of tumour tissues. The highest activity of the enzyme was found in the neoplasms. The Michaelian kinetic constants, temperature and pH optima for the reaction of the enzyme from rat liver together with an assortment of its substrate specificities have been determined. Vanadate anion was found to inhibit the enzyme and the pattern of inhibition suggests that the PT may act by a sequential mechanism. Neither arabinose 5-phosphate nor inorganic phosphate showed any effect on the catalytic activity of the PT enzyme in liver.

Glucose 6-phosphate formation by L-type pentose phosphate pathway reactions of rat liver in vitro: further evidence

An investigation of the mechanism in vitro of the non-oxidative segment of the pentose phosphate pathway using [5-14C]ribose 5-phosphate as a prediction labelling substrate with rat liver enzyme preparation is reported. Glucose 6-phosphate formed during the initial 0.5 h of reaction was heavily labelled in C-1 and thus is consistent with the prediction of the liver (L)-type pentose phosphate pathway (theoretically C-1/C-6 = 0.5). The reaction sequences of the fat (F-) type pentose phosphate pathway exclusively confine 14C to C-6 of glucose 6-phosphate. The presence of L-type reactions was further affirmed by the formation of D-arabinose 5-phosphate and D-glycero-D-ido-octulose phosphate which were identified and measured during the initial 2 h of incubation using gas liquid chromatography. After 3 h the concentration of 14C in C-1 of glucose 6-phosphate gradually declined and by 17 h of incubation the ratio of 14C in C-1/C-6 was 0.1. Possible reasons for the late changes in 14C-isotope distributions towards a pattern consistent with a contribution of F-type pentose phosphate pathway are given.

Evidence that aldolase and D-arabinose 5-phosphate are components of pentose pathway reactions in liver in vitro

An immunochemical procedure involving the reaction of liver aldolase antibody and rat liver enzyme preparation shows that conversion of ribose 5-P to hexose 6-P by reactions of the non-oxidative pentose pathway fails to occur in the absence of aldolase activity. Radioautography of pentose pathway products formed by liver enzyme catalysis of [U-14C] arabinose 5-P and unlabelled ribose 5-P illustrates the incorporation of 14C into ketopentose, sedoheptulose, fructose and glucose phosphates. There is approximate congruity of the mole specific radioactivity of the pentose and hexose phosphates. These findings are consistent with the proposal that L-pentose pathway reactions constitute the non-oxidative segment of the pathway in liver.

Hyperkalemia due to selective hypoaldosteronism

Hyperkalemia secondary to hyporeninemic hypoaldosteronism with a normal glucocorticoid function was diagnosed in a 47-year-old man with moderate renal insufficiency. Mineralocorticoid administration corrected the hyperkalemia. A probable explanation for hyporeninemia and hypoaldosteronism in this syndrome is that the primary defect is an inability to release renin and the resultant angiotensin deficiency leads to an aldosterone deficiency.

Depression and the reintegration phase of acute schizophrenia

The authors found moderate to severe depression in 60% of a group of schizophrenic patients experiencing acute decompensations (N=30). The course of the depression was followed over an 8-week period8,during which patients were treated with depot fluphenazines. There was a statistically significant reduction in depression that closely paralleled the correction of the cognitive disorder. The authors discuss problems in identifying and quantifying depression during acute schizophrenic decompensation and suggest that the Hamilton scale anxiety/depression factor and the BRPS depression factor may be useful diagnositc tools.

Meningoencephalitis caused by Histoplasma capsulatum: occurrence in a renal transplant recipient and a review of the literature

A case of meningoencephalitis caused by histoplasmosis in a renal transplant patient is described. The diagnosis was made postmortem. The clinicopathological features of 39 additional cases of central nervous system (CNS) invasion by histoplasmosis were reviewed. In the great majority of instances (92.1%), CNS involvement occurred in the disseminated form of the disease. Diagnosis was proved by culturing the fungus from bone marrow, blood, lymph nodes, or liver. Neurological symptoms and signs and cerebrospinal fluid (CSF) changes did not occur until extensive brain damage had resulted. Difficulty in culturing the organism in the (CSF) caused a further delay in making an early diagnosis of CNS involvement. The use of meningeal and brain biopsy specimens in conjunction with the electroencephalogram (EEG) may help in making an earlier diagnosis of CNS involvement.

Calcific cardiomyopathy in advanced renal failure

Four uremic patients on maintenance hemodialysis developed intractable heart failure and atrioventricular block. All had persistently high (over 60) calcium-phosphorus products. At autopsy, all had metastatic myocardial calcification. Their inability to take phosphate-binding agents orally is responsible for this fatal complication.