A homogeneous, high-throughput-compatible, fluorescence intensity-based assay for UDP-N-acetylenolpyruvylglucosamine reductase (MurB) with nanomolar product detection

A novel assay for the NADPH-dependent bacterial enzyme UDP-N-acetylenolpyruvylglucosamine reductase (MurB) is described that has nanomolar sensitivity for product formation and is suitable for high-throughput applications. MurB catalyzes an essential cytoplasmic step in the synthesis of peptidoglycan for the bacterial cell wall, reduction of UDP-N-acetylenolpyruvylglucosamine to UDP-N-acetylmuramic acid (UNAM). Interruption of this biosynthetic pathway leads to cell death, making MurB an attractive target for antibacterial drug discovery. In the new assay, the UNAM product of the MurB reaction is ligated to L-alanine by the next enzyme in the peptidoglycan biosynthesis pathway, MurC, resulting in hydrolysis of adenosine triphosphate (ATP) to adenosine diphosphate (ADP). The ADP is detected with nanomolar sensitivity by converting it to oligomeric RNA with polynucleotide phosphorylase and detecting the oligomeric RNA with a fluorescent dye. The product sensitivity of the new assay is 1000-fold greater than that of the standard assay that follows the absorbance decrease resulting from the conversion of NADPH to NADP(+). This sensitivity allows inhibitor screening to be performed at the low substrate concentrations needed to make the assay sensitive to competitive inhibition of MurB.

Effect of diabetes on enzymes involved in rat hepatic corticosterone production

BACKGROUND

Numerous studies have explored the etiologic or permissive role of 11β-hydroxysteroid dehydrogenase (11β-HSD1) in obesity and Type 2 diabetes, biochemical conditions often with concurrent hyperinsulinism. In contrast, there are limited data on the effect of insulin deficiency (i.e. Type 1 diabetes) on 11β-HSD1 or endoplasmic reticulum enzymes that generate the reduced pyridine cofactor NADPH. Thus, the aim of the present study was to examine the effect of insulin-deficient, streptozotozin diabetes on key microsomal enzymes involved in rat hepatic corticosterone production.

METHODS

After rats had been rendered diabetic with streptozotocin and some had been treated with insulin (2-6 units, s.c., long-acting insulin once daily) for 7 days, hepatic microsomes were isolated. Serum corticosterone and fructosamine were obtained premortem. Intact microsomes were incubated in vitro and 11β-HSD1, hexose-6-phosphate dehydrogenase (H6PDH), and isocitrate dehydrogenase (IDH) measured.

RESULTS

Although diabetes markedly altered body weight gain and serum protein glycosylation (assessed by fructosamine), there was no significant change in hepatic 11β-HSD1 reductase activity, with or without insulin treatment. However, serum corticosterone levels were significantly correlated with 11β-HSD1 reductase activity when all groups were analyzed together (P < 0.05). Untreated diabetes modified (P < 0.01) two hepatic microsomal NADPH-generating enzymes, namely H6PDH and IDH, resulting in a 37% decrease and 14% increase in enzyme levels, respectively.

CONCLUSIONS

Consistent with most in vivo studies, chronic insulin deficiency with attendant hyperglycemia does not significantly modify hepatic 11β-HSD1 reductase activity, but does alter the activity of two microsomal enzymes coupled with pyridine cofactors.

Cooperativity between 11beta-hydroxysteroid dehydrogenase type 1 and hexose-6-phosphate dehydrogenase is based on a common pyridine nucleotide pool in the lumen of the endoplasmic reticulum

11Beta-hydroxysteroid dehydrogenase type 1 (11betaHSD1) is a NADP(H)-dependent oxidoreductase of the ER lumen, which may have an important role in the pathogenesis of metabolic syndrome. Here, the functional coupling of 11beta-hydroxysteroid dehydrogenase type 1 and hexose-6-phosphate dehydrogenase (H6PDH) was investigated in rat liver microsomal vesicles. The results demonstrate the existence of a separate intraluminal pyridine nucleotide pool in the hepatic endoplasmic reticulum and a close cooperation between 11betaHSD1 and H6PDH based on their co-localization and the mutual generation of cofactors for each other.

Properties of neutral cellobiose dehydrogenase from the ascomycete Chaetomium sp. INBI 2-26(–) and comparison with basidiomycetous cellobiose dehydrogenases

The extracellular cellobiose dehydrogenase (CDH) obtained from Chaetomium sp. INBI 2-26(-) has a molecular mass of 95 kDa and an isoelectric point of 5. This novel CDH is highly specific for the oxidation of cellobiose (K(m,app) 4.5 microM) and lactose (K(m,app) 56 microM). With 2,6-dichloroindophenol (DCIP) and cytochrome c(3+) (cyt c(3+)) as electron acceptors, CDH was most active at pH 6. The turnover number of the enzyme for cellobiose, lactose, DCIP and cyt c(3+) was in the range of 9-14s(-1) at 20 degrees C and pH 6. The UV-visible spectrum revealed the flavohemoprotein nature of the enzyme. The cytochrome b domain of the enzyme was reduced by ascorbate, dithionite, as well as specifically by cellobiose in a wide range of pH. The apparent first order rate constants of the spontaneous re-oxidation of the reduced heme domain were estimated as 0.01 and 0.00039 s(-1) at pH 4.5 and 6.5, respectively. The half-inactivation time of CDH at pH 6 and 55 degrees C was ca. 100 min; the stability at pH 8 and, particularly, pH 4 was remarkably lower. Cellobiose stabilized the enzyme against thermal inactivation, whereas DCIP in turn sensitized the enzyme. The new enzyme revealed low affinity for crystalline cellulose, but was capable of binding onto H(3)PO(4)-swollen filter paper. The results show significant differences to already known CDHs and perspectives for several biotechnological applications, where CDH with maximal activity at neutral pH and high affinity for cellobiose and lactose night have some advantages.

Inactivation of GDP-mannose dehydrogenase from Pseudomonas aeruginosa by penicillic acid identifies a critical active site loop

The pathogenic bacterium Pseudomonas aeruginosa synthesizes alginate as one of a group of virulence factors that are produced during infections. The enzyme GDP-mannose dehydrogenase catalyzes the committed step in alginate biosynthesis. We show here that penicillic acid is an irreversible inactivator of GDP-mannose dehydrogenase. Inactivation occurs with a rate constant of 0.39+/-0.01 mM(-1) min(-1) at pH 8.0, and does not exhibit saturation behavior. Partial protection from inactivation is afforded by GDP-mannose, but not by the other substrate, NAD+. GMP and NAD+ together provide complete protection against inactivation. Analysis by mass spectrometry confirmed that the enzyme is alkylated at multiple cysteine residues by penicillic acid, including Cys 213, Cys 246, and the active site cysteine, Cys 268. However, the pH dependence of the inactivation rate suggested that alkylation of a single cysteine residue is sufficient to inactivate the enzyme. The C268A mutant protein was also susceptible to inactivation by penicillic acid. The presence of NAD+ and GMP provided partial protection of Cys 246 and Cys 268, and almost complete protection of Cys 213. Cys 213 is located on a helix that forms part of the binding pocket for GDP-mannose, and forms a hydrogen bond with Asn 252. Asn 252 is located on a loop that surrounds GDP-mannose. The C213A mutant enzyme exhibits a Vmax that is 1.8-fold greater than the wild-type enzyme, suggesting that the interaction between Cys 213 and Asn 252 helps to hold the loop in place during catalysis, and that opening the loop to release product is partially rate-limiting. Cys 246 is adjacent to the GDP-mannose binding loop, and its alkylation may also interfere with loop movement.

Electrochemical investigation of cellobiose dehydrogenase from new fungal sources on Au electrodes

Following previous electrochemical investigations of cellobiose dehydrogenase (CDH), the present investigation reports on the initial screening of the electrochemistry of three new CDHs, two from the white rot basidiomycetes Trametes villosa and Phanerochaete sordida and one from the soft rot ascomycete Myriococcum thermophilum, for their ability to directly exchange electrons with 10 different alkanethiol-modified Au electrodes. Direct electron transfer (DET) between the enzymes and some of the modified Au electrodes was shown, both, in the presence and in the absence of cellobiose. However, the length and the head functionality of the alkanethiols drastically influenced the efficiency of the DET reaction and also influenced the effect of pH on the biocatalytic/redox currents, suggesting the importance of structural/sequence differences between these CDH enzymes. In this respect, the white rot CDHs exhibit excellent biocatalytic and redox currents, whereas for the soft rot CDH the DET communication is much less efficient. Cyclic voltammograms indicate that the heme domain of the CDHs is the part of the enzymes that most readily exchanges electrons with the electrode. However, for P. sordida CDH on 11-mercaptoundecanol or dithiopropionic acid-modified Au electrodes, a second voltammetric wave was noticed suggesting that for some orientations of the enzyme, DET communication with the FAD cofactor can also be obtained.

Interference of laccase in determination of cellobiose dehydrogenase activity ofPleurotus ostreatus (Florida) using dichlorophenol indophenol as the electron acceptor

Pleurotus ostreatus (Florida), ITCC 3308 produces approximately 9.0 U/ml extracellular cellobiose dehydrogenase (CDH) in cellulose medium after 7 days of growth. However, no activity could be detected if the assay was done with cellobiose as the substrate and 2,6-dichlorophenol indophenol (DPIP) as the electron acceptor in absence of any laccase inhibitor. Kinetic study showed that V(max)/K(m) value was very high for rDPIP (reduced 2,6-dichlrophenol indophenol) oxidation by laccase. Oxygen consumption rate of rDPIP oxidation by the enzyme was found to be highest among all the tested substrates. The present study indicated that rDPIP was a good substrate for laccase. Therefore, caution is needed to measure CDH activity by monitoring DPIP reduction in a system where laccase is likely to be present.

[Degradation of the herbicide atrazine by the soil mycelial fungus INBI 2-26(-)--a producer of cellobiose dehydrogenase]

Nonsporulating mycelial fungi producing cellobiose dehydrogenase (CDH) and isolated from soils of South Vietnam with high residual content of dioxins are capable of growing on a solid medium in the presence of high atrazine concentrations (to 500 mg/l). At 20 and 50 mg/l atrazine, the area of fungal colonies was 1.5-1.2-fold larger, respectively, compared with control colonies of the same age, whereas development of the colonies at 500 mg/l atrazine was delayed by 5 days, compared with controls grown in the absence of atrazine. Surface cultivation of the fungus on a minimal medium with glucose as a sole source of carbon and energy decreased the initial concentration of atrazine (20 mg/l) 50 times in 40 days; in addition, no pronounced sorption of atrazine by mycelium was detected. This was paralleled by accumulation in the culture medium of extracellular CDH; atrazine increased the synthesis of this enzyme two- to threefold. Accumulation of beta-glucosidase (a mycelium-associated enzyme) and cellulases preceded the formation of CDH.

Anatomy and fiber type composition of human interarytenoid muscle

Intrinsic laryngeal muscle investigations, especially those of the interarytenoid (IA) muscle, have been primarily teleologically based. We determined IA muscle anatomy and histochemical and immunohistochemical classification of extrafusal and intrafusal (muscle spindle) fibers in 5 patients. Extrafusal fibers were oxidative type I and glycolytic types IIA and IIX. Intrafusal fibers of muscle spindles were identified by the presence of tonic and neonatal myosin. The results demonstrate that the IA muscle has a phenotype similar to that of limb skeletal muscle. Myosin coexpression, the absence of intrafusal fibers, and fiber type grouping were unusual features found previously in the thyroarytenoid and posterior cricoarytenoid muscles, but they were not present in the IA muscle. These findings lead to the conclusion that the IA muscle has functional significance beyond its assumed importance in maintaining vocal fold position during phonation. The presence of spindles demonstrates differences in motor control as compared to the thyroarytenoid and posterior cricoarytenoid muscles. Further, extrafusal fiber characteristics implicate IA muscle involvement in muscle tension dysphonia and adductor spasmodic dysphonia. Given the unique physiologic characteristics of the human IA muscle, further research into the role of the IA muscle in voice disorders is warranted.

Screening of basidiomycete fungi for the quinone-dependent sugar C-2/C-3 oxidoreductase, pyranose dehydrogenase, and properties of the enzyme from Macrolepiota rhacodes

Mycelial cultures of 76 strains of lignocellulose-degrading basidiomycete fungi were screened for the activity of pyranose dehydrogenase, a novel sugar oxidoreductase recently detected in Agaricus bisporus. Of these fungi, 37 strains belonging to seven phylogenetically related genera of mostly litter-decomposing Agaricales were positive for the dehydrogenase, based on activity assays towards D-glucose with 1,4-benzoquinone or ferricenium ion as electron acceptors, and on TLC/HPLC analyses of the reaction products. Lack of activity with O(2) as the oxidant, specificity for C-3 of D-glucose, and active extracellular secretion of the enzyme were used as criteria to differentiate pyranose dehydrogenase from pyranose 2-oxidase (EC 1.1.3.10), known to be produced by numerous wood-rotting fungi. Extracellular pyranose dehydrogenase from Macrolepiota rhacodes was heavily glycosylated. The enzyme was characterized as a 78-kDa flavoprotein under denaturing conditions and a 76-kDa native protein using gel filtration. This enzyme had a maximum extracellular activity of 4.1 U ml(-1) in 39-day liquid cultures. It exhibited broad selectivity for sugar substrates and oxidized D-glucose (K(m)=1.82) exclusively at C-3 to 3-dehydro-D-glucose (D-ribo-hexos-3-ulose), in contrast to pyranose dehydrogenases from Agaricus species, which acted at both C-3 and C-2 of D-glucose. The N-terminal sequence, AVVYRHPDEL, showed significant similarity with that reported for A. bisporus.

Actinic keratosis--a histoenzymological study

Actinic keratosis or senile keratosis is the most frequent premalign epithelial lesion that occurs in the elderly with a history of prolonged and intense exposure to the UV radiation and with an inborn susceptibility. Although the genetics and risk factors are clear nowadays, the histogenesis of this lesion is still under study. The histoenzymologic tests (such as those that demonstrate the ATP-ase and SDH-ase activity) are very useful for early detection of the structural and biochemical changes within the actinic keratosis lesion.

Localization of cellobiose dehydrogenase in cellulose-grown cultures of Phanerochaete chrysosporium

To elucidate the function of cellobiose dehydrogenase (CDH) in cellulose degradation by Phanerochaete chrysosporium, production and localization of CDH were investigated and compared with those in shaking and aerated static cultures grown on cellulose. Substantial CDH activity was detected in the medium of the shake cultures after 8 days of incubation, while no CDH activity was detected in the medium of static cultures at any point during the incubation period. Light microscopy clearly showed that many cellulose particles were adsorbed on the surface of the hypha in static cultures, whereas no cellulose particles were absorbed to the hypha is shake cultures. The addition of laminarinase to static cultures was very effective in detaching cellulose particles from the hypha surfaces. Using a potentiometric assay performed with an oxidation-reduction potential electrode, some CDH activity could be detected on the hypha/cellulose complexes in static cultures. Thus, CDH is produced also in static cultures, albeit in lower amounts that in shake cultures, but the enzyme is not released into the medium. It seem likely that the beta-1,3-glucan layer plays an important role in CDH localization and cellulose degradation. Immunocytochemical confocal laser scanning microscopy for the static cultures demonstrated that most CDH was adsorbed on the surface of the cellulose, especially around the cracks, which were formed by the action of cellulases during the course of incubation. From these observations, we conclude a direct participation of CDH in the degradation of cellulose in cooperation with cellulases.

Tissue-specific accumulation of MURB, a protein encoded by MuDR, the autonomous regulator of the Mutator transposable element family

The Mutator (Mu) system of transposable elements is highly mutagenic and can maintain high levels of activity through multiple generations due to frequent transpositions of both its autonomous and nonautonomous components. This family also shows pronounced developmental regulation. Most notable is the very low frequency of germinal reversions, despite the high levels of somatic transpositions and excisions, and the high frequency of germinally transmitted duplication events. Here, we report the production of antibodies raised against MURB, one of two proteins encoded by MuDR, the autonomous regulator of the Mu family. Immunolocalizations performed using anti-MURB antibodies reveal that this protein is present in specific tissues during male inflorescence development. Throughout much of development, MURB is detected at the highest levels in cell lineages that may find themselves in the germ line, but no MURB is detected in microspore mother cells. These cells are the direct precursors to pollen. Based on these observations as well as previous data, we discuss the relationship between the expression of MURB and developmental regulation of Mu activity.

Biochemical characterization of gapB-encoded erythrose 4-phosphate dehydrogenase of Escherichia coli K-12 and its possible role in pyridoxal 5'-phosphate biosynthesis

One step in de novo pyridoxine (vitamin B6) and pyridoxal 5'-phosphate biosynthesis was predicted to be an oxidation catalyzed by an unidentified D-erythrose-4-phosphate dehydrogenase (E4PDH). To help identify this E4PDH, we purified the Escherichia coli K-12 gapA- and gapB-encoded dehydrogenases to homogeneity and tested whether either uses D-erythrose-4-phosphate (E4P) as a substrate. gapA (gap1) encodes the major D-glyceraldehyde-3-phosphate dehydrogenase (GA3PDH). The function of gapB (gap2) is unknown, although it was suggested that gapB encodes a second form of GA3PDH or is a cryptic gene. We found that the gapB-encoded enzyme is indeed an E4PDH and not a second GA3PDH, whereas gapA-encoded GA3PDH used E4P poorly, if at all, as a substrate under the in vitro reaction conditions used in this study. The amino terminus of purified E4PDH matched the sequence predicted from the gapB DNA sequence. Purified E4PDH was a heat-stable tetramer with a native molecular mass of 132 kDa. E4PDH had an apparent Km value for E4P [Kmapp(E4P)] of 0.96 mM, an apparent kcat catalytic constant for E4P [kcatapp(E4P)] of 200 s-1, Kmapp(NAD+) of 0.074 mM, and kcatapp(NAD+) of 169 s-1 in steady-state reactions in which NADH formation was determined. From specific activities in crude extracts, we estimated that there are at least 940 E4PDH tetramer molecules per bacterium growing in minimal salts medium plus glucose at 37 degrees C. Thin-layer chromatography confirmed that the product of the E4PDH reaction was likely the aldonic acid 4-phosphoerythronate. To establish a possible role of E4PDH in pyridoxal 5'-phosphate biosynthesis, we showed that 4-phosphoerythronate is a likely substrate for the 2-hydroxy-acid dehydrogenase encoded by the pdxB gene. Implications of these findings in the evolution of GA3PDHs are also discussed. On the basis of these results, we propose renaming gapB as epd (for D-erythrose-4-phosphate dehydrogenase).

An indirect free radical-based assay for the enzyme cellobiose:quinone oxidoreductase

A sensitive and quantitative assay for the detection of cellobiose:quinone oxidoreductase (CBQase) is described. The assay is based on the ability of CBQase to reduce the cation radicals formed by the laccase-mediated oxidation of chlorpromazine (CPZ). Formation of the CPZ radical cation is readily followed at 530 nm, and the net rate of its formation is decreased in proportion to the amount of CBQase activity present. Advantages of this assay are its increased sensitivity due to the high extinction coefficient of the CPZ radical, the high solubility of the substrate in water, and the assay's ability to detect reductive activity in the presence of laccase and other oxidative enzymes. The assay also detects other enzymes, such as glucose oxidase, which have CPZ radical-reducing activity.

FAD-glycerophosphate dehydrogenase activity in pancreatic islets and liver of ob/ob mice

The activity of FAD-glycerophosphate dehydrogenase, as measured through the generation of either 3HOH from L-[2-3H]glycerol-3-phosphate in the presence of FAD or iodoformazan from iodonitrotetrazolium, displayed comparable values in islet homogenates of lean and obese (ob/ob) mice. In the liver of the obese animals, the results obtained by the colorimetric and radioisotopic assays yielded a paired ratio twice higher than in control mice. Although isoforms of the mitochondrial enzyme could be present in variable proportions depending on the cell type and genetic background, the present results suggest that, in ob/ob mice, the increased secretory responsiveness of the islet B-cell to D-glucose coincides with an unaltered activity of FAD-glycerophosphate dehydrogenase. This contrasts with the situation recently documented in db/db mice, in which an impaired secretory response of the B-cell to D-glucose is associated with a decreased activity of FAD-glycerophosphate dehydrogenase.

Enzymatic, metabolic and secretory perturbations in pancreatic islets of thyroidectomized rats

In thyroidectomized rats, the activity of FAD-linked glycerophosphate dehydrogenase was severely diminished in liver homogenates but not affected significantly in pancreatic islet homogenates, whilst the activity of 2-ketoglutarate dehydrogenase was decreased modestly in both liver and islet homogenates. Likewise, in intact islets of thyroidectomized rats, the generation of 3HOH from [2-3H]glycerol was not decreased, and the ratio between oxidative and total glycolysis not significantly lower than in islets from sham-operated rats, at least in the presence of a high concentration of D-glucose. Nevertheless impaired oxidation of both D-[3,4-14C]glucose and D-[6-14C]glucose was observed in islets of thyroidectomized rats, the relative magnitude of such a decrease being more pronounced at a low than at a high D-glucose concentration. Such metabolic anomalies coincided with a lower level of plasma insulin and decreased output of insulin by islets incubated at low (2.8 mM), but not higher, concentrations of D-glucose. It is concluded that hypothyroidism does not mimic the deficiency in islet FAD-linked glycerophosphate dehydrogenase activity found in rats with inherited or acquired non-insulin-dependent diabetes.

Effects of growth temperature on alginate synthesis and enzymes in Pseudomonas aeruginosa variants

Spontaneous variation of the level of alginate synthesis in Pseudomonas aeruginosa was associated with changes in the activity of all four enzymes leading to synthesis of GDP-mannuronic acid, the activated precursor for polymerization. For the high-alginate-producing variant 8821M, alginate yield and properties, as well as the levels of alginate enzymes, were dependent on growth temperature. In contrast, levels of alginate and enzymes in the mucoid parent strain 8821 were very low and near temperature-independent. The difference in the specific activity of GDP-mannose dehydrogenase (GMD), encoded by the algD gene, between the two strains was associated with the alginate biosynthetic ability and with the degree of activation of the algD promoter, measured using the algD-xylE transcription fusion on plasmid pVD2X. Maximal activity of the four enzymes was observed in strain 8821M grown at 30 degrees C, a temperature below the optimum for growth (35 degrees C). The effect of temperature on GMD activity could not be explained by the regulation of the algD promoter by temperature, since expression of pVDZX appeared to be more active at 35 degrees C, when the decrease of pVD2X copy number with increasing temperature was taken into account. The involvement of enzymes that catalyse steps downstream from the formation of the activated precursor should also be considered, as suggested by differences in the molecular mass of alginates synthesized by the two strains at various temperatures. Acetyl content of alginates increased as temperature decreased and strain 8821M produced the highest levels of acetylated polymers. The degree of acetylation appeared to be related to growth rate and could reflect acetyl-CoA availability.

Enzymatic properties of isozymes and variants of glucose dehydrogenase from Bacillus megaterium

Three glucose dehydrogenases (GlcDH) from Bacillus megaterium, GlcDH-I, GlcDH-II and GlcDH-IWG3, were purified from Escherichia coli cells harboring one of the hybrid plasmids, pGDK1, pGDK2 and pGDA3, respectively, pGDK1 and pGDK2 contain two isozyme genes, gdhI and gdhII, respectively, from B. megaterium IAM 1030 and pGDA3 contains an isozyme gene from B. megaterium IWG3; GlcDH-IWG3 is a variant of GlcDH-I. GlcDH-I and GlcDH-II have similar pH/activity profiles and the profile for GlcDH-IWG3 is identical to that of GlcDH-I. The pH/stability profiles of these enzymes show that GlcDH-IWG3 is the most stable enzyme in the acidic region, while GlcDH-II is the most stable in the alkaline region, and GlcDH-I is the most unstable throughout the entire pH range examined. As for thermostability, GlcDH-II is the most resistant against heat inactivation at pH 6.5. The values of the first-order rate constant for heat inactivation at 50 degrees C are 0.27 min-1, 0.05 min-1 and 0.11 min-1 for GlcDH-I, GlcDH-II and GlcDH-IWG3, respectively. Kinetic studies show that these enzymes have similar kinetic constant values except that there are some differences in Kia for NAD(P) and Ka (the limiting Michaelis constant) for NAD; the values of the ratio of Kia for NAD and NADP are 11,340 and 8.7 for GlcDH-I, GlcDH-II and GlcDH-IWG3, respectively. GlcDH-I and GlcDH-IWG3 have very similar substrate specificities and GlcDH-II has a slightly higher specificity for D-glucose and 2-deoxy-D-glucose than the others. The results are discussed on the basis of the amino acid substitutions between the enzymes.

Biosynthesis of glycosaminoglycan precursors: evidences for different tissue specific forms of UDP-glucose dehydrogenase

UDP-glucose dehydrogenase (UDPGDH) was extracted and partially purified from different rat tissues and the kinetic parameters and some properties of the enzyme were determined and compared. The pH optimum ranged between 8.6 and 9.4 for liver and kidney UDPGDH and between 8.4 and 8.6 for skin and lung UDPGDH. Liver and kidney enzymes showed a similar affinity for both UDPG and NAD. Lung and skin enzymes also showed similar affinity for both substrates, which differed however from that of liver and kidney UDPGDH. Both liver and kidney enzymes had a higher heat stability and a different electrophoretic mobility compared to skin and lung UDPGDH. These data suggest the existence of different tissue specific forms of the enzyme.

Uridine diphosphoglucose dehydrogenase activity in normal and osteoarthritic human chondrocytes

The activity of uridine diphosphoglucose dehydrogenase (UDPGD), a key enzyme in the synthesis of proteoglycans was measured by a quantitative cytochemical method in normal and in osteoarthritic (OA) human cartilage. Normal adult chondrocytes showed low UDPGD activity, which was about half the activity of glucose-6-phosphate dehydrogenase of the same specimens. No significant increase in UDPGD activity was noted in OA chondrocytes. The lack of significantly enhanced UDPGD activity in OA indirectly agrees with studies showing normal 35S uptake in this disease and might explain in part the inability of chondrocytes to cope with continuous proteoglycan loss.

The nucleotide sequence of the serA gene of Escherichia coli and the amino acid sequence of the encoded protein, D-3-phosphoglycerate dehydrogenase

The nucleotide sequence of serA, the structural gene of Escherichia coli which codes for D-3-phosphoglycerate dehydrogenase, has been determined. The structural gene contains 1233 nucleotides which code for the 409 amino acids of the subunit of the tetrameric enzyme, as well as the initiator methionine, which is cleaved from the mature protein, and the termination codon. The majority of the primary structure of the enzyme has been confirmed by automated Edman degradation of peptide fragments produced by a variety of cleavage agents. Comparison of the amino acid sequence of phosphoglycerate dehydrogenase with other NAD-dependent oxidoreductases reveals less than 20% homology, although conservation of certain specific residues in the coenzyme binding domain appears to be evident.

A cellulase assay coupled to cellobiose dehydrogenase

An assay for cellulase activity based on the oxidation of cellobiose, formed during the cellulase reaction, with ferricyanide and a cellobiose dehydrogenase derived from the cellulolytic fungus Sporotrichum (Chrysosporium) thermophile is presented. Due to the restricted specificity of this enzyme for cellobiose and cellodextrins, glucose, which may be formed by the action of some cellulolytic components or by beta-glucosidase, does not contribute to the result. The negative interference of beta-glucosidase may be eliminated by glucono-delta-lactone inhibition. The assay, which is not influenced by cellobiose back-inhibition of the cellulase reaction, like the usual cellulase tests based on the increase in reducing power, is basically unspecific with respect to endo- or exo-acting enzymes giving rise to a total cellulase activity. With the use of an amorphous cellulose substrate (reprecipitated cellulose after dissolving in concentrated phosphoric acid), unpredictable effects due to cooperativity between endo- and exo-enzyme components were eliminated. An analytical procedure giving a linear response between activity and enzyme concentration and between activity and time of incubation has been worked out.

Evidence for the homology of hexose 6-phosphate dehydrogenase and glucose 6-phosphate dehydrogenase: comparison of the amino acid compositions

Amino acid compositions of hexose 6-phosphate dehydrogenase and glucose 6-phosphate dehydrogenase from crucian carp and rat, and that of sea-urchin glucose 6-phosphate dehydrogenase were compared in order to ascertain if they are homologous enzymes. The results demonstrated that the overall amino acid compositions of the two enzymes remarkably resemble each other, and that the composition divergence (D = 0.038) of the crucian carp enzymes is in the range of those for homologous proteins so far reported. These findings strongly support our previous prediction that the two enzymes have diverged from a common ancestral molecule.

Mouse liver microsomal hexose-6-phosphate dehydrogenase. NADPH generation and utilization in monooxygenation reactions

Hexose-6-phosphate dehydrogenase (H6PD) activity in washed hepatic microsomes from male ICR mice, when assayed with NADP+ and deoxyglucose-6-phosphate, was partially latent. Brief sonication or detergents activated H6PD causing an approximately 4- and 8.5-fold increase in NADPH generation respectively. The sonicated microsomes exhibited H6PD-linked N-demethylase activity toward aminopyrine. This activity was best sustained in the presence of deoxyglucose-6-phosphate, while galactose-6-phosphate, glucose-6-phosphate, and glucose were less effective. Reaction media containing sonicated microsomes, NADP+ and deoxyglucose-6-phosphate also catalyzed N-demethylation of p-chloro-N-methylaniline, N,N-dimethylaniline and nicotine, O-demethylation of p-nitroanisole, p-hydroxylation of aniline, ring hydroxylation of biphenyl at the 2- and 4-positions, dearylation of parathion, and the N-oxidation of N,N-dimethylaniline. In general, the hexose-6-phosphate dehydrogenase-linked monooxygenation rates were 60% or more of those observed in the presence of exogenous NADPH.

Intramembraneous localization of rat liver microsomal hexose-6-phosphate dehydrogenase and membrane permeability to its substrates

A method for purifying hexose-6-phosphate dehydrogenase (beta-D-glucose: NAD(P) -oxidoreductase, EC 1.1.1.47) from rat liver microsomes is described. The purified enzyme was shown to be homogeneous by sodium dodecyl sulfate (SDS)-polyacrylamide electrophoresis. It is shown that the enzyme is bound to the inner surface of microsomal membranes, and that glucose 6-phosphate, but not NADP, penetrates almost freely into the membranes at 37 degrees C.

Growth dependence of phosphoglyceric acid dehydrogenase activity in cultured rat liver cells

Rat liver epithelial cells in culture (WIRL-3C) have the enzymes that synthesize serine from 3-phophoglyceric acid. Both phosphoglyceric acid dehydrogenase (PGAD) and serine-phosphate (serine-P) forming activities fluctuate with time after subculture and are higher in growing than confluent cells. This activity pattern was not common for other dehydrogenases in WIRL-3C cells, nor was it common for PGAD activity in other cultured cells. At time of subculture, cells are removed from spent medium, treated with trypsin, and fed fresh medium. None of these parameters causes the rise in activity; in contrast, reduction in cell density and the accompanying stimulation of growth do. PGAD activity decreases when growth is slowed either as the cells progress to the end of the culture cycle, when cells are treated with dexamethasone-phosphate (Dx-P) or dibutyryl cyclic AMP(cAMP) and theophylline or when the serum concentration of the medium is reduced to 0.2%. Under these conditions, decreased PGAD activity is paralleled by a decline in growth and DNA accumulation. PGAD activity in WIRL-3C cells is regulated in a manner closely resembling what has been observed previously in rat liver from the whole animal. The possible use of this system in studying regulation of gene expression in mammalian cells is discussed.

Isolation and characterization of outer and inner membranes from Pseudomonas aeruginosa and effect of EDTA on the membranes

The outer and inner cytoplasmic membranes of Pseudomonas aeruginosa were separated as small and large membranes, respectively, from the cell envelope of this organism treated with lysozyme in Tris-chloride buffer containing sucrose and MgCl2 by differential centrifugation. The small membrane fraction contained predominantly 2-keto-3-deoxyoctonate (KDO), and little cytochromes or oxidase activities. The small membrane was composed of only 9 polypeptides and showed homogeneous small vesicles electron-microscopically. On the other hand, the large membrane fraction had high cytochrome contents and oxidase activities, and little KDO. The large membrane was composed of a number of polypeptides and showed large fragments or vesicles electron-microscopically. These results indicate that the small and large membranes are the outer and inner cytoplasmic membranes of P. aeruginosa, respectively. The isolated outer membrane showed a symmetrical protein peak with a density of 1.23 on sucrose density gradient centrifugation and the isolated inner membrane showed an unusually high density, probably due to association with ribosomes and extrinsic or loosely bound proteins. EDTA lowered the density of both membranes and caused lethal damage to the outer membrane, causing disintegration with the release of lipopolysaccharide (LPS), proteins and phospholipid.

Localization of human gene loci using spontaneous chromosome rearrangements in human-Chinese hamster somatic cell hybrids

Analysis of human-Chinese hamster somatic cell hybrids with spontaneously derived chromosome structural changes has provided data for the regional and subregional localization of gene loci which have previously been assigned to human chromosomes 2, 12, and X. Correlation of the expression of human gene loci with the human chromosome complements present in somatic cell hybrids indicates that the cytoplasmic malate dehydrogenase (MDH1) locus is in the 2p23yields2pter region, and red cell acid phosphatase (AcP1) is at or adjacent to 2p23. The cytoplasmic isocitrate dehydrogenase (IDH1) locus is at or adjacent to 2q11, peptidase B (Pep B) is at or adjacent to 12q21, lactate dehydrogenase B (LDH B) is in the 12q21yiedls12pter region, glucose-6-phosphate dehydrogenase (G6PD) is in the Xq24yieldsXqter region, and the gene loci for phosphoglycerate kinase (PGK), alpha-galactosidase (alpha-gal), and hypoxanthine guanine phosphoribosyltransferase (GPRT) are in the Xp21yieldsXq24 region.