Lactate dehydrogenase isozymes from mouse

Effects of caloric restriction and ketogenic diet on renal fibrosis after ischemia/reperfusion injury

The beneficial effects of caloric restriction (CR) and a ketogenic diet (KD) have been previously shown when performed prior to kidney injury. We investigated the effects of CR and KD on fibrosis development after unilateral kidney ischemia/reperfusion (UIR). Post-treatment with CR significantly (p < 0.05) affected blood glucose (2-fold decrease), ketone bodies (3-fold increase), lactate (1.5-fold decrease), and lipids (1.4-fold decrease). In the kidney, CR improved succinate dehydrogenase and malate dehydrogenase activity by 2-fold each, but worsened fibrosis progression. Similar results were shown for the KD, which restored the post-UIR impaired activities of succinate dehydrogenase, malate dehydrogenase, and α-ketoglutarate dehydrogenase (which was decreased 2-fold) but had no effect on fibrosis progression. Thus, our study shows that the use of CR or KD after UIR did not reduce the development of fibrosis, as shown by hydroxyproline content, western-blotting, and RT-PCR, whereas it caused significant metabolic changes in kidney tissue after UIR.

Fibrosis Development Linked to Alterations in Glucose and Energy Metabolism and Prooxidant-Antioxidant Balance in Experimental Models of Liver Injury

The development of liver fibrosis is one of the most severe and life-threatening outcomes of chronic liver disease (CLD). For targeted therapy of CLD, it is highly needed to reveal molecular targets for normalizing metabolic processes impaired in damaged liver and associated with fibrosis. In this study, we investigated the morphological and biochemical changes in rat liver models of fibrosis induced by chronic administration of thioacetamide, carbon tetrachloride, bile duct ligation (BDL), and ischemia/reperfusion (I/R), with a specific focus on carbohydrate and energy metabolism. Changes in the levels of substrates and products, as well as enzyme activities of the major glucose metabolic pathways (glycolysis, glucuronidation, and pentose phosphate pathway) were examined in rat liver tissue after injury. We examined key markers of oxidative energy metabolism, such as the activity of the Krebs cycle enzymes, and assessed mitochondrial respiratory activity. In addition, pro- and anti-oxidative status was assessed in fibrotic liver tissue. We found that 6 weeks of exposure to thioacetamide, carbon tetrachloride, BDL or I/R resulted in a decrease in the activity of glycolytic enzymes, retardation of mitochondrial respiration, elevation of glucuronidation, and activation of pentose phosphate pathways, accompanied by a decrease in antioxidant activity and the onset of oxidative stress in rat liver. Resemblance and differences in the changes in the fibrosis models used are described, including energy metabolism alterations and antioxidant status in the used fibrosis models. The least pronounced changes in glucose metabolism and mitochondrial functions in the I/R and thioacetamide models were associated with the least advanced fibrosis. Ultimately, liver fibrosis significantly altered the metabolic profile in liver tissue and the flux of glucose metabolic pathways, which could be the basis for targeted therapy of liver fibrosis in CLD caused by toxic, cholestatic, or I/R liver injury.

Identification of human LDHC4 as a potential target for anticancer drug discovery

One of the distinct hallmarks of cancer cells is aerobic glycolysis (Warburg effect). Lactate dehydrogenase A (LDHA) is thought to play a key role in aerobic glycolysis and has been extensively studied, while lactate dehydrogenase C (LDHC), an isoform of LDHA, has received much less attention. Here we showed that human LDHC was significantly expressed in lung cancer tissues, overexpression of Ldhc in mice could promote tumor growth, and knock-down of LDHC could inhibit the proliferation of lung cancer A549 cells. We solved the first crystal structure of human LDHC4 and found that the active-site loop of LDHC4 adopted a distinct conformation compared to LDHA4 and lactate dehydrogenase B4 (LDHB4). Moreover, we found that (ethylamino) (oxo)acetic acid shows about 10 times selective inhibition against LDHC4 over LDHA4 and LDHB4. Our studies suggest that LDHC4 is a potential target for anticancer drug discovery and (ethylamino) (oxo)acetic acid provides a good start to develop lead compounds for selective drugs targeting LDHC4.

Organophosphorus insecticide, monocrotophos, possesses the propensity to induce insulin resistance in rats on chronic exposure

BACKGROUND

Our earlier studies had shown that monocrotophos (MCP), an organophosphorus insecticide (OPI), has the propensity to augment the secondary complications associated with type-1 diabetes. The present study investigates whether rats exposed for prolonged periods to monocrotophos would develop insulin resistance mediated by alteration in glucose homeostasis.

METHODS

Male rats were administered sublethal doses of monocrotophos daily for 180 days. Interim blood samples were collected to measure alteration in blood glucose and lipid profile. Rats were also subjected to glucose and insulin tolerance test and fasting blood glucose and insulin levels were measured to calculate insulin resistance by HOMA-IR method. After 180 days, the rats were also evaluated for pancreatic histology and activities of hepatic gluconeogenetic enzymes.

RESULTS

Monocrotophos elicited a gradual and sustained increase in blood glucose and insulin resistance in rats with concomitant glucose intolerance and reduced insulin sensitivity. MCP exposure was also associated with increase in weights of key white adipose pads, activities of gluconeogenesis enzymes and increase in pancreatic islet diameter, all of which led to hyperglycemia, hyperinsulinemia and dyslipidaemia.

CONCLUSION

Long-term exposure of rats to MCP resulted in glucose intolerance with hyperinsulinemia, a hallmark of insulin resistance. Our data suggest that chronic exposure to low doses of monocrotophos, might lead to development of insulin resistance by altering lipid profile and glucose homeostasis.

Inhibitor screening of lactate dehydrogenase C4 from black-lipped pika in the Western Sichuan Plateau

Studies indicated that lactate dehydrogenase C4 (LDH-C4) was a good target protein for development of contraceptive drugs. Virtual screening and in vitro enzyme assay using pika LDH-C4 as target protein revealed NSC61610, NSC215718, and NSC345647 with Ki of 7.8, 27, and 41 μM separately. This study might be helpful for development of pika contraceptive drugs.

Severe, short-term food restriction improves cardiac function following ischemia/reperfusion in perfused rat hearts

The purpose of this study was to clarify the characteristics of improved ischemic tolerance induced by severe, short-term food restriction in isolated, perfused rat hearts. Male Wistar (8 week-old) rats were given a food intake equivalent to a 70% reduction on the food intake of ad-libitum fed rats for 11 days (FR group and AL group, respectively). After this period, hearts were isolated and perfused in the Langendorff mode, and subjected to 20 min of global ischemia followed by 30 min of reperfusion. Although the coronary flow rate in the FR group (63.0 +/- 3.1 ml/min/g dry weight) was higher than that in the AL group (47.1 +/- 1.3 ml/min/g dry weight) during preischemic perfusion, the lactate release into the coronary effluent and absolute values of +dP/dt and -dP/dt in the FR group (2422 +/- 161 and -1282 +/- 51) were inversely lower than in the AL group (2971 +/- 156 and -1538 +/- 74, respectively). An increase in ischemic contracture was suppressed in the FR group. Following reperfusion, cardiac function, high-energy phosphate content, and intracellular pH, as measured by 31P-nuclear magnetic resonance spectroscopy, had recovered to a much greater degree in the FR group than in the AL group. The serum T3 level was significantly lower in the FR group (2.7 +/- 0.1 pg/ml) than in the AL group (3.6 +/- 0.1 pg/ml), and the levels of triglycerides, free fatty acids, insulin, and glucose were also significantly lower in the FR group than in the AL group. The protein expressions of myocyte enhancer factor 2A, Na(+), K(+)-ATPase, and phospholamban in the cardiac tissue were higher in the FR group than in the AL group. These results suggested that severe, short-term food restriction improves ischemic tolerance in rat hearts via altered expression of functional proteins induced by low serum T3 levels, decreased coronary conductance, and change in metabolic flux.

Induction of the intrinsic apoptotic pathway in cells infected with cytopathic bovine virus diarrhoea virus

Cytopathic bovine viral diarrhoea virus (cp BVDV) induces apoptosis in bovine cell cultures. This also seems to be a prominent feature in the pathogenesis of mucosal disease. To gain an insight into the molecular pathways of the cell alterations, the involvement of different members of the apoptotic cascade was analyzed. It was shown that inhibition of the mitochondrial permeability transition pore significantly delayed the cytopathic effect without affecting virus replication. Moreover, the membrane potential (deltapsi(m)) was affected, and translocation of cytochrome c to the cytosol, overexpression of apoptotic protease-activating factor 1 and a significant increase of caspase-9 activity were demonstrated, indicating that the apoptosome is formed. We conclude that at least in vitro, infection of cells with cp BVDV leads to the activation of the intrinsic pathway of apoptosis.

Localization of viral proteins in cells infected with bovine viral diarrhoea virus

Bovine viral diarrhoea virus (BVDV) is a member of the genus Pestivirus within the family Flaviviridae. In this report, protein localization studies were performed to assess the mechanism for the release of mature virus particles from infected cells. Since BVDV is an enveloped virus, budding from either intra- or extracellular membranes is feasible. A prerequisite for the latter mechanism is the integration of viral glycoproteins into the host cell membrane. Using monoclonal antibodies (MAbs) directed against the viral envelope glycoproteins E2 and E(RNS), no specific signals were detected on the surface of BVDV-infected cells by indirect fluorescence, confocal microscopy or fluorescence-activated cell sorter analyses. Furthermore, biotin-labelled cell surface proteins of virus-infected and non-infected cells were not detected by immunoprecipitation using MAbs directed against E(RNS) and E2 or the non-structural protein NS2-3. None of these proteins was detected on the cell surface. In addition, to analyse the intracellular localization of the two viral glycoproteins E(RNS) and E2 and the non-structural proteins NS2-3 and NS3, subcellular fractionation of virus-infected cells followed by radioimmunoprecipitation with the MAbs were performed. These results led to the conclusion that the BVDV envelope glycoproteins E(RNS) and E2 as well as the non-structural proteins NS2-3 and NS3 were almost quantitatively associated with intracellular membranes. These findings indicate that BVDV is released by budding into the cisternae of the endoplasmic reticulum and that there seems to be no correlation between the location and function of the analysed proteins.

Molecular and kinetic properties of sperm specific LDH after radiation inactivation

Radiation inactivation of sperm specific lactate dehydrogenase-C4 (LDH-C4) has been studied and compared with the somatic LDH in aqueous solution. D37 of C isozyme was 470 Gy and that of B isozyme was 520 Gy. Semi-log plots of log N/No versus dose suggested that the inactivation of two LDH isozymes in presence of normal saline follows a single hit kinetics. Target molecular weight calculated by radiation analysis was found as 1.52 x 10(5) gm/mole for LDH-C4 and 1.38 x 10(5) gm/mole for LDH-B4. SDS-PAGE of irradiated enzymes showed a band of 35 kDa but did not indicate the presence of any other extra band, when compared with sham-irradiated enzymes. Chemical kinetics of residual activity following irradiation at D37 showed decrease in Vmax with coenzymes and primary substrates. However, decrease in Km was seen with pyruvate as increasing substrate. Nevertheless, K did not change when NAD+ was the leading substrate for LDH-B4 or LDH-C4. A hyperchromicity in intrinsic fluorescence and a blue shift in lambdamax over sham-irradiated LDH-C4 revealed the exposure of buried tryptophan residues to the surface after radiation inactivation. Results suggest that inspite of presence of variant amino acids, the conformations of two isozymes are stabilized by similar forces which behave in a similar way for radiation inactivation in aqueous phase.

Evaluation of the mutagenicity of acetochlor to male rat germ cells

Male rat dominant lethal (DL) assays conducted on the herbicide acetochlor are described. Single dose studies conducted at the maximum tolerated dose (MTD, < or = 1000 mg/kg) produced no effects on any of the DL assay parameters at any of the ten weekly sampling periods. It is concluded that acetochlor is non-mutagenic to rat germ cells. Due to initial limited knowledge of the MTD of acetochlor it was also evaluated in the DL assay at a dose level of 2000 mg/kg. At this high dose level severe bodyweight loss and some deaths occurred among the treated animals. In addition, reduced implantations and reduced pregnancy rates were observed at the third sampling period (18-25 days post dosing) in the absence of an increase in early post-implantation deaths. These results indicated that the use of supra-MTD doses of acetochlor had reduced the fertility of the treated males leading to the production of a pseudo-DL assay response, as alerted to and defined by Ehling. Although several such pseudo-DL assay responses have been described, none have been explained mechanistically. It was therefore decided to pursue the effects seen in the DL assay when using supra-MTD doses of acetochlor. Ova analysis of female rats mated with male rats exposed to 2000 mg/kg acetochlor revealed unfertilized ova at the critical third sampling time. Normal fertilization of ova was observed at the first and fifth sampling period and, for a dose of 200 mg/kg acetochlor, at the third sampling period. The magnitude and temporal nature of these effects confirmed the induction of a pseudo-DL assay response, and studies were then undertaken to probe its genesis. Rats treated with 2000 mg/kg acetochlor had normal testicular and epididymal pathology and normal sperm numbers and sperm motility at the critical third sampling period. Despite a small reduction in testicular and epididymal glutathione levels 12 h after exposure to 2000 mg/kg acetochlor, testicular LDH and LDH-X enzyme levels were unaffected. Further, no reduction in the level of free sulphydryl groups (-SH) were observed in epididymal caput sperm heads isolated 0.5, 7 or 14 days after treatment of male rats with 2000 mg/kg acetochlor. The only sperm parameter affected by treatment with 2000 mg/kg acetochlor was an increase in epididymal cauda sperm with head abnormalities. The non-specific nature of this effect was considered inadequate to explain fully the high dose fertility effects seen in the DL assays, which therefore remain unexplained. The present data establish that acetochlor is non-mutagenic to rat germ cells. They also confirm the importance of segregating mutagenic and fertility effects in the DL assay, and emphasize the need for appropriate dose-setting studies prior to the conduct of rodent genetic toxicity assays.

Rapid and large-scale isolation of microsomal fraction of mouse liver by lyophilization and low speed centrifugation

We could prepare the microsomal fraction of mouse liver, without using an ultracentrifuge but with a low speed centrifuge. The procedure includes 1) lyophilization of post-mitochondrial fraction (9,000 x g supernatant) of mouse liver, 2) powdering of the lyophilized sample, 3) the addition of 1.15 per cent potassium chloride solution or distilled water, which afforded microsomal aggregates, 4) sedimentation of microsomal fraction by low-speed centrifugation (20,000 x g, 20 min). The sedimented microsomal fraction showed normal contents of cytochrome P-450 and cytochrome b5, and gave a normal pattern on SDS polyacrylamide gel electrophoresis and normal electron microscopic feature. This method should be convenient for rapid and large-scale preparation of microsomes, especially for the preparation of cytochrome b5 and cytochrome P-450.

Biochemical markers of early and late spermatogenesis: relationship between the lactate dehydrogenase-X and creatine kinase-M isoform concentrations in human spermatozoa

As part of our research program on biochemical markers of sperm maturity, we have studied sperm creatine kinase (CK) and lactate dehydrogenase (LDH) concentrations and the isoform ratios of the CK-M [% CK-M/(CK-M + CK-B)] and LDH-X [% LDH-X/(LDH-X + LDH-a)] in 50 oligospermic and 95 normospermic men [corrected]. Because the synthesis of LDH-X is initiated in early spermatogenesis, and that of CK-M commences in late spermiogenesis simultaneously with cytoplasmic extrusion, we proposed two working hypotheses:(1) LDH and CK concentrations reflect the retained cytoplasm in sperm, thus the activities of both enzymes will be related and will be higher in oligospermic specimens, which have a higher incidence of immature spermatozoa; and (2) because in normally developed sperm both LDH-X and CK-M are present, there will be a correlation between LDH-X and CK-M ratios in the mature sperm populations. However, among men with immature sperm samples with late spermiogenetic defect and diminished CK-M ratios, there will be two groups: one which completed spermatogenesis prior to spermiogenetic failure (normal LDH-X and diminished CK-M ratios), and another group with defects in both spermatogenesis and spermiogenesis (low LDH-X and diminished CK-M ratios). Because of this heterogeneity, LDH-X ratios will be a poor predictor of sperm maturity. The data support the hypotheses: (1) LDH and CK concentrations were higher in oligospermic vs. normospermic men (P < 0.001). (2) The LDH and CK concentrations were related (r = 0.65, P < 0.001, N = 145), and there were inverse correlations between CK, LDH, LDH-X, or CK-M ratios vs. sperm concentrations (P < 0.001 in all four). (3) The CK-M and LDH-X ratios were different between the oligospermic and normospermic groups (P < 0.001), although the means of the LDH-X ratios were narrower (LDH-X:1:1.3; CK-M:1:1.9). (4) Dividing the 145 samples by the cut-off value of mean minus 1 SD of the CK-M and LDH-X ratios (11% and 32%, respectively) demonstrated that the CK-M ratios discriminated better than LDH-X ratios between the samples with mature and immature sperm. These data on the biochemical markers of early and late spermatogenesis support the studies in which CK better reflected sperm quality than LDH or LDH-X (Orlando et al., 1994: Int J Androl 17:13-18) and the > 10% sperm CK-M ratio predicted with a rate of 30.4% per cycle in the occurrence of pregnancies in a blinded study of 84 IVF couples (Huszar et al., 1992: Fertil Steril 57:882-888).

Pathway of glycogen metabolism in Methanococcus maripaludis

Methanococcus maripaludis, a facultatively autotrophic archaebacterium that grows with H2 or formate as the electron donor, does not assimilate sugars and other complex organic substrates. However, glycogen is biosynthesized intracellularly and commonly reaches values of 0.34% of the cellular dry weight in the early stationary phase. To determine the pathway of glycogen catabolism, specific enzymes of sugar metabolism were assayed in cell extracts. The following enzymes were found (specific activity in milliunits per milligram of protein): glycogen phosphorylase, 4.4; phosphoglucomutase, 10; glucose-6-phosphate isomerase, 9; 6-phosphofructokinase, 5.6, fructose-1,6-bisphosphatase, 10; fructose-1,6-bisphosphate aldolase, 4.2; triosephosphate isomerase, 44; glyceraldehyde-3-phosphate dehydrogenase, 26; phosphoglycerate kinase, 20; phosphoglycerate mutase, 78; enolase, 107; and pyruvate kinase, 4.0. Glyceraldehyde-3-phosphate dehydrogenase was NADP+ dependent, and the pyruvate kinase required MnCl2. The 6-phosphofructokinase had an unusually low pH optimum of 6.0. Four nonoxidative pentose-biosynthetic enzymes were found (specific activity in milliunits per milligram of protein): transketolase, 12; transaldolase, 24; ribulose-5-phosphate-3-epimerase, 55; and ribulose-5-phosphate isomerase, 100. However, the key enzymes of the oxidative pentose phosphate pathway, the reductive pentose phosphate pathway, and the classical and modified Entner-Duodoroff pathways were not detected. Thus, glycogen appears to be catabolized by the Embden-Meyerhoff-Parnas pathway. This result is in striking contrast to the nonmethanogenic archaebacteria that have been examined, among which the Entner-Doudoroff pathway is common. A dithiothreitol-specific NADP(+)-reducing activity was also found (8.5 mU/mg of protein). Other thiol compounds, such as cysteine hydrochloride, reduced glutathione, and 2-mercaptoethanesulfonic acid, did not replace dithiothreitol for this activity. The physiological significance of this activity is not known.

Modulation of allo-immune responses in vivo and in vitro by sperm specific lactate dehydrogenase-C4

The role of sperm specific lactate dehydrogenase-C4 (LDH-C4) in allo-immune responses using mixed lymphocyte cultures (MLC) and cytotoxic T cell (CTL) generation in vitro and local graft versus host (LGVH) reaction and allograft enhancement in vivo has been ascertained. LDH was purified from testes (LDH-C4) and kidney (LDH-B4) of C57Bl/Ks mice. MLC and CTL were performed using C57Bl/Ks-anti A/J lymphocytes in presence of 10(-3)-1 micrograms LDH-B4 or LDH-C4 per culture. The MLC and CTL responses showed biphasic action depending on the dose of LDH-C4. Early MLC culture gave significantly low stimulation index at 10(-2)-10(-1) micrograms LDH-C4 as compared to non-treated control cultures. However, the MLC response in presence of LDH-C4 was not different from the LDH-B4 treated one which showed a similar biphasic trend. On the other hand, 51Cr release from YAC-222 target cells was practically abolished by LDH-C4 at 10(-3)-1(-1) micrograms, and this was strikingly different from LDH-B4 or non-treated cultures. LGVH reactivity as performed by using C57Bl/Ks lymphocytes along with LDH-C4 in (C57Bl/Ks x A/J) F1 hybrids indicated a suppression of stimulation index in primary and secondary (i.e. preimmunized in presence of LDH-C4 or LDH-B4) LGVH. Allograft enhancement of Sa I (A/J) in C57Bl/Ks mice in presence of LDH-C4, was delayed slightly but significantly during primary or secondary transplantation reaction.(ABSTRACT TRUNCATED AT 250 WORDS)

Properties of human testis-specific lactate dehydrogenase expressed from Escherichia coli

The cDNA encoding the C4 isoenzyme of lactate dehydrogenase (LDH-C4) was engineered for expression in Escherichia coli. The Ldh-c open reading frame was constructed as a cassette for production of the native protein. The modified Ldh-c cDNA was subcloned into the prokaryotic expression vector pKK223-3. Transformed E. coli cells were grown to mid-exponential phase, and induced with isopropyl beta-D-thiogalactopyranoside for positive regulation of the tac promoter. Induced cells expressed the 35 kDa subunit, which spontaneously formed the enzymically active 140 kDa tetramer. Human LDH-C4 was purified over 200-fold from litre cultures of cells by AMP and oxamate affinity chromatography to a specific activity of 106 units/mg. The enzyme was inhibited by pyruvate concentrations above 0.3 mM, had a Km for pyruvate of 0.03 mM, a turnover number (nmol of NADH oxidized/mol of LDH-C4 per min at 25 degrees C) of 14,000 and was heat-stable.

Immunization of male but not female mice with the sperm-specific isozyme of lactate dehydrogenase (LDH-C4) impairs fertilization in vivo

The goals of this study were to determine the site at which fertility is impaired in mice immunized with LDH-C4 and to determine whether immunization of both males and females would have a greater antifertility effect than immunization of one sex alone. Mice were immunized with LDH-C4 in two systemic doses in Freund's adjuvants and two gastric doses in bicarbonate buffer. The presence of anti-LDH-C4 antibodies in uterine fluid was confirmed. Male and female mice were assigned to four blocks in which either the males, the females, both, or neither were immunized. Oviducts were viewed directly 1 h after mating for the presence of sperm. No significant effect of immunization on sperm transport to the oviduct could be demonstrated. Fertilization was evaluated 4 h after mating. It was found that immunization of males, but not females, impaired fertilization (19.6% versus 50.8% of the oocytes penetrated in 17 and 19 females, respectively). Orchitis was found histologically in 43.8% of the immunized males and 10% of the control males.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine-resistant, flat-cell PC12 variants having a partial loss of transformed phenotype

We have cloned and characterized two variants of PC12 cells. MPT1 cells were selected by their resistance to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), and variant 2068 was isolated nonselectively as a large, flat-cell variant commonly occurring in PC12 cultures. Variant 2068 cells also exhibit resistance to MPTP. Karyotype analysis revealed that these variants are true derivatives of wild-type PC12 cells; however, each variant is tetraploid, whereas the wild-type parent is diploid. The two variants contain an altered level and composition of lactate dehydrogenase isoenzymes, which could account for a previously described difference in lactate metabolism. Both variants exhibit a partial loss of transformed phenotype in culture in that they are nonrefractile, grow in monolayers, and fail to multiply in soft agar. We suggest that this alteration in transformed phenotype may result in altered mitochondria and lactate dehydrogenase and thus account for their resistance to MPTP. Compared with wild-type PC12 cells, MPT1 cells have a decreased level of fos mRNA and an increased level of myc mRNA; the latter results from an increased level of transcription of exon 1 of the myc gene. Studies with hybrid cells obtained by fusing MPT1 cells with wild-type-like cells show that most, but not all, of the parameters of the MPT1 phenotype predominate.

Phosphotyrosine-containing lactate dehydrogenase is restricted to the nuclei of PC12 pheochromocytoma cells

There are five lactate dehydrogenase (LDH) isoenzymes, composed of various combinations of two types of subunits. LDH-5, which contains only the LDH A subunit, is known to be present in both the cytoplasm and the nucleus, to act as a single-stranded DNA-binding protein possibly functioning in transcription and/or replication, and to undergo phosphorylation of tyrosine 238 in approximately 1% of the enzyme after cell transformation by certain tumor viruses. We have characterized LDH from wild-type PC12 pheochromocytoma cells and from a PC12 variant (MPT1) that exhibits altered lactate metabolism and altered expression of multiple genes. Wild-type and MPT1 cells contain different proportions of LDH isoenzymes, with LDH-5 being more predominant in wild-type cells than in the variant. A small fraction of LDH from PC12 cells contains phosphotyrosine. Approximately 99% of the total LDH activity is located in the cytoplasm, but all of the phosphotyrosine-containing LDH is located in the nucleus. Furthermore, essentially all of the nuclear LDH contains phosphotyrosine. These results suggest that tyrosine phosphorylation can affect its role in the nucleus.

Phosphotyrosine-containing lactate dehydrogenase is restricted to the nuclei of PC12 pheochromocytoma cells

There are five lactate dehydrogenase (LDH) isoenzymes, composed of various combinations of two types of subunits. LDH-5, which contains only the LDH A subunit, is known to be present in both the cytoplasm and the nucleus, to act as a single-stranded DNA-binding protein possibly functioning in transcription and/or replication, and to undergo phosphorylation of tyrosine 238 in approximately 1% of the enzyme after cell transformation by certain tumor viruses. We have characterized LDH from wild-type PC12 pheochromocytoma cells and from a PC12 variant (MPT1) that exhibits altered lactate metabolism and altered expression of multiple genes. Wild-type and MPT1 cells contain different proportions of LDH isoenzymes, with LDH-5 being more predominant in wild-type cells than in the variant. A small fraction of LDH from PC12 cells contains phosphotyrosine. Approximately 99% of the total LDH activity is located in the cytoplasm, but all of the phosphotyrosine-containing LDH is located in the nucleus. Furthermore, essentially all of the nuclear LDH contains phosphotyrosine. These results suggest that tyrosine phosphorylation can affect its role in the nucleus.

The association of type 1, type 2A and type 2B phosphatases with the human T lymphocyte plasma membrane

Several putative plasma-membrane-associated components of the T-lymphocyte signal-transduction pathway are phosphorylated during the initial events of cellular activation. Little is known about the control of dephosphorylation of these components. We have shown by immunoblotting that the type 1 phosphatase, the type 2A phosphatase and type 2B phosphatase (calcineurin) are associated with the plasma membrane of normal human T lymphoblasts and the human T leukaemic cell line Jurkat 6. The type 1 phosphorylase phosphatase activity is present in a latent form which can be stimulated synergistically by deinhibitor and p-nitrophenyl phosphate. The PCSH form of the type 2A phosphatase appears to be the predominant oligomer in the plasma-membrane fraction. All three phosphatases can be extracted from membranes with Nonidet P40, but whereas the type 1c and type 2Ac phosphatases separate into the detergent-poor phase of Triton X-114, calcineurin separates into both detergent-rich and -poor phases. It is probable that one or more of these three plasma-membrane-associated phosphatases play regulatory roles in determining the phosphorylation state of membrane-bound proteins involved in human T-cell activation.

Lactate dehydrogenase from Lampetra planeri is composed of chains of unique type which show intermediate properties between the heart and the muscle isozymes of vertebrates

1. Like other lamprey species, Lampetra planeri displays LDH chains of a single type. Since lampreys are more related to vertebrates than myxines, which do have usual A and B monomers, we suspect that either a gene inactivation or a gene loss occurred in the former group. 2. The characterization of the enzyme gave interesting results. From the standpoint of its affinity for ion exchangers, it behaves as if it is composed of A-type chains. 3. From the standpoint of substrate and product inhibition, it resembles much more closely the B containing isozyme. 4. Since literature reports that the other known single-chained LDH's from lampreys are definitely of the A type, we suggest the possibility that L. planeri enzyme underwent some orthologous evolution which brought it to resemble the heart isozyme.

Biochemical alterations in 7,12-dimethylbenz[a]anthracene-induced mammary tumors from rats subjected to caloric restriction

Caloric restriction reduces the incidence and progression of a broad spectrum of neoplastic diseases, yet little is known about the biochemical and molecular mechanisms involved. Profiles of enzyme activities of importance in cellular energy utilization were examined in 7,12-dimethylbenz[a]anthracene-induced (DMBA) mammary adenocarcinomas from rats fed ad libitum or calorically restricted diets. The diets provided equal nutrients except for fewer carbohydrate-derived calories; graded caloric restriction was 10, 20, 30 and 40%. The specific activities of hexokinase, pyruvate kinase, lactate dehydrogenase, glucose-6-phosphate dehydrogenase, malic enzyme and fructose-1,6-bisphosphatase were all elevated to varying degrees in both large palpable and small, non-palpable tumors from calorically restricted hosts compared to activities in tumors from ad libitum-fed rats. Phosphofructokinase activity was increased in palpable tumors from calorically restricted hosts but markedly reduced in non-palpable tumors. These results suggest adaptive or compensatory alterations in tumor enzyme profiles in response to the altered nutritional state of the host.

Identification of a nucleic acid helix-destabilizing protein from rat liver as lactate dehydrogenase-5

A rat liver DNA helix-destabilizing protein (HDP) that has previously been proposed to play a role in transcription has been identified as M chain lactate dehydrogenase (LDH-5; L-lactate:NAD+ oxidoreductase, EC 1.1.1.27). Tryptic peptides accounting for 157 amino acids in the rat liver HDP have been characterized and then matched to the published sequence for the M chain of porcine LDH. Based on amino acid compositions and direct solid-phase protein sequencing, at least 148 of the 157 residues that were compared are identical in both proteins. In addition, both porcine LDH and the rat liver HDP have blocked amino termini and similar amino acid compositions and molecular weights. Rat liver HDP and LDH-5 that were purified to molecular homogeneity had similar specific activities in both single-stranded DNA (ss DNA) binding and LDH assays. HPLC tryptic peptide maps were also identical for both the rat liver HDP and LDH proteins. Since preincubation of HDP in NADH prevents its binding to ss DNA, both NADH and ss DNA may be binding at the same site. Further support for this latter idea derives from chemical-modification studies which demonstrate that tyrosine-238, which is located near the coenzyme binding site of LDH, seems to be essential for the ability of HDP to bind ss DNA. These results indicate caution in ascribing in vivo roles solely on the basis of binding to ss DNA. Alternatively, they suggest that a single protein may play more than one biological role.

Purification and characterization of the naturally occurring allelic variants of sn-glycerol-3-phosphate dehydrogenase in Drosophila melanogaster

The naturally occurring electrophoretic variants of sn-glycerol-3-phosphate dehydrogenase and a heterodimeric form of the enzyme resulting from a genetic cross of two variant strains of Drosophila were purified to homogeneity by a combination of DEAE-cellulose chromatography and 8-(6-aminohexyl)-amino-ATP-Sepharose affinity chromatography. Each purified protein was compared with respect to a number of physicochemical and kinetic properties. All forms of the enzyme were found to be similar, except for pI differences associated with the electrophoretic variation observed.