Role of the two types of lactic dehydrogenase

Intracellular compartmentation of cardiac fibres from rainbow trout and Atlantic cod--a general design of heart cells

In mammalian cardiomyocytes, mitochondria and adjacent ATPases with participation of creatine kinase (CK) constitute functional compartments with an exchange of ADP and ATP delimited from cytosolic bulk solution. The question arises if this extends to ectothermic vertebrates: their low body temperature and thinner cardiomyocytes with a lower density of membrane structures may reduce the need and structural basis for compartmentation. In saponin-skinned cardiac fibres from rainbow trout and Atlantic cod, we investigated mitochondrial respiration induced by endogenous ADP generated by ATPases and its competition for this ADP with pyruvate kinase (PK) in excess. At low Ca(2+) activity (pCa = 7.0), PK lowered ATP-induced respiration by 40% in trout and 26% in cod. At high Ca(2+) activity (pCa = 5.41), PK had no effect. Additionally, ADP release from the fibres was almost zero but increased drastically upon inhibition of respiration with 1 mM Na-azide. This suggests that fibres are compartmented. PK abolished creatine-stimulated respiration in trout suggesting a less tight coupling of CK to respiration than in mammals. In conclusion, intracellular compartmentation seems to be a general feature of vertebrate cardiomyocytes, whereas the role of CK is unclear, but it seems to be less important for energy transport in species with lower metabolism.

Effects of hibernation on mitochondrial regulation and metabolic capacities in myocardium of painted turtle (Chrysemys picta)

Painted turtles hibernating during winter may endure long-term exposure to low temperature and anoxia. These two conditions may affect the aerobic capacity of a tissue and might be of particular importance to the cardiac muscle normally highly reliant on aerobic energy production. The present study addressed how hibernation affects respiratory characteristics of mitochondria in situ and the metabolic pattern of turtle myocardium. Painted turtles were acclimated to control (25 degrees C), cold (5 degrees C) normoxic and cold anoxic conditions. In saponin-skinned myocardial fibres, cold acclimation increased mitochondrial respiratory capacity and decreased apparent ADP-affinity. Concomitant anoxia did not affect this. Creatine increased the apparent ADP-affinity to similar values in the three acclimation groups, suggesting a functional coupling of creatine kinase to mitochondrial respiration. As to the metabolic pattern, cold acclimation decreased glycolytic capacity in terms of pyruvate kinase activity and increased lactate dehydrogenase (LHD) activity. Concomitant anoxia counteracted the cold-induced decrease in pyruvate kinase activity and increased creatine kinase activity. In conclusion, cold acclimation seems to increase aerobic and decrease anaerobic energy production capacity in painted turtle myocardium. Importantly, anoxia does not affect the mitochondrial functional integrity but seems to increase the capacity for anaerobic energy production and energy buffering.

Intramitochondrial pyruvate attenuates hydrogen peroxide-induced apoptosis in bovine pulmonary artery endothelium

In the hydrogen peroxide (H2O2) apoptosis model of the murine thymocyte, redox reactant and antioxidant pyruvate prevents programmed cell death. We tested the hypothesis that such protection was mediated, at least in part, via pyruvate handling by mitochondrial metabolism. Cultured bovine pulmonary artery endothelial cells were incubated for 30 min with 0.5 mM H2O2 in the absence and presence of 0.5 mM alpha-cyano-3-hydroxycinnamate, as a selective inhibitor of the mitochondrial pyruvate transporter. In controls H2O2 decreased cell viability by 30% within 24 h; this was associated with apoptosis-like bodies, nuclear condensation, and biochemical DNA damage consistent with programmed cell death. Pyruvate (0.1-20 mM) enhanced cell viability in a dose-dependent manner, with > or = 85% viable cells at > or = 3 mM and no DNA laddering, no positive nick-end labeling (TUNEL), and no detectable Annexin V or propidium iodide staining. In contrast, using > or = 5 mM L-lactate as a cytosolic reductant or acetate as a redox-neutral substrate, cell death increased to approximately 40%, which was associated with intense DNA laddering, positive TUNEL and Hoechst 33258 assays. Alpha-cyano-3-hydroxycinnamate alone did not significantly decrease endothelial viability but reduced viability from 85+/-3 to 71+/-4% (p = 0.023) in presence of 3 mM pyruvate plus H2O2; pathological cell morphology and DNA laddering under the same conditions suggested loss of pyruvate protection against apoptosis. Since alpha-cyano-3-hydroxycinnamate re-distributed medium pyruvate and L-lactate consistent with selective blockade of pyruvate uptake into the mitochondria, the findings support the hypothesis that pyruvate protection against H2O2 apoptosis is mediated in part via the mitochondrial matrix compartment. Possible mediators include anti-apoptotic bcl-2 and/or products of mitochondrial pyruvate metabolism such as citrate that affect metabolic regulation and anti-oxidant status in the cytoplasm.

Changes in lactate dehydrogenase and malate dehydrogenase activities during hypoxia and after temperature acclimation in the armored fish, Rhinelepis strigosa (Siluriformes, Loricariidae)

Lactate (LDH) and malate dehydrogenase (MDH) of white skeletal muscle of fishes acclimated to 20, 25 and 30 degrees C and thereafter submitted to hypoxia were studied in different substrate concentrations. Significant differences for LDH and MDH of white muscle enzyme activities are described here for the first time in Rhinelepis strigosa of fishes acclimated to 20 degrees C and submitted to hypoxia for six hours. LDH presented a significant decrease in enzyme affinity for pyruvate in acute hypoxia, for fishes acclimated to 20 degrees C and an increase for fishes acclimated to 30 degrees C.

A survey on the formation and localization of secondary isozymes in mammalia

A survey on the formation of secondary isozymes (= multiple molecular forms of enzymes) is given by means of well-documented enzyme systems. Further examples of a certain type of formation are summarized in tabular form. Eight different classes of enzyme variants deriving from translational processes are discussed. These are: aggregation, polymerization, oxidation and reduction of free SH groups, limited proteolysis, cleavage of carbohydrate residues, deamidation, noncovalent binding of coenzymes, and conformational isomerism. In addition, the intracellular distribution of secondary isozymes is discussed, as are the formation of artificial enzyme variants and the recognition of multiple enzyme forms caused by an exchange of neutral amino acids. About 200 original papers are cited. The reference list was completed in early 1979.

Parallel evolution of pairs of dehydrogenase isoenzymes

Lactate dehydrogenase and glycerol 3-phosphate dehydrogenase are metabolically coupled by the anaerobic dismutation of glyceraldehyde 3-phosphate and by the NAD redox state. This causes the concentrations of lactate and glycerol 3-phosphate to accumulate proportionally during anaerobic muscle contraction; these concentrations are high relative to those in aerobic tissues such as liver. We show that the isoenzymes of lactate dehydrogenase and glycerol 3-phosphate dehydrogenase from chicken breast muscle have Km values for lactate and glycerol 3-phosphate, respectively, that are 10-fold higher than the Km values measured for the lactate dehydrogenase and glycerol 3-phosphate dehydrogenase isoenzymes from chicken liver. The association of proportionally higher Km values with the potential for proportionally higher accumulation of substrates suggests that the isoenzymes of lactate dehydrogenase and glycerol 3-phosphate dehydrogenase from chicken muscle have evolved in parallel as a coupled metabolic unit distinct from the coupled isoenzymes in liver. The parallelism observed for the reduced substrates extends to the oxidized substrates, and to the coenzymes, NAD+ and NADH.

Lactate dehydrogenase activity and isoenzyme pattern in lungs, erythrocytes, and plasma of ozone-exposed rats and monkeys

The effect of low levels of ozone exposure (8 hr daily for 7 days) on lactate dehydrogenase (LDH) activity and isoenzyme pattern was studied in the lungs, plasma, and erythrocytes of rats and monkeys. Exposure to 0.8 or 0.5 ppm ozone resulted in a significant increase in total LDH activvity in the lungs but not in the plasma and erythrocytes of rats. The LDH-5 fraction of the LDH isoenzymes was significantly decreased in terms of percentage distribution in the lungs and plasma of rats exposed to 0.8 ppm ozone, whereas the LDH-4 in the lungs and plasma and LDH-3 in the lungs were increased. At 0.5 ppm ozone, the isoenzyme distribution was not significantly changed in lungs, plasma, or erythrocytes. In monkeys, no significant change in either total LDH activity or isoenzyme pattern was observed in lungs, plasma, or erythrocytes after exposure to 0.8 ppm ozone.

Histochemistry of lactic dehydrogenase in heart and pectoralis muscles of rat

Left-ventricular heart muscle and pectoralis major muscle of the rat were studied to determine the intracellular localization of lactic dehydrogenase (LDH) isoenzymes. Fixation of tissue for 2 hr in 2% buffered formaldehyde provided the best preservation of the ultrastructure and enzyme activity. Total LDH activity was found diffusely in the ground substance of the sarcoplasm and in the mitochondria of the heart muscle. In skeletal muscle a strong reaction was noted in the sarcoplasmic reticulum, and moderate activity was seen in the ground substance of the sarcoplasm and in the mitochondria. Differentiation of the isoenzymes of LDH was accomplished by addition of 4 M urea or application of heat. Heart-type isoenzymes were mainly localized in the mitochondria and sarcoplasm, whereas muscle-type isoenzymes were localized mainly in the sarcoplasmic reticulum of the skeletal muscle. It is speculated that the sarcoplasmic reticulum of the skeletal muscle is the site of anaerobic glycolysis and that the sarcoplasm and mitochondria are involved primarily in aerobic metabolism of pyruvate.

A comparison of the properties of fructose 1,6-diphosphatase, and the activities of other key enzymes of carbohydrate metabolism, in the livers of embryonic and adult rat, sheep and domestic fowl

1. The activities of some key enzymes of glycolysis and gluconeogenesis were measured in embryonic chick, sheep and rat livers. 2. In chicken the activities of hexokinase, phosphofructokinase and pyruvate kinase are low, but those of glucose 6-phosphatase and fructose diphosphatase are very high; the converse situation exists in the rat (Burch et al. 1963), but in sheep the activities of both phosphofructokinase and fructose diphosphatase are high, and the activities of hexokinase and glucose 6-phosphatase are low. These findings are discussed in relation to carbohydrate metabolism in these embryonic livers. 3. The regulatory properties of fructose diphosphatase from the embryonic livers of these three species were compared with the properties of the enzymes from adult animals. The inhibitions by AMP and fructose diphosphate and the effects of Mg(2+) and pH on the activities of adult and foetal fructose diphosphatase are almost identical. 4. It is concluded that regulatory properties are characteristic of fructose diphosphatase from embryonic and adult tissue, and the importance of this in relation to enzyme development is discussed.

The activities of fructose 1,6-diphosphatase, phosphofructokinase and phosphoenolpyruvate carboxykinase in white muscle and red muscle

1. The activities of fructose 1,6-diphosphatase were measured in extracts of muscles of various physiological function, and compared with the activities of other enzymes including phosphofructokinase, phosphoenolpyruvate carboxykinase and the lactate-dehydrogenase isoenzymes. 2. The activity of phosphofructokinase greatly exceeded that of fructose diphosphatase in all muscles tested, and it is concluded that fructose diphosphatase could not play any significant role in the regulation of fructose 6-phosphate phosphorylation in muscle. 3. Fructose-diphosphatase activity was highest in white muscle and low in red muscle. No activity was detected in heart or a deep-red skeletal muscle, rabbit semitendinosus. 4. The lactate-dehydrogenase isoenzyme ratio (activities at high and low substrate concentration) was measured in various muscles because a low ratio is characteristic of muscles that are more dependent on glycolysis for their energy production. As the ratio decreased the activity of fructose diphosphatase increased, which suggests that highest fructose-diphosphatase activity is found in muscles that depend most on glycolysis. 5. There was a good correlation between the activities of fructose diphosphatase and phosphoenolpyruvate carboxykinase in white muscle, where the activities of these enzymes were similar to those of liver and kidney cortex. However, the activities of pyruvate carboxylase and glucose 6-phosphatase were very low in white muscle, thereby excluding the possibility of gluconeogenesis from pyruvate and lactate. 6. It is suggested that the presence of fructose diphosphatase and phosphoenolpyruvate carboxykinase in white muscle may be related to operation of the alpha-glycerophosphate-dihydroxyacetone phosphate and malate-oxaloacetate cycles in this tissue.

Peafowl lactate dehydrogenase: problem of isoenzyme identification

Peafowl, like other vertebrates, contain multiple forms of lactate dehydrogenase. The electrophoretic properties of the peafowl isoenzymes are unusual in that the isoenzyme from heart tissue can be either more or less anodic than that of muscle, depending on the pH. This finding focuses attention on the problem of isoenzyme identification. It is suggested that isoenzymes be identified on the basis of properties that are chemically and biologically more significant than electrophoretic mobility.

Activities of some enzymes concerned with citrate and glucose metabolism in transplanted rat hepatomas

1. Certain enzymes concerned with citrate and glucose metabolism have been measured in two transplanted rat hepatomas, one induced with ethionine (minimal deviation type) and one induced with dimethylaminoazobenzene. In these hepatomas both citrate-cleavage enzyme and NADP-linked isocitrate dehydrogenase in the soluble fraction of the cell were approximately one-third of the values for normal rat liver. These changes have been discussed in relation to the increased citric acid content of tumours and depressed rate of fatty acid synthesis. 2. The glucose-ATP-phosphotransferase activity was below normal liver values in the ethionine-induced tumour but greater than normal in the dimethylaminoazobenzene-induced hepatoma. The apparent K(m) values for the glucose-ATP phosphotransferases of these hepatomas were approx. 8x10(-5)m; no evidence was found for an enzyme with a high K(m) for glucose equivalent to liver glucokinase. 3. Of the enzymes of the pentose phosphate pathway, glucose 6-phosphate-dehydrogenase activity was three to five times as great whereas 6-phosphogluconate-dehydrogenase activity was the same or lower than normal liver in the ethionine-and dimethylaminoazobenzene-induced tumours respectively.