Role of pyruvate kinase, phosphoenolpyruvate carboxykinase, malic enzyme and lactate dehydrogenase in anaerobic energy metabolism ofTubifex spec

Abstract

1. During anaerobic exposure ofTubifex, lactate and alanine increase only within the first 24 h, while concentrations of succinate, propionate and also acetate continually increase under prevailing anaerobic conditions. Enzymes involved in anaerobic energy metabolism were isolated, and the effects of various metabolites and inorganic compounds on their catalytic properties studied. 2. The specific activities of the cytosolic enzymes LDH, PK, MDH, and PEPCK, and of mitochondrial malic enzyme and MDH are high. 3. Under conditions of high HCO3− (HCO3−+CO2 system), PEPCK is maximally active while PK is inhibited. 4. The catalytic properties of mitochondrial malic enzyme indicate that in vivo this enzyme operates in the direction of malate decarboxylation. 5. The cytosolic oxidoreductases LDH and MDH were examined with regard to the maintenance of redox state. Function of MDH is only subject to substrate availability, while the enzyme-substrate affinity of LDH might be affected by pH to a limited extent. 6. The data support the conclusion that total CO2, fructose-1,6-diphosphate concentration, the adenylate energy charge, and-only to a limited extent-the intracellular pH are regulatory signals which govern PEP metabolism inTubifex.