Influence of glycerol on the activity and tetramer-dimer state of lactate dehydrogenase isozymes

1. The effects of glycerol on H4 and M4 isozymes of LDH were studied at 5 degrees C. 2. For H4-LDH, glycerol at 1 or 3% progressively shifted the pyruvate concentration that produced optimal activity to a lower value; glycerol at 1% also markedly increased enzyme relative activity at low enzyme concentration. 3. Correlated with this was a parallel change in H4-LDH dissociation-association as glycerol increased with maximal content of the active dimer found always at the pyruvate concentration producing maximal enzyme activity, and a progressive decrease in dimer content at concentrations of pyruvate that produced substrate inhibition. 4. These experiments confirm the functional importance of dimer-tetramer interconversions in promoting the pyruvate-reducing vs lactate-oxidizing activities of LDH. 5. Glycerol also enhanced enzyme ternary complex formation, elution of H4-LDH from AMP-Sepharose by low concentrations of ADP-ribose increasing in the presence of 1 or 3% glycerol.