Studies on the control of lactate dehydrogenase isoenzyme activity from rat brain by Nad+

Abstract

1. 1. K m values of the five lactate dehydrogenase ( l-lactate : NAD + oxidoreductase, E.G. i. i. i. 27) isoenzymes from rat brain have been determined for l-lactate at a constant NAD + concentration. 2. 2. Kinetic studies of the five isoenzymes have been carried out, when lactate was the variable substrate, with several different concentrations of NAD*. 3. 3. LDH- 2, LDH- 3, LDH- 4, and LDH- 5 are competitively inhibited by NAD+ and the variability of K m increases with the number of A-chains in the tetramer. 4. 4. On the other hand. LDH-i exhibits greater activity at higher NAD* concentrations.