Transient-kinetic studies of pig muscle lactate dehydrogenase.
1. The very fast pre-steady-state formation of NADH catalysed by pig M(4) lactate dehydrogenase was equivalent to the enzyme-site concentration at pH values greater than 8.0 and to one-half the site concentration at pH6.8. 2. The rate of dissociation of NADH from the enzyme at pH8.0 (450s(-1)) in the absence of other substrates is faster than the steady-state oxidation of lactate (80s(-1)). The latter process is therefore controlled by a step before NADH dissociation but subsequent to the hydride transfer. 3. The oxidation of enzyme-NADH by excess of pyruvate was studied as a first-order process at pH9.0. There was no effect of NADD on this reaction and it was concluded that the ternary complex undergoes a rate-limiting change before the hydride-transfer step. 4. Some conclusions about the reactions catalysed by the M(4) isoenzyme were drawn from a comparison of these results with those obtained with the H(4) isoenzyme and liver alcohol dehydrogenase.
D000429:Alcohol Oxidoreductases / Q000378:metabolism; D000818:Animals; D006863:Hydrogen-Ion Concentration; D007527:Isoenzymes / Q000378:metabolism; D007700:Kinetics; D007770:L-Lactate Dehydrogenase / Q000378:metabolism*; D008099:Liver / Q000201:enzymology; D009132:Muscles / Q000201:enzymology*; D009243:NAD / Q000378:metabolism; D010084:Oxidation-Reduction; D011773:Pyruvates / Q000378:metabolism; D013552:Swine
D007527:Isoenzymes; D011773:Pyruvates; D009243:NAD; D000429:Alcohol Oxidoreductases; D007770:L-Lactate Dehydrogenase