JBC, Vol. 250, Issue 14, 5470-5474, Jul, 1975
Chemical modification of bovine heart mitochondrial malate dehydrogenase. Selective modification of cysteine and histidine
E. M. Gregory
Bovine mitochondrial malate dehydrogenase (EC 1.1.1.37) was inactivated by
the specific modifications of a single histidine residue upon reaction with
iodoacetamide. NADH protected against this loss of activity and reaction
with the histidine residue, suggesting that the histidine is at the NADH
binding site. N-Ethylmaleimide also modified the enzyme by reacting with 1
sulfhydryl residue. The reaction rate with N-ethylmaleimide was increased
by decreasing the pH from neutrality or by the addition of urea. NADH
protected against the modification of the sulfhydryl group under all the
conditions tested, again suggesting active site specificity for this
inactivation. This enzyme has a subunit weight of 33,000 and is a dimer.
The native malate dehydrogenase will bind only 1 mol of NADH and it is thus
assumed that there is only a single active site per dimer.