Homologies in the active site regions of lactate dehydrogenases

Peptides isolated from several lactate dehydrogenases (EC 1.1.1.27) have been characterized and sequenced. These peptides include much of the substrate binding site as well as the loop of polypeptide chain which shows major conformational changes following coenzyme binding. Despite significant differences in catalytic properties, the amino acid sequence in these two active site regions of the molecule is highly conserved in most cases. A noteable exception is cysteine 165 which at one time was thought to be essential for enzymatic activity. The lactate dehydrogenases investigated were isolated from rabbit muscle, chicken heart, beef heart, and lobster tail.