The subunits of dogfish M4 lactic dehydrogenase.

Treatment of dogfish l& lactic dehydrogenase with carboxypeptidase A releases 1 mole of phenylalanine per 36,000 g of the enzyme and no other amino acids. A mixture of carboxypeptidases A and B releases 1 mole of phenylalanine and 1 mole of lysine per 36,000 g of the lactic dehydrogenase. The amino terminus of dogfish M4 lactic dehydrogenase does not react with either dansyl chloride or the Edman reagent under dissociating conditions. An acylated amino-terminal peptide, acyl-Thr-Ala-Leu, has been specifically isolated from a subtilisin digest of dogfish M4 lactic dehydrogenase. Amino acid analysis of dogfish M4 lactic dehydrogenase indicates that there are 9 arginine residues per 36,000 g of enzyme. Nine unique arginine peptides have been specifically isolated from a tryptic digest of dogfish Mb lactic dehydrogenase in yields approaching 1 mole of peptide per 36,000 g of digest. It has been concluded from these results that dogfish Mq lactic dehydrogenase is composed of four identical polypeptide chains with a molecular weight of 36,000.