The Comparative Enzymology of Lactic Dehydrogenases. II. Properties of the Crystalline HM₃ Hybrid from Chicken Muscle and of H₂M₂ Hybrid and H₄ Enzyme from Chicken Liver

The hybrid lactic dehydrogenases H₂M₂ from chicken liver and HM₃ from chicken leg muscle have been isolated and crystallized. The pure H₄ form of the enzyme has been isolated and crystallized from chicken liver and compared to the H₄ obtained from heart. Fingerprint patterns of tryptic digests of the hybrids have been compared to patterns obtained from a 1:1 mixture of the H₄ and M₄ and have shown the hybrids to be a combination of the pure forms. Amino acid analyses, particularly of histidine, place the hybrids at points intermediate between the pure types. The H₄ from chicken liver did not vary significantly in amino acid content or molecular weight from the H₄ obtained from chicken heart. Molecular weights of the hybrids were in the same range as those of the pure types. Heat and time stability studies of the chicken hybrids and of beef hybrids isolated from starch grain have established the intermediate nature of the hybrids. Immunological properties, analog ratios, and oxalate inhibition also demonstrate that the hybrids are combinations of the H₄ and M₄ forms of the enzyme.