Localization of lactate dehydrogenase isozymes in human muscle tissues by the mixed aggregation immunocytochemical technique.

Lactate dehydrogenase (LDH) isozyme composition and localization was determined in sections of skeletal, heart and smooth muscle by the mixed aggregation immunocytochemical method using first antibody directed against purified human LDH-A4 (M4) or LDH-B4 (H4) followed by the enzymes LDH-A4 and LDH-B4, respectively. An even distribution of the two monomers in all fibres was seen with heart muscle and smooth muscle. Heart muscle had a low concentration of A-monomers and a high concentration of B-monomers, whereas the smooth muscle had equal concentrations of the two monomers. In contrast, skeletal muscle from m. quadriceps femoris was found to be composed of two muscle fibre types, one containing mainly A-, the other mainly B-monomers. On the basis of succinate dehydrogenase activity it was shown that the red (type 1) fibres contain mainly B-monomers and the white (type 2) fibres mainly A-monomers of LDH.