Lactate dehydrogenase binding to the mitochondrial fraction and to a mitochondrial inhibitor as a function of the isoenzymatic composition.

Purified rabbit skeletal muscle LDH M4 isoenzyme, but not H4 isoenzyme, was observed to bind to either the crude mitochondrial fraction or a mitochondrial inhibitor. Several sources of LDH isoenzymes in which M-type subunits with an alkaline pI are predominant bind to this crude mitochondrial fraction and are inhibited by the mitochondrial inhibitor. Binding and inhibition have also been observed with H-type isoenzymes with a pI near 7. The binding and the inhibition processes did not occur with H-type isoenzymes with an acid pI or with M-type isoenzymes with pI near 6. The binding capacity of LDH to the mitochondrial fraction and to the mitochondrial inhibitor is very similar and depends on the net protein charge and not on whether the subunits are H- or M-type.