Lactate dehydrogenase associated with the mitochondrial fraction and with a mitochondrial inhibitor--II. Enzyme interaction with a mitochondrial inhibitor.

A LDH inhibitor has been isolated from the LDH-free crude mitochondrial fraction of rabbit skeletal muscle. The inhibitor is only released after solubilization of the particle bound enzyme. It only interacts with soluble LDH, since the enzyme bound to the mitochondrial fraction was not inhibited. The inhibitor molecular weight is above 10,000 dalton, it is precipitated by 7.5% trichloroacetic acid or 80% (NH4)2SO4 saturation. It is highly stable to heat and pH variations. The inhibitor only interacts with the enzyme at ionic strengths below 20 mM and at pH 6.0 or less. The kinetic behavior of the inhibited enzyme is non-hyperbolic and is similar to the mitochondrial fraction bound enzyme.