Purification and radioimmunoassay of rat lactate dehydrogenase A and B subunits.

We have developed procedures for purifying lactate dehydrogenase isoenzymes from rat tissues that involve two affinity-chromatography steps and that facilitate the isolation of milligram quantities of highly purified proteins within 2--3 days. Antibodies raised against pure A and B subunits in rabbits and hens were used in radioimmunoassays and showed negligible cross-reactivity with heterologous subunits. The radioimmunoassays provide a sensitive method for measuring nanogram amounts of A-subunit and B-subunit polypeptides in tissue homogenates and were employed to characterize the enzyme purification procedures.