Immunochemical approach to the question of inactive subunits in cases of lactate dehydrogenase B subunit deficiency.

If there were enzymatically inactive B subunits in a solution containing lactate dehydrogenase (LD) B4 prepared from the hemolysates of heterozygous individuals with LD-B subunit deficiency, the inactive subunits would compete with normal subunits for antibodies to the B4 subunit. Using the activity of normal LD-B4 as an index, we could ascertain the proportion of free antigen (LD-B4) and antibody-antigen complexes (LD-B4-anti-LD-B4) and calculate the apparent equilibrium constant, Keq. Doing so, we found the value for Keq in LD-B subunit deficiency to be smaller than that for normal controls. Evidently the expected competitive reaction takes place. We conclude that heterozygous individuals with LD-B subunit deficiency do indeed produce variant (enzymatically inactive) B subunits of LD.