Genetic control of lactate dehydrogenase expression in mammalian tissues

The amount of lactate dehydrogenase isozyme 4 in erythrocytes of mice is controlled by alleles at the Ldr-1 locus. The A subunits of lactate dehydrogenase from erythrocytes deficient in isozyme 4 cannot assemble in vitro with B subunits to form active isozyme. The inability to form hybrid enzyme is not due to a mutation in the structural gene for the A polypeptide. Rather, a factor that is bound to the A subunits of erythrocytes restricts free exchange with B subunits.