A Mutant A-Type Lactate Dehydrogenase Subunit in Fundulus heteroclitus (Pisces: Cyprinodontidae)

Abstract

The rarity of mutant alleles at the loci coding for the polypeptide subunits of the tetrameric enzyme lactate dehydrogenase (LDH) is emphasized in all vertebrate classes. Fundulus heteroclitus synthesizes three physicochemically distinct types of LDH subunits (A, B and E) under the direction of three genetic loci. Two codominant alleles are present at the B locus which code for the synthesis of two B-type subunits (B and B'). Antisera specific to fish LDH subunits selectively precipitate LDH isozymes from tissue homogenates of F. heteroclitus. Coupled with starch gel electrophoresis and enzyme specific staining techniques, it is possible to determine the LDH isozyme composition of tissues and the genetic interrelationships of the isozymes. Employing this procedure, we have discovered a rare A-locus allele coding for a subunit designated A'. At alkaline pH's, the A' subunit is less negatively charged than the A subunit and migrates more slowly toward the anode. This allele was found only in one out of more than 300 specimens examined. This specimen was an AA' heterozygote.