Abstract
Starch-gel electrophorsis of the lactate dehydrogenase (LDH) of a cyprinoid fish “mozugo” (Pseudorasbora parva) revealed the presence of one major LDH isozyme system consisting of five isozymes and one additional LDH isozyme present in digestive system and gill. The differences in the electrical charge among the five major isozymes and net negative charge of the most anodal isozyme (LHD-1) were small in marked contrast to the mammalian five LDH isozymes. Subunit-dissociation and recombination tests showed that the five major isozymes are tetramers formed by random association of two subunits, A and B, and homozygote of variant A subunit (Af), which charged more negatively than the normal A subunit, also produce the five possible AfB tetramers. The heterozygote of the variant subunit (Af) and in vitro product of the enzymes of normal and variant homozygote contained only five isozymes, LDH-1 with the same mobility as that in both of the homozygotes and four isozymes with mobility intermediate between the corresponding isozymes of the two homozygotes. The frequency of the three phenotypes of the major LDH isozymes in two population samples followed the Hardy-Weinberg law for two alleles at the A locus. Significant differences in gene frequencies of the A alleles have been found between different populations collected from two isolated lakes. The modification of subunit assembly caused by gene mutation was discussed in connection with the complex patterns of fish LDH.
