Specialized lactate dehydrogenase isozymes: The molecular and genetic basis for the unique eye and liver LDHS of teleost fishes

Electrophoretic and immunochemical analysis of the lactate dehydrogenase isozyme patterns of fishes indicates that these isozymes are the tetrameric products of three LDH loci — A, B, and C — which are present in virtually all teleost fishes. The A and B genes of fishes and their corresponding isozymes have previously been shown to be homologous to the A and B genes of other vertebrates. The eye‐band LDH characteristic of many groups of teleosts, and the liver‐band LDH of gadoid and cyprinid fishes are shown in this report to be encoded in the same LDH locus, designated C. In different groups of fishes this third LDH gene (C) is extremely varied both with regard to its tissue‐specific regulation and with regard to the physical properties of its corresponding subunit. The electrophoretic mobility of the C₄ isozyme ranges from highly anodal in some species to slightly cathodal in others while the mobilities of the A₄ and B₄ tetramers remain relatively constant. Most fish species express the A and B genes for LDH in nearly all tissues. In contrast, the C gene is highly restricted in tissue expression in most advanced teleosts where its isozymic products are found predominantly in the eye of some species or in the liver of others.