Developmental genetics of the lactate dehydrogenase isozymes of fish

Three genes (A, B, and E) encoding lactate dehydrogenase (LDH) subunits are shown to be present in fish by: (1) molecular hybridization, (2) allelic variants at two loci, and (3) kinetic, physical, and immunochemical studies. The same studies reveal that the E₄ isozyme is closely related to the B₄ isozyme. The E₄ isozyme is usually synthesized in the regions of the nervous system concerned with vision. However, in some species the E₄ isozyme is found in non‐neural tissues such as lens. The closely related B and E loci tend to simulataneously functional in the same retinal cells. The act of hatching by itself does not appear to act as the stimulus to E gene activation. The E subunit facilitates the assembly of A and B subunits into the same teramer. The developmental and tissue specificity of the function of the LDH E gene suggests that the distinctive physical properties and the kinetic behavior of the LDH E₄ isozyme may play an important role in the metabolism of teleost vision.