Nonallelic Genes Controlling the Synthesis of Isozymes Which Form Hybrid Patterns

1 Nonallelic Genes Controlling the Synthesis of Isozymes Which Form Hybrid Patterns 

Among these isozymes lactate dehydrogenase (LDH) has been the most carefully studied (Masters and Holmes, 1972). 

The activity of this enzyme gradually decreased during the preimplantation period in mammals, e.g., mouse, which has been genetically well investigated (Brin-ster, 1965 Epstein et al., 1969). After implantation LDH activity increased again 

The LDH-5 fraction predominates in embryonic tissues. Apparently this could be explained physiologically by the fact that LDH-5 can function intensively under anaerobic conditions. This condition is typical for embryonic tissues and for the skeletal muscles. The activity of this enzyme is maximal with pyruvate concentrations that inhibited LDH-1. Apparently, the predominance of LDH-5 affects the rapid conversion of pyruvate to lactate and, therefore, leads to the depletion of oxygen under anaerobic conditions. 

However, in some mammalian skeletal muscles, e.g., m. cambaloideus, an LDH isozyme distribution identical with that found in cardiac muscle was obtained. This could be explained by the fact that these muscles contain mainly red filaments. The primary physiological role of these muscles is to fix the body in a static position and, therefore, they are able to maintain contraction for long periods of time (Wilkinson, 1965). 

---