The use of enzyme kinetics to predict differences in cellular metabolism, developmental rate, and swimming performance between LDH-B genotypes of the fish, fundulus heteroclitus.

In summary, the LDH-B4 allelic isozymes of F heteroclitus are functionally nonequivalent. The kinetic differences observed can be explained by a greater catalytic efficiency by LDH-B4b at colder temperatures than LDH-Ba4. The situation appears to be reversed at higher temperatures. The LDH-BaBb allelic isozymes is not exactly intermediate to the two homotetramers. These in vitro functional differences can be interpreted as being useful to individuals with specific LDH-B phenotypes. Moreover, predictions concerning their significance at the metabolic and/or whole organism level can be made and tested experimentally. We have found both developmental and physiological differences between LDH-B phenotypes that appear to depend on a significant variation in ATP metabolism between the phenotypes. Although we have not elucidated the mechanism by which ATP metabolism is affected, we have shown that the pattern of ATP differences between phenotypes, corresponds precisely with the pattern of kinetic differences between the LDH-B allelic isozymes. The resolution of the evolutionary significance of these phenomena and their underlying molecular mechanism will shed light on the controversy between exponents of the selectionist and neutralist schools of thought.