Genetic variation and relative catalytic efficiencies: lactate dehydrogenase B allozymes of Fundulus heteroclitus.

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Abstract
To evaluate whether functional differences exist between allelic variants of a B type lactate dehydrogenase (LDH; L-lactate:NAD+ oxidoreductase, EC 1.1.1.27) in the teleost fish F. heteroclitus (Linnaeus), the kinetic properties of pyruvate reduction were examined. The pH dependence and the temperature dependence for maximal catalysis were indistinguishable among the allozymes; reaction velocities at low pyruvate concentrations were significantly different. At pH values below 8.00, the LDH-BbBb allozyme showed a greater reaction rate at lower temperatures (e.g., 10.degree. C) than LDH-BaBa. The phenomenon was reversed at higher temperatures (.e.g, > 25.degree. C) for pH values between 6.50-7.00. The rates for the heterozygous phenotype, LDH-Babb, were not the arithmetic average of the 2 homotetrameric allozymes. When reaction rates were compared at constant relative alkalinity, i.e., a constant [OH-]/[H+] ratio, the findings were similar. The differences in the temperature dependence and the pH dependence for pyruvate reduction found between the LDH-B allozymes may reflect a selective adaptation and help explain the geographical variation in the Ldh-b gene frequencies of F. heteroclitus.