Biochemical and physiological properties of the lactate dehydrogenase allozymes of the Brazilian teleost, Leporinus friderici, Anostomidae, Cypriniformes

Abstract 1. 1. Lactate dehydrogenase polymorphism of Leporinus friderici is determined by two loci, each one encoded by two alleles—Ldh-A, Ldh-A′ and Ldh-B and Ldh-B′. 2. 2. Biochemical characterization of the different LDH phenotypes was carried out. Substrate saturation curves show that extracts, where the LDH-B predominates, are much more sensitive to substrate inhibition and have higher thermostability than skeletal muscle extracts where the LDH-A predominates. 3. 3. Pyruvate affinity parameters of the different LDH-B phenotypes show differential values in all temperatures assayed. LDH-BB phenotypes presented always greater affinity values than the LDH-BB′ and B′B′ ones. 4. 4. The different LDH-B phenotypes show differential thermostability when tested at 65°C, so, the LDH-B′B′ phenotype had higher stability than the LDH-BB′ and LDH-BB phenotypes. This was corroborated with the isozymes partially purified. 5. 5. A variation was detected in the LDH-B phenotype frequencies since the experiment was started in 1980. 6. 6. All these features suggest that this polymorphism may have an adaptive significance in relation to environmental variability, i.e. temperature fluctuations and water pollution due to industrial waste that notably increased in these last years.