Malate dehydrogenase polymorphism in Amazon Curimatids (Teleostei: Curimatidae): Evidence of an ancient mutational event

Abstract

Electrophoretic mobilities and tissue expression of MDH (malate dehydrogenase) were found to be the same for 12 Curimatidae fish species from the Amazon basin. Similarities in the migration of isozymes produced by sMDH-A* and sMDH-B* allowed no differentiation among these species. Out of 12, six species showed two alleles for sMDH-B*. These alleles, named sMDH-B100* and sMDH-B85*, were present at different frequencies among the six species. B85 and/or B(100/85) phenotypes were generally more thermostable than B100 phenotypes. Based on the occurrence of a single allele (B85*) in six different species, their different frequencies, and their heat inactivation rates, the following hypotheses are suggested: a) the alleles are the result of a single mutational event occurring before the speciation process in this family, or b) they are cryptic alleles, a result of different mutational events.