LDH isozymes in amazon fish—II. Temperature and pH effects on LDH kinetic properties from Mylossoma duriventris and Colossoma macropomum (Serrasalmidae)

Abstract

1. 1. LDH of Mylossoma duriventris and Colossoma macropomum examined by reduction of pyruvate, showed inhibition by low pH (pH 6.0) and activation by high pH (pH 8.5). The optimal pH in this direction was obtained at pH 8.5 and in reverse direction (oxidation of lactate), between pH 9.0 and 10.0. The effect of pH was temperature dependent. 2. 2. The activity of M. duriventris lactate dehydrogenase was increased by high temperatures while the C. macropomum LDH, unlike most vertebrates, was independent of the assay temperature. Also the K m (pyr) values proved to be temperature insensitive in heart muscle LDH from C. macropomun (pH 6.0 and 7.5). 3. 3. Some kinetic parameters, particularly the pyruvate inhibition, expressed as L/H ratios, showed a low divergence between the paralogous LDH loci in both species. 4. 4. The main differences between orthologous isozymes seems to rely on Ldh-B products. This fact corroborates the differences obtained in electrophoretic patterns.