Lactate dehydrogenase of Mugil sp. (Mugilidae, Perciformes). Lack of electrokinetic, thermostability and kinetic differences among individuals with different number of scales

The scale number in lateral sets (SNS) of Mugil sp. (Mugilidae, Perciformes) collected in the lagoon-estuarine region of Cananéia, State of São Paulo ranges from 33 to 39. Electrokinetic, kinetic and thermostability properties of lactate dehydrogenase (LDH) were tested to determine if individuals with different SNS correspond to different species or populations of mullet. As in many other teleosts, LDH-A*, LDH-B*, and LDH-C* loci were detected. Through a two-fold serial dilution method applied to 10 different tissues of Mugil sp., a bidirectionally divergent expression of these loci was suggested. No association among LDH electrophoretic pattern, thermal inactivation, kinetic responses and different SNS was observed. The apparent Km (pyr) values obtained here were similar to Km values obtained by other authors for muscle and heart LDH or their purified isoforms. The effect of NaCl on Km and Vmax values of Mugil sp. (35 and 39 SNS individuals) indicates that this salt behaves as a competitive inhibitor, since it decreases enzyme-substrate affinity. Thus, electrokinetic and thermostability behavior, Km and Vmax values and the effect of NaCl do not permit us to consider these mullets, with SNS ranging from 33 to 39, as belonging to different populations or species

Multiple soluble malate dehydrogenase of Geophagus brasiliensis (Cichlidae, Perciformes)

A recent locus duplication hypothesis for sMDH-B* was proposed to explain the complex electrophoretic pattern of six bands detected for the soluble form of malate dehydrogenase (MDH, EC 1.1.1.37) in 84% of the Geophagus brasiliensis (Cichlidae, Perciformes) analyzed (AB1B2 individuals). Klebe's serial dilutions were carried out in skeletal muscle extracts. B1 and B2 subunits had the same visual end-points, reflecting a nondivergent pattern for these B-duplicated genes. Since there is no evidence of polyploidy in the Cichlidae family, MDH-B* loci must have evolved from regional gene duplication. Tissue specificities, thermostability and kinetic tests resulted in similar responses from both B-isoforms, in both sMDH phenotypes, suggesting that these more recently duplicated loci underwent the same regulatory gene action. Similar results obtained with the two sMDH phenotypes did not show any indication of a six-banded specimen adaptive advantage in subtropical regions