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 Cananeia, State of Sao Paulo ranges from 33 to 39. Electrokinetic, kinetic and thermostability propertie s of lactate dehydrogenase (LDH) were tested to determine if individuals wi th 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. T hrough a two-fold serial dilution method applied to 10 different tissues of Mugil sp., a bidirectionally divergent expression of these loci was sugges ted. No association among LDH electrophoretic pattern, thermal inactivation , kinetic responses and different SNS was observed. The apparent K-m(pyr) v alues obtained here were similar to K-m values obtained by other authors fo r muscle and heart LDH or their purified isoforms. The effect of NaCl on K- m and V-max values of Mugil sp. (35 and 39 SNS individuals) indicates that this salt behaves as a competitive inhibitor, since it decreases enzyme-sub strate affinity. Thus, electrokinetic and thermostability behavior, K-m and V-max values and the effect of NaCl do not permit us to consider these mul lets, with SNS ranging from 33 to 39, as belonging to different populations or species.