Electrophoretic pseudopolymorphism: the role of modifications illustrated by proteolysis

The term "pseudopolymorphism" refers to a situation, where there is no simple correspondence between genotype and phenotype: a single genotype may be moulded into several phenotypes. It is known that broad substrate specificity of enzymes may be one of the causes for pseudopolymorphism. This article deals with the other cause for this phenomenon--a consequence of post-translation modifications, such as limited proteolysis. Variability of some enzymes of grass carp Ctenopharyngodon idella Val. (Pisces, Cyprinidae) was studied by gel electrophoresis. It was found that variability of isozyme patterns of lactate dehydrogenase (LDH), glucose-6-phosphate dehydrogenase (G-6-PDH), malic enzyme (ME) and esterase (EST) is connected with the differences in protease activity of grass carp liver homogenates. The fish isozyme patterns of high (and, partially, intermediate) proteinase activity had some anomalies: displacement of fractions, one or several additional fractions, decreased activity of single fractions or the whole spectrum. In some cases, this variability looked like a classical polymorphic system specified by two alleles of one locus. The effect of enzymes' and proteins' modifications on electrophoretical pseudopolymorphism is discussed.