Developmental expression of creatine kinase isozymes in mammalian lens

Abstract

Four different isoforms are thought to comprise the creatine kinase family of enzymes which regulate energy metabolism through the interconversion of ADP and creatine phosphate. In addition to these well characterized isoforms, MM, MB, BB and mitochondrial creatine kinase, several uncharacterized variants with atypical electrophoretic mobility have been described. In mammalian lens, creatine kinase isoforms exhibit both a regional and developmental pattern of expression. In neonatal rat and human lens, the only isoform expressed is a variant cathodic creatine kinase. Near the time of sexual maturation (11–13 yr) there is a dramatic increase in the expression of BB creatine kinase in human lens. In rat lens, a similar pattern of isoenzyme expression is also seen near the time of sexual maturation (5–6 weeks). In the mature rat lens, in addition to the cathodic variant, there is expression of BB and, to a lesser extent, MM creatine kinase. Using a polyclonal antisera, we have localized BB creatine kinase to the cuboidal epithelial cells of the adult rat lens. This unique pattern of isozyme expression and developmental regulation suggests a more complex scheme for the regulation of creatine kinase gene expression than previously postulated.