Pseudoisoenzymes of Rabbit Muscle Phosphoglucose Isomerase

Abstract

Abstract Rabbit muscle phosphoglucose isomerase, either in crude muscle extract or after isolation and crystallization, has been found to occur as three different species when chromatographed on carboxymethyl Sephadex. The three forms are indistinguishable with respect to over-all amino acid composition except that they differ in accessibility of their sulfhydryl groups to p-mercuribenzoate. They can be interconverted both by treatment with dithiothreitol and by exposure to oxidative conditions, indicating that they represent different states of the same protein rather than genuinely dissimilar protein species as claimed in another report (Yoshida, A., and Carter, N. D. (1969) Biochim. Biophys. Acta, 194, 151). When subjected to isoelectric focusing, these pseudoisoenzymes yield characteristic isoelectric points which correspond to their elution positions on cation exchange columns.