Thermostability studies on the isozymes of human phosphoglucomutase

SUMMARY 1. A new method for investigating the heat‐stabilities of isozymes is described. Using this method it has been shown that the relative thermostabilities of the isozymes determined by the separate phosphoglucomutase (PGM) loci are PGM2 > PGM1 > PGM3. This conclusion has been confirmed by conventional heat‐stability experiments. 2. No interallelic or intra allelic stability differences were detected between the isozymes determined by the two common alleles PGM12 and PGM21at the PGM1 locus, between PGM12 and PGM22at the second locus or between PGM13 and PGM23 at the third locus. The isozymes determined by a very rare allele (PGM41) appear to be relatively less stable than the isozymes determined by either PGM11or PGM21. 3. Comparison of the PGM isozyme patterns in red cells and other tissues suggests that the in vitro differences in thermostabilities between the isozymes of the separate loci are a true reflexion of the in vivo stabilities of PGM. 4. Promising results obtained with other enzymes suggest that the new method used in the heating experiments on PGM may be a useful general procedure for the investigation of other genetically determined differences in isozyme thermostability.