Properties of the two common electrophoretic variants of phosphoglucomutase in Drosophila melanogaster

Phosphoglucomutase (PGM) of adult stage in Drosophilia melanogaster has been characterized by gel filtration, ion-exchange chromatography, and isoelectric focusing. The two common electrophoretic variants, PGMA and PGMB, differ with respect to their kinetic and stability parameters. PGMA is more thermostable than PGMB but shows the same pH optimum, equal dependence on Mg2+, and identical molecular weight. There is no significant kinetic difference between the two allozymes at the optimum pH values, but at pH 6.0 the Km value for glucose-1,6-diphosphate of PGMB is significantly higher than that of PGMA. This difference might explain the observed selective advantage of the PgmA allele in population studies.