Three phenotypes of glucosephosphate isomerase in sheep: improved staining recipe

Contrary to results published recently, we observe three, rather than two, phenotypes for the enzyme glucosephosphate isomerase (EC 5.3.1.9) from sheep. The phenotypic electro phoretic patterns conform to the patterns observed for this dimeric enzyme in other species. Genotype frequencies in a flock of South downs do not deviate significantly from those predicted under the assumption of the Hardy-Weinberg equilibrium. A remarkable observation is that the electro phoretically distinct phenotypes of GPI are largely or entirely obliterated by the addition of 1–10 mmol/1 MgCl₂ to the electro phoretic buffers. Modification of the usual staining recipe for GPI result in greater resolution and shorter staining times.