Temperature-related kinetic differentiation of glucosephosphate isomerase alleloenzymes isolated from the blue mussel,Mytilus edulis

Two glucosephosphate isomerase (GPI;D-glucose-6-phosphate ketolisomerase; EC 5.3.1.9) alleloenzymes from the blue mussel,Mytilus edulis, were purified to homogeneity. The steady-state kinetic properties of GPI1.00 and GPI.96, which exhibit latitudinal clines in frequency along the Atlantic coast of North America, were determined in both the glycolytic and the gluconeogenic reaction directions at physiological temperatures and pH levels. The two alleloenzymes are catalytically similar at low temperatures (5–10°C), while GPI1.00 diverges to become more efficient at higher physiological temperatures (15–25°C). This pattern of differentiation is consistent with the latitudinal distributions of the alleloenzymes and is due to the greater temperature sensitivities of GPI1.00 V max /K m values of the two alleloenzymes are virtually the same over the physiological range of temperatures. The observed pattern of catalytic differentiation is similar to that seen for interspecific GPI variants.