ENZYME-ACTIVITY PROFILES IN AN OVERWINTERING POPULATION OF FREEZE-TOLERANT LARVAE OF THE GALL FLY, EUROSTA-SOLIDAGINIS

The activity of some enzymes of intermediary metabolism, including enz ymes of glycolysis, the hexose monophosphate shunt, and polyol cryopro tectant synthesis, were measured in freeze-tolerant Eurosta solidagini s larvae over a winter season and upon entry into pupation. Flexible m etabolic rearrangement was observed concurrently with acclimatization and development. Profiles of enzyme activities related to the metaboli sm of the cryoprotectant glycerol indicated that fall biosynthesis may occur from two possible pathways: 1. glyceraldehyde-phosphate --> gly ceraldehyde --> glycerol, using glyceraldehyde phosphatase and NADPH-l inked polyol dehydrogenase, or 2. dihydroxyacetone-phosphate --> glyce rol-3-phosphate --> glycerol, using glycerol-3-phosphate dehydrogenase and glycerol-3-phosphatase. Clearance of glycerol in the spring appea red to occur by a novel route through the action of polyol dehydrogena se and glyceraldehyde kinase. Profiles of enzyme activities associated with sorbitol metabolism suggested that this polyol cryoprotectant wa s synthesized from glucose-6-phosphate through the action of glucose-6 -phosphatase and NADPH-linked polyol dehydrogenase. Removal of sorbito l in the spring appeared to occur through the action of sorbitol dehyd rogenase and hexokinase. Glycogen phosphorylase activation ensured the required flow of carbon into the synthesis of both glycerol and sorbi tol. Little change was seen in the activity of glycolytic or hexose mo nophosphate shunt enzymes over the winter. Increased activity of the c l-glycerophosphate shuttle in the spring, indicated by greatly increas ed glycerol-3-phosphate dehydrogenase activity, may be key to removal and oxidation of reducing equivalents generated from polyol cryoprotec tant catabolism.