Enzyme activity profiles in an overwintering population of freeze-avoiding gall moth larvae, Epiblema scudderiana

Abstract

The maximal activities of enzymes of intermediary metabolism, notably glycolysis, the hexose monophosphate shunt, and polyol cryoprotectant synthesis were measured over a winter season in freeze-avoiding larvae of the gall moth Epiblema scudderiana. Dynamic changes in enzyme activities were found to reflect metabolic events associated with different and changing requirements of the larvae for survival as winter progressed and ended. Activities of enzymes associated with the cryoprotectant glycerol indicated two possible pathways for its synthesis: (1) glyceraldehyde-phosphate → glyceraldehyde → glycerol via glyceraldehyde phosphatase and NADPH-linked polyol dehydrogenase, or (2) dihydroxyacetonephosphate → glycerol-3-phosphate → glycerol via glycerol-3-phosphate dehydrogenase and glycerol-3-phosphatase. Glycogen phosphorylase activation in the fall supplied carbon equivalents required for glycerol synthesis from glycogen. Hexose monophosphate shunt enzyme activity was high, reflecting the role of this pathway in supplying NAD(P)H for glycerol synthesis. Spring clearance of glycerol appeared to occur via polyol dehydrogenase and glyceraldehyde kinase. Increasing fructose-bisphosphatase activity into late winter and spring was found to increase the gluconeogenic potential needed for cryoprotectant removal. Increased activity of glycerol-3-phosphate dehydrogenase in the spring, possibly reflecting increased α-glycero-phosphate shuttle activity, may be key to the removal of reducing equivalents generated from glycerol removal.