Metabolite levels and enzyme activities in Protophormia terranovae during low temperature induced glycerol accumulation

• Published in: Insect biochemistry Vol. 7; no. 2; pp. 141 - 149
• Main Authors: Wood, Frederick E., Mahar, Peter, Nordin, John H.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 1977
• Subjects: MOPS; NADH; TCA; HEPES; EDTA; ADP; ATP
• ISSN: 0020-1790
• DOI: 10.1016/0020-1790(77)90007-5

Certain aspects of metabolic function of the arctic blowfly Protophormia terranovae have been examined to study regulation of low temperature induced glycerol accumulation. In vivo, the steady state concentration of l-glycerol-3-phosphate, elevated sharply in anoxic controls, is unaffected by cold stress. Similarly the ratio of cellular ATP to ADP is not altered by low temperature when compared to that of organisms maintained at room temperature. Because Protophormia continue to respire at low temperatures while glycerol build up occurs ( Wood and Nordin, 1976), the accumulation is not a result of direct blockage of mitochondrial l-glycerol-3-phosphate dehydrogenase or respiration, nor is it due to a depletion of cellular ADP concentrations adversely affecting mitochondrial function. Results of experiments conducted to evaluate temperature effects in vitro on mitochondrial l-glycerol-3-phosphate dehydrogenase and cytochrome oxidase are consistent with the above conclusions. Dialyzed homogenates of Protophormia contain a phosphatase capable of catalyzing the hydrolysis of l-glycerol-3-phosphate. Approximately one third more activity is present in cold stressed organisms compared to room temperature controls but the influence of temperature on catalytic activity per se is not unusual. This argues that the additional phosphatase activity observed in these preparations is expressed during cold stress and is not a result of direct activation of the enzyme(s) at low temperature. Cytoplasmic l-glycerol-3-phosphate dehydrogenase and pyruvate kinase were partially purified from extracts of Protophormia. Their relative activities at low temperature in the presence of physiological concentrations of substrate are also consistent with possible rôles in the glycerol accumulation process.