Intermediary carbohydrate metabolism of Triatoma infestans (insecta; hemiptera)—I. Glycolytic and pentose phosphate pathway enzymes and the effect of DDT

Abstract

1. (1) Cell-free preparations obtained from thoraces and legs of T. infestans glycolyse glucose, as well as HDP, with the production of pyruvate and α-glycerophosphate in equimolar amounts in the proportion of 1 mole of pyruvate and 1 mole of α-glycerophosphate per mole of glucose utilized. Added HDP is necessary for optimal activity, but the effect of its omission can be partially reversed by increasing the concentration of added ATP. Fluoride is not required for glucose phosphorylation. 2. (2) Cell-free extracts contain enzymes for glycolysis. GAP dehydrogenase is markedly sensitive to iodoacetate and shows appreciable activity in the absence of added l-cysteine. Lactic dehydrogenase activity is negligible, which explains the non-accumulation of lactate as an end-product of glycolysis. 3. (3) The presence of the pentose phosphate pathway in T. infestans is indicated by the presence of several reactions of this pathway in cell-free extracts; 6-PG dehydrogenase and probably G-6-P dehydrogenase appear to be rate-limiting enzymes for carbohydrate degradation through the pentose pathway. 4. (4) The enzyme content of cell-free extracts is related to the developmental stage of the insect and also to the sex. 5. (5) In vivo topically applied DDT (300 μg per specimen) inhibits the glycolytic pyruvate production by cell-free preparations of male and nymph specimens after 22 hr of exposure. Pyruvate production is restored to normal after 48 hr of exposure, but probably some degree of inhibition of α-glycerophosphate production persist in male specimens. This effect is shared by DDE, a non-toxic DDT-analog. 6. (6) Hexokinase, G-6-P dehydrogenase, 6-PG dehydrogenase, aldolase, GAP dehydrogenase, Gly-P dehydrogenase, phosphopyruvic kinase and ribolytic activity are inhibited by DDT in male specimens after 48 hr of exposure to DDT. Phosphopentose isomerase apparently is not inhibited. On the other hand, only G-6-P dehydrogenase and aldolase are inhibited in nymph specimens by DDT.