Metabolic adaptations to environmental changes in Caenorhabditis elegans

Metabolic adaptations to environmental changes were studied in Caenorhabdit is elegans. To assess adjustments in enzyme function, maximum activities of key enzymes of main metabolic pathways were determined. After a 12 h incub ation at varying temperatures (10, 20 degreesC) and oxygen supplies (normox ia or anoxia), the activities of the following enzymes were determined at t wo measuring temperatures in tissue extracts: lactate dehydrogenase (LDH; a naerobic glycolysis), 3-hydroxyacyl-CoA-dehydrogenase (HCDH; fatty acid oxi dation), isocitrate dehydrogenases (NAD-IDH, NADP-IDH; tricarboxylic acid c ycle) and isocitrate lyase (ICL; glyoxylate cycle). Incubation at 20 degree sC induced a strong increase in maximum LDH activity. Anoxic incubation cau sed maximum HCDH and NADP-IDH activities and, at 10 degreesC incubation, LD H activity to increase. Maximum NAD-IDH and ICL activities were not influen ced by any type of incubation. In order to study the time course of metabol ic adaptations to varying oxygen supplies, relative quantities of free and protein-bound NADH were determined in living C. elegans using time-resolved fluorescence spectroscopy. During several hours of anoxia, free and protei n-bound NADH showed different time courses. One main result was that just a t the moment when the protein-bound NADH had reached a constant level, and the free NADH started to increase rapidly, the worms fell into a rigor stat e. The data on enzyme activity and NADH fluorescence can be interpreted on the basis of a two-stage model of anaerobiosis. (C) 2000 Elsevier Science I nc. All rights reserved.