Metabolic relevance of selenium in the insect Corcyra cephalonica. Uptake of 75Se and subcellular distribution.

Requirement, uptake, and subcellular distribution of Na2(75)SeO3 in the larvae of the insect C. cephalonica was investigated. That Se is well tolerated by C. cephalonica upto an added level of 2 ppm in the diet is suggested by the observed increase in body weight, total protein, and succinate dehydrogenase levels. Significant increases in the State 3 respiration ensued with Se supplementation up to 2 ppm in the mitochondrial oxidation of D-glycerol 1-phosphate, succinate and NADH, along with concomitant unaltered State 4 respiration, leading to enhanced RCR values. Maximal uptake of 75Se was registered in the larvae maintained on basal diet when subjected to short-term exposure to 0.5 ppm 75Se level. When exposure level was further increased up to 20 ppm, the observed decrease in the uptake of 75Se suggested that Se status of larvae itself controlled the tissue uptake. Subcellular distribution pattern revealed maximal incorporation of 75Se (cpm/g tissue) in the supernatant fraction, whereas, maximal specific 75Se activity (cpm/mg protein) was associated with the mitochondrial fraction. Autoradiography of the soluble fractions indicated the presence of single selenoprotein in the larval group with short term 2 ppm 75Se exposure. Inherent Se controls both the extent and the nature of distribution of mitochondrial 75Se incorporation. Uptake of 45Ca by the insect mitochondria was enhanced by dietary Se up to 2 ppm but was unaffected by addition of in vitro 75Se in the medium. A more fundamental role for Se in the mitochondrial energy metabolism emerges from these studies.