Glycerophosphate Bxidase of Flight Muscle Mitochondria

The oxidation of ar-glycerophosphate (glycerol-3-P)’ by tissue preparations was first described by Meyerhof (1). Subsequent studies showed that mammalian tissues contained two types of glycerol-3-P dehydrogenases; one, characterized as a soluble, diphosphopyridine nucleotide-linked enzyme (2, 3) ; the other, as a structurally bound dehydrogenase, not requiring pyridine nucleotide but reacting via the cytochrome system to oxygen (4, 5). Parallel to the situation in vertebrate tissues, both glycerol-3-P oxidase systems were found in insect flight muscle (6-12). Further, the cytological location of these enzymic activities in flight muscle was determined. The DPN requiring dehydrogenase was in the sarcoplasm (8), and the cytochrome-linked dehydrogenase was in the mitochondria (sarcosomes) (6, 10-12). In contradistinction to their status in mammalian muscle, these enzymes were exceptionally active in insect muscle. In fact, recent studies have shown that glycerol-3-P was metabolized by insect mitochondria at a rate 10 to 100 times greater than that of citric acid cycle intermediates (11). The factors influencing this rapid oxidation of glycerol-3-P by flight muscle mitochondria are described in this paper.