EVOLUTIONARY SIGNIFICANCE OF VITAMIN-C BIOSYNTHESIS IN TERRESTRIAL VERTEBRATES

Evolution of vertebrates from aquatic medium to the terrestrial atmosp here containing high concentration of environmental oxygen was accompa nied by tissue-specific expression of the gene for L-gulonolactone oxi dase (LGO). LGO is the terminal enzyme in the pathway of biosynthesis of ascorbic acid in animals. In this paper we present data to indicate that emergence of LGO is apparently to provide the terrestrial verteb rates with adequate amount of ascorbic acid and thereby protect their tissues against oxygen toxicity. Superoxide dismutase (SOD) was not in duced in the early tetrapods. However, SOD activity has increased in t he mammals which is accompanied by a decrease in the LGO activity. In fact, there has been an inverse relationship between LGO and SOD in th e progress of evolution. SOD activity is markedly high in the guinea p ig, flying mammal, monkey and man, the species those lack LGO. The inv erse relationship between LGO and SOD is also observed in rats during postnatal development, that is when the new born rats are exposed to h igh concentration of atmospheric oxygen. Recent results from our labor atory indicate that ascorbic acid is specifically needed for protectio n of microsomal membranes against cytochrome P450-mediated lipid perox idation and protein oxidation, where SOD is ineffective. Data presente d in this paper also indicate an apparent tissue-specific correlation among LGO activity, P450 level and O-2(.-) production during phylogene tic evolution. Copyright (C) 1997 Elsevier Science Inc.