|
L-gulonolactone oxidase (EC (1.1.3.8 )) is an enzyme that produces vitamin C, but is non-functional in Haplorrhini (including humans), in some bats, and in guinea pigs. It catalyzes the reaction of L-gulono-1,4-lactone with oxygen to L-xylo-hex-3-gulonolactone and hydrogen peroxide. It uses FAD as a cofactor. The L-xylo-hex-3-gulonolactone (2-keto-gulono-gamma-lactone) is able to convert to hexuronic acid (ascorbic acid) spontaneously, without enzymatic action. ==Gulonolactone oxidase deficiency== The non-functional gulonolactone oxidase pseudogene (GULOP) was mapped to human chromosome 8p21 that corresponds to an evolutionarily conserved segment on either porcine chromosome 4 (SSC4) or 14 (SSC14).〔(GULOP ) – iHOP〕 GULO produces the precursor to ascorbic acid, which spontaneously converts to the vitamin ("vitamin C"). The loss of activity of the gene for L-gulonolactone oxidase (GULO) has occurred separately in the history of several species. GULO activity has been lost in some species of bats, but others retain it.〔()〕 The loss of this enzyme activity is responsible for the inability of guinea pigs to enzymatically synthesize vitamin C. Both these events happened independently of the loss in the haplorrhini suborder of primates, including humans. The remains of this non-functional gene with many mutations is, however, still present in the genomes of guinea pigs and humans. It is unknown if remains of the gene exist in the bats who lack GULO activity. The function of GULO appears to have been lost several times, and possibly re-acquired, in several lines of passerine birds, where ability to make vitamin C varies from species to species. Loss of GULO activity in the primate order occurred about 63 million years ago, at about the time it split into the suborders Haplorhini (which lost the enzyme activity) and Strepsirrhini (which retained it). The haplorhines ("simple nosed") primates, which cannot make vitamin C enzymatically, include the tarsiers and the simians (apes, monkeys and humans). The strepsirrhines (bent or wet-nosed) primates, which are still able to make vitamin C enzymatically, include lorises, galagos, pottos, and, to some extent, lemurs. L-gulonolactone oxidase deficiency is called "hypoascorbemia"〔(HYPOASCORBEMIA ) – NCBI〕 and is described by OMIM (Online Mendelian Inheritance in Man)〔(OMIM – Online Mendelian Inheritance in Man ) – NCBI〕 as "a ''public'' inborn error of metabolism", as it affects all humans. There exists a wide discrepancy between the amounts of ascorbic acid other primates consume and what is recommended as "reference intakes" for humans. In its patently pathological form, the effects of ascorbate deficiency are manifested as scurvy. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「L-gulonolactone oxidase」の詳細全文を読む スポンサード リンク
|