Molecular basis for the deficiency in humans of gulonolactone oxidase, a key enzyme for ascorbic acid biosynthesis

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Abstract
The inability of humans to synthesize L-ascor-bic acid is known to be due to a lack of L-gulono-γ-lactone oxidase, an enzyme that is required for the biosynthesis of this vitamin. Isolation of a cDNA for rat L-gulono-γ-lactone oxidase allowed us to study the basic defect underlying this deficiency at the gene level and led to isolation of a human genomic clone related to L-gulono-γ-lactone oxidase as well as three overlapping clones covering the entire coding region of the rat L-gulono-γ-lactone oxidase cDNA. Sequence analysis study indicated that the human L-gulono-γ-lactone oxidase gene has accumulated a large number of mutations since it stopped being active and that it now exists as a pseudogene in the human genome.