Formation of guanosine diphosphate L-fucose from guanosine diphosphate D-mannose.

The 6-deoxyhexose, L-fucose, has a wide distribution in nature as a component of bacterial, plant, and animal polysaccharides or oligosaccharides. Its configuration, which is the same as Lgalactose, suggested to earlier workers that it might be formed biosynthetically from n-galactose by reduction of C-l to a methyl group and oxidation of C-6 to an aldehyde. This suggestion was rendered untenable by the demonstration that certain bacteria were able to convert specifically labeled n-glucose-U4 to L-fucose-Cl4 without inversion or cleavage of the carbon chain (l-3). Similar results have recently been reported in man (4). In 1958, a guanosine nucleotide containing fucose, presumably guanosine 5’-diphosphate-L-fucose, was isolated independently from Aerobacter aerogenes (5) and from ewe’s milk (6). An insight into the mechanism for the biosynthesis of L-fucose was subsequently provided by experiments with crude extracts of A. aerogenes in which guanosine 5’-diphosphate-n-mannose was shown to be converted to guanosine 5’-diphosphate-n-fucose (7). This complex conversion required reduced triphosphopyridine nucleotide. The structures of the nucleotides are given in Fig. 1. The present paper is concerned with further evidence for the identity of guanosine 5’-diphosphate-L-fucose as well as preliminary studies on the mechanism of the conversion. Some aspects of this study have been presented (9).