The Metabolism of l-Fucose

Abstract

Guanosinediphosphate L-fucose pyrophosphorylase was purified approximately 46-fold from extracts of porcine liver.The purified enzyme was specific for guanosine triphosphate and L-fucose l-phosphate, and exhibited a requirement for magnesium ions.The partially purified pyrophosphorylase preparation was used to prepare an L-fucose-containing nucleotide, which was isolated and characterized as GDP-L-fucose.The preceding paper in this series (1) was concerned with the propert.ies of n-fucose kinase, an enzyme partially purified from porcine liver extract.s that catalyzes the reaction L-fucose + ATP + p-L-fucose l-phosphate + ADP.This enzymatic activity, therefore, could represent the first step in the direct activation of exogenous cfucose.The direct utilization of preformed n-fucose in glycoprotein biosynthesis is implied from the results of Coffey, Miller, and Sellinger (2), who, after the administration of r4C-n-fucose to rats, isolated an acidic mucoprotein from the intestinal mucosa which contained radioactivity only in its n-fucose moiety.By analogy with the known mechanisms of glycosyltransferase, one would predict that the second step in the direct activation of L-fucose would be to form a nucleotide derivative of the sugar, which could then serve as substrate for a fucosyltransferase in the biosynthesis of the glycoproteins.This paper presents evidence for the biosynthesis of guanosine diphosphate n-fucose by a specific pyrophosphorylase which catalyzes the reaction p-n-fucose l-phosphate + GTP + GDP-n-fucose + PPi.This enzyme was purified approximately 46-fold from extracts of porcine liver, and the product of the reaction, GDP-n-fucose, was isolated and characterized.