L-Fucose Metabolism in Mammals. I. Pork Liver L-Fuconate Hydro-lyase

Abstract

Pork liver has been shown to contain a soluble enzyme, L-fuconate hydro-lyase (L-fuconate dehydratase), capable of dehydrating L-fuconate to 2-keto-3-deoxy-L-fuconate. The enzyme has been partially purified. The Km for L-fuconate is 1.0 mM; D-arabonate is also an excellent substrate (Km 1.3 mM) but the enzyme is inactive with D-fuconate, L-arabonate, D-gluconate, D-gulonate, D-galactonate, L-mannonate, and D-glucuronate. The enzyme has a sharp pH optimum at pH 7.0, requires Mg2+ for activity, and is inhibited by p-hydroxymercuribenzoate. The substrate specificity of L-fuconate hydro-lyase resembles that of pork liver L-fucose: NAD oxidoreductase and it is suggested that these enzymes serve in the metabolism of L-fucose by the following pathway: L-fucose → L-fucono-1,5-lactone → L-fuconate → 2-keto-3-deoxy-L-fuconate. The metabolic fate of the latter compound is not known. D-Arabinose can be metabolized by pork liver by an analogous pathway.