title: L-fucose metabolism in mammals. Kinetic studies on pork liver 2-keto-3-deoxy-L-fuconate:NAD+ oxidoreductase.
abstract: Pork liver 2-keto-3-deoxy-L-fuconate:NAD+ oxidoreductase has been shown to convert 2-keto-3-deoxy-L-fuconate to a 6-carbon acid tentatively identified as 2,4(or 5)-diketo-5(or 4)-monohydroxyhexanoate. The enzyme has a pH optimum of 10. 5 or higher. It is stabilized by dithiothereitol and inhibited by p-hydroxymercuribenzoate and heavy metals (Ag+, Hg2+, Co2+, Cd2+, Pb2+, Zn2+, and Cu2+), suggesting the presence of a functionally essential sulfhydryl group; pre-treatment of enzyme with NAD+ prevents inhibition by p-hydrocymercuribenzoate and heavy metals indicating that this sulfhydryl group may be near the NAD+ binding site. The enzyme has an absolute requirement for NAD+; NADP+ is an ineffective coenzyme. Several lines of evidence indicate that the same enzyme acts on both 2-keto-3-deocy-L-fuconate and 2-keto-3-deoxy-D-arabonate; thus, the pure enzyme acts on both substrates, the two substrates have very similar kinetic parameters (Km values are: 2-keto-3-deocy-L-fuconate, 0.20 mM; 2-keto-3-deoxy-D-arabonate, 0.25 mM; NAD+ for either substrate, 0.22 to 0.25 mM), the two substrates show identical pH and temperature profiles and the two substrates compete for common enzyme active sites. A large number of other sugars and sugar acids, including several 2-keto-3-deoxyaldonates, were ineffective as substrates. The dehydrogenase was also found in calf, beef, lamb, mouse, and rat liver. These studies when considered together with previous studies on the metabolism of L-fucose in pork liver indicate the presence of a soluble enzyme pathway capable of converting L-fucose to 2,4(or 5)-diketo-5(or 4)-monohydroxyhexanoate; this pathway can also convert D-arabinose, and probably L-galactose, to the analogous derivatives (diketomonohydroxypentanoate and diketodihydroxyhexanoate, respectively.
mesh_terms: D000429:Alcohol Oxidoreductases / Q000378:metabolism*; D000818:Animals; D002417:Cattle; D005033:Ethylmaleimide / Q000494:pharmacology; D005643:Fucose / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D006902:Hydroxymercuribenzoates / Q000494:pharmacology; D007460:Iodoacetamide / Q000494:pharmacology; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008628:Mercury / Q000494:pharmacology; D051379:Mice; D051381:Rats; D012756:Sheep; D012835:Silver Nitrate / Q000494:pharmacology; D013045:Species Specificity; D013329:Structure-Activity Relationship; D013400:Sugar Acids; D013552:Swine
chemical_list: D006902:Hydroxymercuribenzoates; D013400:Sugar Acids; D005643:Fucose; D012835:Silver Nitrate; D000429:Alcohol Oxidoreductases; D008628:Mercury; D005033:Ethylmaleimide; D007460:Iodoacetamide