L-fucose metabolism in mammals. Kinetic studies on pork liver 2-keto-3-deoxy-L-fuconate:NAD+ oxidoreductase

J Biol Chem. 1975 Aug 25;250(16):6191-6.

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

  • Alcohol Oxidoreductases / metabolism*
  • Animals
  • Cattle
  • Ethylmaleimide / pharmacology
  • Fucose / metabolism*
  • Hydrogen-Ion Concentration
  • Hydroxymercuribenzoates / pharmacology
  • Iodoacetamide / pharmacology
  • Kinetics
  • Liver / enzymology*
  • Mercury / pharmacology
  • Mice
  • Rats
  • Sheep
  • Silver Nitrate / pharmacology
  • Species Specificity
  • Structure-Activity Relationship
  • Sugar Acids
  • Swine

Substances

  • Hydroxymercuribenzoates
  • Sugar Acids
  • Fucose
  • Silver Nitrate
  • Alcohol Oxidoreductases
  • Mercury
  • Ethylmaleimide
  • Iodoacetamide