title: Purification and properties of an NAD(P)+-linked formaldehyde dehydrogenase from Methylococcus capsulatus (Bath).
abstract: Crude soluble extracts of Methylococcus capsulatus strain Bath, grown on methane, were found to contain NAD(P)+-linked formaldehyde dehydrogenase activity. Activity in the extract was lost on dialysis against phosphate buffer, but could be restored by supplementing with inactive, heat-treated extract (70 degrees C for 12 min). The non-dialysable, heat-sensitive component was isolated and purified, and has a molecular weight of about 115000. Sodium dodecyl sulphate gel electrophoresis of the protein suggested there were two equal subunits with molecular weights of 57000. The heat-stable fraction, which was necessary for activity of the heat-sensitive protein, was trypsin-sensitive and presumed to be a low molecular weight protein or peptide. A number of thiol compounds and other common cofactors could not replace the component present in the heat-treated soluble extract. The purified formaldehyde dehydrogenase oxidized three other aldehydes with the following Km values: 0.68 mM (formaldehyde); 0.075 mM (glyoxal); 7.0 mM (glycolaldehyde); and 2.0 mM (DL-glyceraldehyde). NAD+ or NADP+ was required for activity, with Km values of 0.063 and 0.155 mM respectively, and could not be replaced by any of the artificial electron acceptors tested. The enzyme was heat-stable at 45 degrees C for at least 10 min and had temperature and pH optima of 45 degrees C and pH 7.2 respectively. A number of metal-binding agents and substrate analogues were not inhibitory. Thiol reagents gave varying degrees of inhibition, the most potent being p-hydroxymercuribenzoate which at 1 mM gave 100% inhibition. The importance of possessing an NAD(P)+-linked formaldehyde dehydrogenase, with respect to M. capsulatus, is discussed.
mesh_terms: D000445:Aldehyde Oxidoreductases / Q000037:antagonists & inhibitors / Q000302:isolation & purification*; D005557:Formaldehyde; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D008772:Methylococcaceae / Q000187:drug effects / Q000201:enzymology*; D008970:Molecular Weight; D009249:NADP / Q000378:metabolism*; D013379:Substrate Specificity; D013438:Sulfhydryl Compounds / Q000494:pharmacology; D014357:Trypsin / Q000494:pharmacology
chemical_list: D013438:Sulfhydryl Compounds; D005557:Formaldehyde; D009249:NADP; D000445:Aldehyde Oxidoreductases; D014357:Trypsin