PYRUVATE FERREDOXIN OXIDOREDUCTASE FROM THE HYPERTHERMOPHILIC ARCHAEON, PYROCOCCUS-FURIOSUS, FUNCTIONS AS A COA-DEPENDENT PYRUVATE DECARBOXYLASE

Pyruvate ferredoxin oxidoreductase (FOR) has been previously purified from the hyperthermophilic archaeon, Pyrococcus furiosus, an organism that grows optimally at 100 degrees C by fermenting carbohydrates and peptides, The enzyme contains thiamine pyrophosphate and catalyzes the oxidative decarboxylation of pyruvate to acetyl-CoA and CO2 and reduc es P. furiosus ferredoxin, Here we show that this enzyme also catalyze s the formation of acetaldehyde from pyruvate in a CoA-dependent react ion, Desulfocoenzyme A substituted for CoA showing that the cofactor p lays a structural rather than a catalytic role, Ferredoxin was not nec essary for the pyruvate decarboxylase activity of FOR, nor did it inhi bit acetaldehyde production, The apparent K-m values for CoA and pyruv ate were 0.11 mM and 1.1 mM, respectively, and the optimal temperature for acetaldehyde formation was above 90 degrees C, These data are com parable to those previously determined for the pyruvate oxidation reac tion of FOR. At 80 degrees C (pH 8.0), the apparent V-m value for pyru vate decarboxylation was about 40% of the apparent V-m value for pyruv ate oxidation rate (using P. furiosus ferredoxin as the electron accep tor), Tentative catalytic mechanisms for these two reactions are prese nted, In addition to FOR, three other 2-keto acid ferredoxin oxidoredu ctases are involved in peptide fermentation by hyperthermophilic archa ea, It is proposed that the various aldehydes produced by these oxidor eductases in vivo are used by two aldehyde utilizing enzymes, alcohol dehydrogenase and aldehyde ferredoxin oxidoreductase, the physiologica l roles of which were previously unknown.