Pyruvate ferredoxin oxidoreductase from the hyperthermophilic archaeon, Pyrococcus furious, functions as a CoA-dependent pyruvate decarboxylase

Abstract

Pyruvate ferredoxin oxidoreductase (POR) has been previously purified from the hyperthermophilic archaeon, Pyrococcus furiosus, an organism that grows opti­mally at 100°C by fermenting carbohydrates and peptides. The enzyme contains thiamine pyrophosphate and catalyzes the oxidative decarboxylation of pyruvate to acetyl-CoA and C0₂ and reduces P. furiosus ferredoxin. The authors show that this enzyme also catalyzes the formation of acetaldehyde from pyruvate in a CoA-dependent reaction. Desulfocoenzyme A substituted for CoA showing that the cofactor plays a struc­tural rather than a catalytic role. Ferredoxin was not neces­sary for the pyruvate decarboxylase activity of POR, nor did it inhibit acetaldehyde production. The apparent K_m values for CoA and pyruvate were 0.11 mM and 1.1 mM, respectively, and the optimal temperature for acetaldehyde formation was above 90°C. These data are comparable to those previously determined for the pyruvate oxidation reaction of POR. At 80°C (pH 8.0), the apparent V_m value for pyruvate decarbox­ylation was about 40 percent of the apparent V_m value for pyruvate oxidation rate (using P. furiosus ferredoxin as the electron acceptor). Tentative catalytic mechanisms for these two re­actions are presented. In addition to POR, three other 2-keto acid ferredoxin oxidoreductases are involved in peptide fer­mentation by hyperthermophilic archaea. It is proposed that the various aldehydes produced by these oxidoreductases in vivo are used by two aldehyde-utilizing enzymes, alcohol dehydrogenase and aldehyde ferredoxin oxidoreductase, the physiological roles of which were previously unknown.

Citation

Kesen, Ma; Hutchins, A.; Sung, Shi-Jean S.; Adams, Michael W.W. 1997. Pyruvate ferredoxin oxidoreductase from the hyperthermophilic archaeon, Pyrococcus furious, functions as a CoA-dependent pyruvate decarboxylase. In: Proceedings of theNational Academy of Sciences USA. 94: 9608-9613.