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Archaea
Volume 2014, Article ID 349379, 13 pages
http://dx.doi.org/10.1155/2014/349379
Research Article

The Bifunctional Pyruvate Decarboxylase/Pyruvate Ferredoxin Oxidoreductase from Thermococcus guaymasensis

1Department of Biology, University of Waterloo, 200 University Avenue West, Waterloo, ON, Canada N2L 3G1
2Structural Genomics Consortium, University of Toronto, Toronto, ON, Canada M5G 1L7
3Department of Chemistry and Physics, Roger Williams University, One Old Ferry Road, Bristol, RI 02809, USA

Received 15 January 2014; Accepted 29 April 2014; Published 29 May 2014

Academic Editor: William B. Whitman

Copyright © 2014 Mohammad S. Eram et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The hyperthermophilic archaeon Thermococcus guaymasensis produces ethanol as a metabolic end product, and an alcohol dehydrogenase (ADH) catalyzing the reduction of acetaldehyde to ethanol has been purified and characterized. However, the enzyme catalyzing the formation of acetaldehyde has not been identified. In this study an enzyme catalyzing the production of acetaldehyde from pyruvate was purified and characterized from T. guaymasensis under strictly anaerobic conditions. The enzyme had both pyruvate decarboxylase (PDC) and pyruvate ferredoxin oxidoreductase (POR) activities. It was oxygen sensitive, and the optimal temperatures were 85°C and >95°C for the PDC and POR activities, respectively. The purified enzyme had activities of  U mg−1 and  U mg−1, with optimal pH-values of 9.5 and 8.4 for each activity, respectively. Coenzyme A was essential for both activities, although it did not serve as a substrate for the former. Enzyme kinetic parameters were determined separately for each activity. The purified enzyme was a heterotetramer. The sequences of the genes encoding the subunits of the bifunctional PDC/POR were determined. It is predicted that all hyperthermophilic β-keto acids ferredoxin oxidoreductases are bifunctional, catalyzing the activities of nonoxidative and oxidative decarboxylation of the corresponding β-keto acids.