Occurrence of the methylglyoxal bypass in halophilic Archaea

Eight species of halophilic Archaea were tested for the presence of the enzymes of the methylglyoxal bypass. Methylglyoxal synthase was found in extracts of all species tested, with the exception of Halobacterium salinarium and Halobacterium cutirubrum. The enzyme of Haloferax volcanii was most active at pH 7 in the absence of salt, and in the presence of 3 M NaCl or KCl activity was half of that without salt, and was inhibited by phosphate. Glyoxalase I was detected in all species tested. Optimal activity of H. volcanii glyoxalase I was found at pH 7 and 3 M KCl; in the absence of salt, activity was strongly reduced. Glutathione could be replaced by γ-glutamylcysteine as the acceptor of the D-lactoyl group. The work shows that the methylglyoxal bypass may be operative in representatives of the archaeal kingdom.