Differences in malate dehydrogenases from the obligately piezophilic deep-sea bacterium Moritella sp strain 2D2 and the psychrophilic bacterium Moritella sp strain 5710

摘要

The gene encoding malate dehydrogenase (MDH) of the obligately piezophilic deep-sea bacterium Moritella sp. strain 2D2 was cloned and sequenced. There were two positions [close to the active site (Ala-180) and in the subunit interaction site (His-229)] with 2D2-specific substitutions. The MDH genes of strain 2D2 and a psychrophilic bacterium Moritella sp. strain 5710 exhibiting the highest sequence similarity were overexpressed in Escherichia coli. The 2D2 MDH was more heat-stable than the 5710 MDH. The apparent K-m value at 62.1 MPa for NADH of the 2132 MDH was higher than that of the 5710 MDH. The 2D2 MDH in which a His-Gln substitution was introduced at position 229 decreased the thermal stability and K-m value at 62.1 MPa. The 57 10 MDH that was substituted Gln-229 with His increased the thermal stability and K-m value at 62.1 MPa. These results indicate that the His residue at position 229 of the 2132 MDH may play a role in the thermal stability and the MDH function at high pressure. (C) 2004 Federation of European Microbiological Societies. Published by Elsevier B.V. All rights reserved.