2Vinogradskii Institute of Microbiology, Russian Academy of Sciences, pr. 60-letiya Oktyabrya 7, Build. 2, 117811 Moscow, Russia; fax: (495) 135-6530; E-mail: email@example.com
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Received July 16, 2008; Revision received September 4, 2008
Two isoforms of malate dehydrogenase (MDH), dimeric and tetrameric, have been found in the purple non-sulfur bacterium Rhodobacter sphaeroides strain 2R, devoid of the glyoxylate shunt, which assimilate acetate via the citramalate cycle. Inhibitory analysis showed that the 74-kDa protein is involved in tricarboxylic acid cycle, while the 148-kDa MDH takes part in the citramalate pathway. A single gene encoding synthesis of the isologous subunits of the MDH isoforms was found during molecular-biological investigations. The appearance in the studied bacterium of the tetrameric MDH isoform during growth in the presence of acetate is probably due to the increased level of mdh gene expression, revealed by the real-time PCR, the product of which in cooperation with the citramalate cycle enzymes plays an important role in acetate assimilation.
KEY WORDS: malate dehydrogenase, purification, isoforms, expression regulation