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Applied and Environmental Microbiology, May 2001, p. 2044-2050, Vol. 67, No. 5
0099-2240/01/$04.00+0   DOI: 10.1128/AEM.67.5.2044-2050.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Characterization of Glycine Sarcosine N-Methyltransferase and Sarcosine Dimethylglycine N-Methyltransferase

Antti Nyyssölä,^1,* Tapani Reinikainen,² and Matti Leisola¹

Helsinki University of Technology, Laboratory of Bioprocess Engineering, FIN-02015 HUT Espoo,¹ and Danisco Cultor Innovation, Sokeritehtaantie 20, FIN-02460 Kantvik,² Finland

Received 10 October 2000/Accepted 19 February 2001

Glycine betaine is accumulated in cells living in high salt concentrations to balance the osmotic pressure. Glycine sarcosine N-methyltransferase (GSMT) and sarcosine dimethylglycine N-methyltransferase (SDMT) of Ectothiorhodospira halochloris catalyze the threefold methylation of glycine to betaine, with S-adenosylmethionine acting as the methyl group donor. These methyltransferases were expressed in Escherichia coli and purified, and some of their enzymatic properties were characterized. Both enzymes had high substrate specificities and pH optima near the physiological pH. No evidence of cofactors was found. The enzymes showed Michaelis-Menten kinetics for their substrates. The apparent K_m and V_max values were determined for all substrates when the other substrate was present in saturating concentrations. Both enzymes were strongly inhibited by the reaction product S-adenosylhomocysteine. Betaine inhibited the methylation reactions only at high concentrations.

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^* Corresponding author. Mailing address: Helsinki University of Technology, Laboratory of Bioprocess Engineering, P.O. Box 6100, FIN-02015, HUT, Finland. Phone: 358-9-4512544. Fax: 358-9-462373. E-mail: antti.nyyssola{at}hut.fi.

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Applied and Environmental Microbiology, May 2001, p. 2044-2050, Vol. 67, No. 5
0099-2240/01/$04.00+0   DOI: 10.1128/AEM.67.5.2044-2050.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

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