Characterization of glycine sarcosine N-methyltransferase and sarcosine dimethylglycine N-methyltransferase.
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.
Nyyssölä
A
A
Helsinki University of Technology, Laboratory of Bioprocess Engineering, FIN-02015 HUT Espoo, Finland. antti.nyyssola@hut.fi
Reinikainen
T
T
Leisola
M
M
D001426:Bacterial Proteins; D001622:Betaine / Q000378:metabolism; D020587:Ectothiorhodospira / Q000201:enzymology* / Q000235:genetics; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics*; D005998:Glycine / Q000378:metabolism; D050938:Glycine N-Methyltransferase; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008780:Methyltransferases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000302:isolation & purification / Q000378:metabolism; D012521:Sarcosine / Q000378:metabolism; D013379:Substrate Specificity; D020245:p-Chloromercuribenzoic Acid / Q000494:pharmacology
D001426:Bacterial Proteins; D004791:Enzyme Inhibitors; D011994:Recombinant Proteins; D001622:Betaine; D020245:p-Chloromercuribenzoic Acid; D008780:Methyltransferases; C433447:sarcosine dimethylglycine methyltransferase, Halorhodospira halochloris; D050938:Glycine N-Methyltransferase; D005998:Glycine; D012521:Sarcosine