Methionine adenosyltransferase activity

Protection required. Suppose that a mutation in bacteria resulted in diminished activity of methionine adenosyltransferase, the enzyme responsible for the synthesis of SAM from methionine and ATP. Predict how this might affect the stability of the mutated bacteria s DNA. 

S-Adenosyl methionine An important carrier of activated methyl groups. It is formed by the condensation of ATP with the amino acid methionine catalyzed by the enzyme methionine adenosyltransferase in a reaction that releases triphosphate. 

Because of its role in activating methionine for transmethylation, this enzyme was initially called the methionine-activating enzyme. With the later discovery of enzymes which activate the carboxyl group of methionine and other amino acids for protein synthesis, this term became somewhat confusing. In this chapter, the trivial name methionine adenosyltransferase or adenosyhransferase, will be used in accord with the recommendation of the Commission on Enzymes (Enzyme Nomenclature, American Elsevier, New York, 1965). The enzyme has also been called S-adenosylmethionine synthetase. 

Glutamine transaminase from bovine liver, one of the enzymes involved in methionine catabolism, utilizes SeMet as well as methionine (Blazon et al., 1994). However, with some enzymes, differences in the reaction rates for SeMet and Met have been observed. For example, SeMet is a better substrate than Met for the a,7-elimination by L-methionine 7-lyase of Pseudomonas putida (Esaki et al., 1979). The adenosyltransferase from rat liver reacts with L(+)-SeMet at 51% of the rate with L(+)-Met, and with the corresponding d(—) isomers at only 13 and 10% of the rate of L-Met (Pan and Tarver, 1967). The adenosyl transferase from yeast, on the other hand, is more active with SeMet than with Met (Mudd and Cantoni, 1957). This enzyme produces the... 

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