The presence of (+)-S-adenosyl-L-methionine in the rat brain and its lack of effect on phenylethanolamine N-methyltransferase activity.

(+)-S-Adenosyl-L-methionine [(+)-SAM] was isolated from rat brain and was quantified by HPLC followed by UV spectrophotometric measurements and by 1H-NMR. Its estimated ratio in brain is 3% of total SAM. Because of its commercial unavailability, (+)-SAM was also prepared from chemically synthesized SAM by separation of the two diastereoisomers on a preparative reverse-phase Nucleosil C8 column. The (+) diastereoisomer thus obtained was then assayed in vitro both as an inhibitor and a substrate of phenylethanolamine N-methyltransferase. Enzymatic activity was measured by HPLC analysis. It was shown that (+)-SAM has no effect on phenylethanolamine N-methyltransferase activity; therefore, it is unlikely that (+)-SAM plays any possible role in regulation of adrenaline synthesis in the brain.