Adenosylmethionine cyclotransferase () is an enzyme that catalyzes the chemical reaction
This enzyme has one substrate, S-adenosyl-L-methionine, which cleaves to give initially L-homoserine lactone and 5'-methylthioadenosine. The lactone is converted to homoserine by spontaneous hydrolysis.
This enzyme was originally described from the yeast Saccharomyces cerevisiae and categorised as a transferase. Later, it was found in bacteriophages and called a hydrolase. However, the bacteriophage enzyme is in fact a lyase with systematic name S-adenosyl-L-methionine lyase.
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