Specificity of S-adenosyl-L-methionine in the inactivation and the labeling of 1-aminocyclopropane-1-carboxylate synthase isolated from tomato fruits.
1-Aminocyclopropane-1-carboxylate (ACC) synthase, which catalyzes the conversion of S-adenosyl-L-methionine (AdoMet) to ACC, is irreversibly inactivated by its substrate AdoMet. AdoMet has two diastereomers with respect to its sulfonium center, (-)-AdoMet and (+)-AdoMet. We prepared (+)- and (-)-AdoMet from a commercial source, and compared their activities as a substrate and as an inactivator of ACC synthase isolated from tomato (Lycopersicon esculentum Mill). fruits. Only (-)-AdoMet produced ACC, whereas both (-)- and (+)-AdoMet inactivated ACC synthase; (+)-AdoMet inactivated the enzyme three times faster than (-)-AdoMet. We have previously shown that ACC synthase was specifically radiolabeled when the enzyme was incubated with S-adenosyl-L-[3,4-14C]methionine. The present results further indicate that S-adenosyl-L-[carboxyl-14C]methionine, but not S-adenosyl-L-[methyl-14C]methionine, radiolabeled the enzyme. These data suggest that the 2-aminobutyric acid portion of AdoMet is linked to ACC synthase during the autoinactivation process. A possible mechanism for ACC synthase inactivation by AdoMet is discussed.
Satoh
S
S
Department of Biological Science, Tohoku University, Sendai, Japan.
Yang
S F
SF
D002384:Catalysis; D002851:Chromatography, High Pressure Liquid; D005638:Fruit / Q000201:enzymology*; D008190:Lyases / Q000037:antagonists & inhibitors* / Q000302:isolation & purification; D012436:S-Adenosylmethionine / Q000494:pharmacology*; D013237:Stereoisomerism; D013379:Substrate Specificity
D012436:S-Adenosylmethionine; D008190:Lyases; C021773:1-aminocyclopropanecarboxylate synthase