Yeong-Biau Yu, Douglas O. Adams, Shangfa Yang
Nov 1, 1979
Citations
5
Influential Citations
329
Citations
Quality indicators
Journal
Archives of biochemistry and biophysics
Abstract
Abstract 1-Aminocyclopropanecarboxylate (ACC) synthase, which catalyzes the conversion of S -adenosylmethionine (SAM) to ACC and methylthioadenosine, was demonstrated in tomato extract. Methylthioadenosine was then rapidly hydrolyzed to methylthioribose by a nucleosidase present in the extract. ACC synthase had an optimum pH of 8.5, and a K m of 20 μ m with respect to SAM. S -Adenosylethionine also served as a substrate for ACC synthase, but at a lower efficiency than that of SAM. Since S -adenosylethionine had a higher affinity for the enzyme than SAM, it inhibited the reaction of SAM when both were present. S -Adenosylhomocysteine was, however, an inactive substrate. The enzyme was activated by pyridoxal phosphate at a concentration of 0.1 μ m or higher, and competitively inhibited by aminoethoxyvinylglycine and aminooxyacetic acid, which are known to inhibit pyridoxal phosphate-mediated enzymic reactions. These results support the view that ACC synthase is a pyridoxal enzyme. The biochemical role of pyridoxal phosphate is catalyzing the formation of ACC by α,γ-elimination of SAM is discussed.