Monomeric and Dimeric Forms and the Mechanism-Based Inactivation of 1-Aminocyclopropane-1-Carboxylate Synthase

The molecular mass of 1-aminocyclopropane-1-carboxylate (ACC)synthase from a variety of sources was examined by both high-performancegel-filtration chromatography and polyacryl-amide gel electrophoresisin the presence of sodium dodecylsulfate. Enzymes used wereprepared from wounded or non-wounded pericarp of ripe tomatofruits and wounded mesocarp of winter squash fruits, as wellas from cells of E. coli that had been transformed with cDNAsfor the wound-induced or ripening-induced ACC synthases of tomatoand the wound-induced or auxininduced enzymes from winter squash.The enzymes from tomato fruit tissues were isolated in a monomericform, whereas the enzymes synthesized in E. coli from cDNAsfor tomato ACC synthase were isolated in a dimeric form. ACCsynthases of winter squash obtained either from fruit tissuesor from transformed E. coli cells were isolated in dimeric forms.ACC synthase in the monomeric form was less sensitive to theinactivation that is associated with the catalytic reaction(the mechanism-based inactivation) than the enzyme in the dimericform. A plausible mechanism relating the difference in molecularform to sensitivity to the mechanism-based inactivation of tomatoACC synthase is discussed. (Received February 1, 1993; Accepted May 17, 1993)