Conversion of 1-aminocyclopropane-1-carboxylic acid to ethylene by isolated vacuoles of Pisum sativum L.

We compared the distribution of 1-aminocyclopropane-1-carboxylic acid (ACC) between the vacuole of isolated pea (Pisum sativum L.) protoplasts and the remainder of the cell and found that over 80% of the ACC was localized in the vacuole. Isolated protoplasts and vacuoles evolved ethylene. Over 80% of the ethylene production by protoplasts could be accounted for as originating from the vacuole. Ethylene synthesis by isolated vacuoles was saturated at ACC concentrations above 1 mM, and the apparent K_m for the conversion of ACC to ethylene was 61 μM. Ethylene production in isolated vacuoles was inhibited by Co²⁺, n-propyl-gallate, in a N₂ atmosphere, and following lysis of the vacuoles. The ethylene-forming enzyme in pea vacuoles exhibited stereospecificity inasmuch as it catalyzed the conversion of (±)-allocoronamic acid to 1-butene but not that of (±)-coronamic acid. The same stereospecificity was also shown by leaf tissue. Based on competition studies with ACC and (±)-allocoronamic acid, we conclude that conversion of ACC to ethylene and (±)-allocoronamic acid to 1-butene is mediated by the same enzyme in isolated vacuoles and in intact leaf tissue. Vacuoles isolated from Vicia faba L. leaves showed essentially the same characteristics with regard to ACC-dependent ethylene synthesis as did pea vacuoles.