Authentic activity of the ethylene‐forming enzyme observed in membranes obtained from kiwifruit (Actinidia deliciosa)

SUMMARY Membrane vesicles in the juice squeezed from the pericarp of ripe kiwifruit [Actinidia deliciosa (A. Chev.) C. F. Liang & A. R. Ferguson, formerly Actinidia chinensis Planch.] possess an activity of the ethylene‐forming enzyme which showed the essential features of the in vivo enzyme: a preference for the racemic mixture containing the (IR, 2S)‐enantiomer of 1 ‐amino‐2‐ethylcyclopropanc‐ 1 ‐carboxylic acid; a relatively high affinity for the natural substrate 1‐aminocyclopropane‐ 1 ‐carboxylic acid (Km of 125μM); only partial inhibition by excess eatalase and mM concentrations of FDTA, dithiothreitol and ascorbate. During post‐harvest ripening enzyme activity assayed in vitro developed in parallel with enzyme activity assayed in vivo. The kiwifruit enzyme was sensitive to salicylhydroxatnic acid and to a loss of structural integrity of the membrane vesicles. Although only 0·% of the activity measurable in vivo was recovered in vitro. the kiwifruit membranes provide a useful, easily prepared system for studying the ethylene‐forming enzyme in vitro.