Inhibition of the Conversion of 1-Aminocyclopropane-1-carboxylic Acid to Ethylene by Structural Analogs, Inhibitors of Electron Transfer, Uncouplers of Oxidative Phosphorylation, and Free Radical Scavengers

Cyclopropane carboxylic acid (CCA) at 1 to 5 millimolar, unlike related cyclopropane ring analogs of 1-aminocyclopropane-1-carboxylic acid (ACC) which were virtually ineffective, inhibited C(2)H(4) production, and this inhibition was nullified by ACC. Inhibition by CCA is not competitive with ACC since there is a decline, rather than an increase, in native endogenous ACC in the presence of CCA. Similarly, short-chain organic acids from acetic to butyric acid and alpha-aminoisobutyric acid inhibited C(2)H(4) production at 1 to 5 millimolar and lowered endogenous ACC levels. These inhibitions, like that of CCA, were overcome with ACC. Inhibitors of electron transfer and oxidative phosphorylation effectively inhibited ACC conversion to C(2)H(4) in pea and apple tissues. The most potent inhibitors were 2,4-dinitrophenol (DNP) and carbonyl cyanide m-chlorophenylhydrazone (CCCP) which virtually eliminated ACC-stimulated C(2)H(4) production in both tissues. Still other inhibitors of the conversion of ACC to C(2)H(4) were putative free radical scavengers which reduced chemiluminescence in the free radical-activated luminol reaction. These inhibitor studies suggest the involvement of a free radical in the reaction sequence which converts ACC to C(2)H(4). Additionally, the potent inhibition of this reaction by uncouplers of oxidative phosphorylation (DNP and CCCP) suggest the involvement of ATP or the necessity for an intact membrane for C(2)H(4) production from ACC. In the latter case, CCCP may be acting as a proton ionophore to destroy the membrane integrity necessary for C(2)H(4) production.