INHIBITION BY 1-AMINOCYCLOBUTANE-1-CARBOXYLATE OF THE ACTIVITY OF 1-AMINOCYCLOPROPANE-1-CARBOXYLATE OXIDASE OBTAINED FROM SENESCING PETALS OF CARNATION (DIANTHUS-CARYOPHYLLUS L) FLOWERS

We partially purified 1-aminocyclopropane-1-carboxylate (ACC) oxidase from senescing petals of carnation (Dianthus caryophyllus L. cv. Nora) flowers and investigated its general characteristics, and, in particu lar, the inhibition of its activity by ACC analogs. The enzyme had an optimum pH at 7-7.5 and required Fe2+, ascorbate and NaHCO3 for its ma ximal activity. The K-m for ACC was calculated as 111-125 mu M in the presence of NaHCO3. Its M(r) was estimated to be 35 and 36 kDa by gel- filtration chromatography on HPLC and SDS-PAGE, respectively, indicati ng that the enzyme exists in a monomeric form, These properties were i n agreement with those reported previously with ACC oxidases from diff erent plant tissues including senescing carnation petals. Among six AC C analogs tested, 1-aminocyclobutane-1-carboxylate (ACBC) inhibited mo st severely the activity of ACC oxidase from carnation petals. ACBC ac ted as a competitive inhibitor with the K-l of 20-31 mu M. The compari son between the K-m for ACC and the K-i for ACBC indicated that ACBC h ad an affinity which was ca. 5-fold higher than that of ACC, Whereas A CC inactivated carnation ACC oxidase in a time-dependent manner during incubation, ACBC did not cause the inactivation of the enzyme. Prelim inary experiments showed that ACBC and its N-substituted derivatives d elayed the onset of senescence in cut carnation flowers.