STRUCTURAL DETERMINANTS REQUIRED FOR IDENTIFICATION OF ACC TRANSPORT-RELATED MEMBRANE PROTEINS

Abstract

The ethylene precursor, 1 -aminocyclopropane- 1 -carboxylic acid (ACC), is actively transported across the tonoplast of plant cells, impacting cellular compartmentation of ACC and ethylene biosynthesis. To identify potential photoaffinity probes for identifying ACC transport-related membrane proteins, the effects of over 70 ACC and other amino acid analogs on ACC uptake into isolated maize vacuoles were investigated. Only relatively nonpolar, neutral amino acid stereoisomers of L-configuration were strong inhibitors of ACC transport. Group additions, substitutions, or deletions at the carboxyl, (x-amino and the Pro-(R) methylene, or hydrogen moieties essentially eliminated transport inhibition, whereas side-chain substitutions remained antagonistic. The kinetics of ACC and neutral L-amino acid analogs tested were competitive. The results indicate that the ACC transport system can be classified as a neutral L-amino acid carrier having a relatively high affinity for ACC and other nonpolar amino acids. The results also suggest that the carrier interacts with the carboxyl, alpha-amino, and Pro-(R) groups and the side chain of substrate amino acids. Based on these findings, potential photoaffinity probes of the ACC transport system have been identified.