Objective:
To understand the role of polyphenol oxidase (PPO) and o-diphenols in plant function, we propose to investigate the biochemical mechanism of o-quinone formation and subsequent interaction (covalent coupling) with plant proteins. The objectives are: 1) determine reaction characteristics of o-quinones with model peptides containing nucleophilic amino acids; 2) determine PPO-generated o-quinone binding characteristics and impact upon metabolic proteins; and 3) determine the potential for PPO systems to cross-link proteins.

Approach:
Initial studies will focus on the use of model peptides to determine the molecular mechanism of PPO-generated o-quinone binding characteristics to specific nucleophilic amino acids and their potential to act on additional PPO substrates. Reactions will be monitored by spectroscopy, liquid chromatography-mass spectrometry (LC-MS), and nuclear magnetic resonance spectrometry (NMR) to determine reaction rates and monitor product formation. Specific proteases as model proteins and a range of o-diphenols will be used to determine the molecular mechanism of PPO-generated quinone binding to and altering metabolic activity of proteins.