Disulfide crosslinks and the specificity of protein turnover in plants.

Studies of the protein metabolism of detached tomato leaves, hormonally induced to accumulate proteinase inhibitors, have indicated that the state of oxidation of protein-bound half-cystine residues may be a principal parameter affecting in vivo and in vitro stability of leaf proteins. Induced leaves exhibited a general specificity of intracellular protein degradation directed towards the preferential hydrolysis of proteins having free-sulfhydryl residues. Proteins having disulfide cross-linkages, including the proteinase inhibitors, were markedly stable to in vivo degradation, and as a result, accumulated. These results provide a precedence for a cellular protein selection process, resulting from a directed specificity of intracellular protein degradation, which is focused on a particular protein structural parameter.