In addition to their use in the polyurethane and pesticide industries, isocyanates have proven to be useful probes for the exploration of protein structure. This paper focuses on three aspects of isocyanates: their broad reactivity, their reversible interaction with cholinesterases, and the relative hydrolysis rates of alkyl and aryl isocyanates. The broad reactivity of isocyanates as well as the demonstrated affinity labeling of serine and sulfhydryl esterases are discussed. Extension of the affinity labeling studies to include the analysis of the inhibition of cholinesterases by methyl isocyanate shows that methyl isocyanate is not an effective inhibitor of any of the cholinesterases. The inhibition of cholinesterases by alkyl isocyanates shows a pattern of decreased specificity with decreased alkyl chain length. The inhibition of cholinesterases by isocyanates is shown to be reversible, with a maximum rate of reversal seen at physiological pH. This reversal is characteristic of the reaction of an isocyanate with a sulfhydryl group. Finally, the affinity labeling of proteins must compete successfully with the hydrolysis of isocyanates in aqueous solution. The hydrolysis of alkyl isocyanates is shown to be significantly slower than that of the aryl isocyanates.The application of alkyl and aryl isocyanates to the pesticide and polyurethane industries is of major commercial interest worldwide. In addition, the isocyanates have proven to be valuable tools to protein chemists making correlations between protein structure and function. It is the information from these latter studies that may prove valuable to our understanding of how isocyanates affect human and animal populations. As a reagent used for the study of protein structure and function, isocyanates have two major characteristics that make them attractive. First, they are highly reactive with a variety of functional groups found on biological macromolecules, and second, they have a finite lifetime that enables them to react with selected functional groups but not to exist long enough to cause significant, nonspecific modification of the macromolecule under study. It is the purpose of this paper to explore both of these advantages of the isocyanates as protein modification reagents, to summarize information already in the literature, and to present new data relevant to each point. Of particular interest to this symposium will be the comparison of the biochemical results for the aryl isocyanates and the alkyl isocyanates. In the former case, the emphasis will be on toluene diisocyanate (TDI)

No abstract

No abstract