A Pulse Radiolysis Study of Zinc(II)—insulin

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Abstract
Reactions of e−aq with zinc(II)—insulin at pH 6·6 and 9·0 yielded relatively low disulphide anion absorptions, suggesting e−aq reacts at other sites than S—S. A similar conclusion was reached for the reaction of CO where an even lower yield of disulphide anion was found. However, here the disulphide anion yield increased with ‘prepulsing’. Simultaneously the rate constant decreased, implying that a more reactive site was ‘cleaned up’. While no reaction of Br with insulin was observed, both OH and Cl reacted rapidly and predominantly at the tyrosine residues. The second order rate constants, calculated in terms of insulin monomer concentrations, are reported for e−aq, CO and Cl. The transient spectra qualitatively support evidence regarding the accessibility of S—S bonds and tryosine residues in the various forms of insulin as predicted from earlier studies.