Effect of an Exposure to Chloramine-T on the Immunoreactivity of Glucagon1

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Abstract
Various preparations of glucagontreated with chloramine-T under different conditionshave been studied with respect to theirimmunoreactivity toward two different glucagonantisera; one specific for pancreatic glucagon andthe other capable of reacting with enteroglucagon aswell. The glucagon preparations exposed to chloramine-T for different periods reacted almost identicallywith the nonspecific antibody whetherthey were used as tracer or standard. On thecontrary, treatment with chloramine-T under severeconditions led to reduced immunoreactivity towardthe specific antibody. Inclusion of dimethyl sulfoxide(DMSO) in the chloramine-T reaction resultedin preservation of the immunoreactivity ofthe treated preparations. The cyanogen bromidecleaved-glucagon, (1-26) homoserine lactone,showed little cross-reactivity with the specific antibodywhereas it reacted to a similar extent with thenonspecific antibody as natural glucagon did. Ami noacid analysis of the hormone exposed tochloramine-T demonstrated that the methionineresidue at position 27 in the glucagon molecule hadbeen oxidized to methionine sulfoxide. In addition,tryptophan had also been affected. DMSO protectedmethionine and tryptophan from the oxidative actionof chloramine-T. We postulate from these results that the change inthe immunoreactivity toward the specific antibodyof glucagon exposed to chloramine-T is mainly dueto oxidation of the methionine residue at position 27in the molecule. The usefulness of DMSO in theiodination process is also discussed. (Endocrinology96: 1254, 1975)

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