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Comparison of iodine monochloride and modified chloramine-T radioiodination for in vivo protein studies.

Aggregate formation on gel chromatography and shortened in vivo t1/2 have been shown to result from the usual chloramine-T (CT) radioiodination of proteins. A modified CT method with decreased CT: protein ratio has ben advocated, particularly for use in the 125I-fibrinogen uptake test. In the present study, such modified CT procedures with 131I were assessed by simultaneous injection in rabbits of iodine-125 monochloride protein standards along with the 131I-CT proteins. Standard clearance analyses were performed. For both albumin and fibrinogen a much reduced CT:protein ratio was required before satisfactory in vivo proteins were obtained. The ratio differed for the two proteins, with fibrinogen being more susceptible to CT-induced aggregate formation. Intermediate CT:protein ratios resulted in denaturation of only a portion of the labeled proteins as manifested by a low C1 with a normal t1/2 for the slow component. At intermediate ratios, unaggregated protein displayed abnormal clearance kinetics, indicating that denaturation was not solely the result of aggregates. The results indicated modified CT radioiodination can be used for in vivo studies, but only if carefully compared in vivo with more generally used radiolabeling procedures.