Iodination of mono- and heteroclonal immunoglobulin G with lactoperoxidase and chloramine T.

The difference in the reactivity of tyrosine and histidine residues in mono- and heteroclonal IgG protein toward enzyme catalyzed and chemical iodination has been studied. One heteroclonal and four monoclonal IgG proteins were iodinated using lactoperoxidase or chloramine T. The ratio of the degrees of substitution of the light and the heavy chains varied from IgG to IgG. One of the monoclonal IgG proteins, IgG-Dam, could only be modified in the gamma-chain. The lack of reactivity was attributed to steric hindrance and other local peculiarities. This interpretation is supported by spectrophotometric titration studies.