Photochemical reactions of fentichlor with soluble proteins

The photochemical reactions of the photoallergen fentichlor with soluble proteins have been studied. [35S]Fentichlor was shown to bind covalently to human serum albumin (HSA) when irradiated with UV light (313 nm). HSA had the ability to bind at least eight molecules of fentichlor per molecule of protein. Fractionation of fentichlor-HSA photoadducts after (a) treatment with cyanogen bromide and (b) reduction, carboxymethylation and digestion with trypsin showed that the bound fentichlor was distributed fairly evenly throughout the sequence of the HSA molecule. Fentichlor was also shown to form photoadducts with human gamma-globulin and with bovine insulin. Its binding to insulin was restricted to the B chain of the molecule. Fundamental differences between the photochemical reactions of the photo-allergens fentichlor and tetrachlorosalicylanilide (T4CS) with soluble proteins are discussed. The reactions of fentichlor with soluble proteins are not restricted to specific binding sites (unlike T4CS). Fentichlor has the potential to react photochemically with a wide range of proteins in the epidermis and dermis, to form antigens.