The photoreactive arylsulfenyl chlorides 2-nitro-4- azidophenylsulfenyl chloride (2,4-NAPS-Cl) and 2-nitro-5-azidophenylsulfenyl chloride (2,5-NAPS-Cl) have been used for the selective modification of thiol groups in glutathione and [Trp(SH)9]corticotropin (ACTH). Both reagents reacted rapidly with both types of thiol groups to form unsymmetrical disulfides. The photoreactive derivatives of glutathione and [Trp(SH)9]ACTH were stable to neutral and acidic conditions but were readily cleaved above pH 9 and by β-mercaptoethanol. Photolysis of the NAPS derivatives of [Trp(SH)9]-ACTH at neutral pH resulted in the formation of covalently linked polymers and dimers which yielded monomer upon treatment with β-mercaptoethanol. Analysis of the amino acid composition of acid hydrolysates of photolyzed monomeric and dimeric products indicated a decrease in proline, valine, tyrosine, and phenylalanine.
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