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Reaction of cysteine thiol groups with 1,3-propane sultone: S-3-sulphopropyl as a modifying group for protein chemistry.

Cysteine is smoothly converted to S-3-sulphopropylcysteine by 3-hydroxypropane-sulphonic acid γ-sultone (1,3-propane sultone) in aqueous propanol at pH 8.3. The reaction is about 12 times slower than with iodoacetate but the selectivity for thiol groups is similar, as judged from model experiments and reactions with proteins. S-3-Sulphopropylcysteine is stable to the conditions to total acid hydrolysis and behaves distinctively in electrophoresis and ion-exchange chromatography. Reduction and alkylation of bovine insulin and human serum albumin (pH 8.3, 50% aqueous propanol) on a preparative or analytical scale gives fully S-substituted derivatives. The S-sulphopropylated A and B chains of insulin have been separated by precipitation or ion-exchange chromatography. The sulphopropyl derivatives have good handling properties and the reaction with propane sultone is suggested as a useful addition to the methods of protein chemistry.