proteins are derivitized by reaction of pendant groups , usually groups which are side chains in non - terminal amino acyl units of the protein , in aqueous reactions in the presence of a denaturant . the denaturant is preferably an amphiphilic compound , most preferably an anionic amphiphilic compound such as a long chain alkyl sulphate mono ester , preferably an alkaline metal salt , for instance sodium dodecyl sulphate . the degree of derivatization is increased , while the protein retains activity , such as enzyme activity . the increase in the degree of derivatization enhances the increase in circulation time in vivo and stability on storage and in vivo . preferably the derivatizing reagent is an aldehyde compound which reacts with primary amine groups , generally the epsilon - amino group of lysyl units . derivatization is conducted under reducing conditions to generate a secondary amine derivative .