Keratin polymer containing S-sulphocysteine residues, process for its preparation and the compositions containing it

A process for preparing a polymeric product comprising keratin peptide chains of different molecular weight, said peptide chains being formed of amino acids bonded to one another by amide groups, the amino acid composition of said polymeric product being substantially identical to the amino acid composition of the keratin substance from which said polymeric product is prepared, more than 75 percent of the cysteine linkages of said peptide chains being in the form of S-sulphocysteine, said peptide chains terminating at one end in a free carboxyl group and at their other end in a free amine group, the major part of said peptide chains having a molecular weight from about 1,100 to about 7,500,

• said process comprising converting substantially all the cysteine linkages between the peptide chains of a keratin substance to S-sulphocysteine residues, substantially without forming cysteine residues, by oxidizing sulphitolysis with an aqueous solution of sulfite containing copper or a thionate and enzymatically digesting the resulting keratin substance.