Determination of halfcystine in proteins as cysteine from reducing hydrolyzates.

The separation of cysteine from proline using a variant of the classical cation exchange system for amino acid analysis is described. From reducing hydrolyzates (6 M HCl/0.1% phenol/5% thioglycollic acid, 18 h, 110 degrees C) the halfcystine content of proteins can be accurately determined as cysteine. The system is useful for routine determination of the composition of proteins from a single type of hydrolyzate.