Radioreagent method for the selective determination of cysteine

Liquid-liquid distribution method was applied for the investigation of the complex formation of phenylmercury cation with different amino acids. It was found that the stability constant of phenylmercury cysteinate is eight order higher in comparison with those of phenylmercury complexes with other amino acids which enables to develop a selective radioreagent method for the determination of submicrogram amounts of cysteine. The method is very simple because it consists in a one minute shaking of labelled phenylmercury bromide in an organic solvent with an aqueous sample of cysteine and in the measurement of the radioactivity of the aqueous phase. (author) 5 refs