OXIDATION OF L-CYSTEINE AND DL-METHIONINE: A COMPARATIVE KINETIC APPROACH

Hemlata Sahu*

Kinetics of oxidation of sulphur containing amino acids Cysteine and Methionine was investigated spectrophotometrically in alkaline medium by Potassium permanganate. The results suggest that oxidation of Cysteine is faster than Methionine, indicating of free thiol (-SH) group is more reactive than thioether(-S-) group of Methionine. Kinetic study emphasizes a significant relation between rate of the oxidation and structure of amino acids. Rate of the reaction is significantly increased by increase in concentration of amino acid and alkali whereas increase in concentration of oxidant does not have significant effect on reaction rate. pH of the medium plays a significant role in oxidation, oxidation rate increases with increase in pH of the medium.There is a good agreement between observed and calculated rate constant. The Arrhenius plot for cysteine oxidation illustrates a strong linear relationship between lnk and 1/T. similar results were obtained for Arrhenius plot of Methionine oxidation. A plausible mechanism has been proposed to account for the reaction results. cystine and Methionine sulphoxide were identified as reaction products by FTIR analysis. L-cystine is a covalently linked dimeric non essential amino acid, required for proper utilization of vitamin B6 and healing of burns, wounds.