Abstract
The copper-catalyzed oxidation of cysteine was followed from the consumption of oxygen using the conventional Warburg method and from the formation of hydrogen peroxide using the spectrophotometric method. The rate of oxygen uptake varied with pH and showed a maximum at pH 7.2. Hydrogen peroxide was produced progressively during the oxidation, which indicated the possibility of the successive four equivalent reduction of oxygen via hydrogen peroxide to water. The amounts of oxygen uptake and of hydrogen peroxide formed decreased with the increase of pH. From the peroxide formation and the oxygen consumption, the mode of the utilization of molecular oxygen was discussed. In the low pH region, the two equivalent redox-reaction, in which oxygen is reduced to hydrogen peroxide, may be predominant. As pH increases, hydrogen peroxide formed is utilized for the reoxidation of copper (I) ion, and thereupon the successivefour equivalent redox-reaction becomes predominant.
