Cathodic Stripping Voltammetric Study of The Release of Inorganic Sulfide from Proteins in Alkaline Media

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Abstract
The concentration of inorganic sulfide ion liberated from a wide range of proteins denatured in 0.2 M NaOH at 25° was measured using cathodic stripping voltammetry (CSV) directly and after separation of the H2S by an isothermal microdiffusion technique. The sulfide produced in 0.2 M NaOH was equivalent to the number of protein disulfide bridges broken, and using several model proteins it was shown that only surface, or solvent-accessible disulfide bonds are attacked. The reaction obeyed first-order kinetics, and the rate was proportional to hydroxide ion concentration. Some simple disulfide compounds were also studied, and possible reaction mechanisms for the formation of sulfide ion are discussed. Normal and cancerous blood serum samples were analysed by CSV measurement of the sulfide released in alkali.