The Reactions of Denatured Egg Albumin with Ferricyanide*

This paper describes the reactions between the reducing groups of denatured egg albumin and ferricyanide. Measurements have been made of the effects on the amount of ferricyanide reduced of varying the time, temperature, and pH of the reaction, and the concentration of ferricyanide; of adding the synthetic detergent, Duponol PC; and of treating the denatured protein before the ferricyanide reaction with formaldehyde and iodoacetamide, which are known to react with SH groups. The main result is that, provided the ferricyanide concentration is not too high and Duponol PC is present, there is a definite reaction between ferricyanide and denatured egg albumin. By a definite ferricyanide reaction is meant one in which the amount of ferricyanide reduced is, within wide limits, independent of the time, temperature, and pH of the reaction, and of the concentration of ferricyanide. For the experiments on protein denaturation for which the definite reaction with ferricyanide was worked out and for many other practical applications of this reaction it is not necessary to know what protein groups reduce dilute ferricyanide in Duponol PC solution or how Duponol PC influences the reaction. The reactions between ferricyanide and various amino acids and proteins which will be described, however, indicate that the new definite reaction between ferricyanide and denatured egg albumin is a reaction with SH groups and that the effect of Duponol PC is to lower the ferricyanide concentration at which the SH groups of denatured egg albumin react with ferricyanide.