[Kinetics of a single proteolysis stem. Proteolysis of ovalbumin]

The course of one-by-one proteolysis of ovalbumin was followed by determining the residual protein. The reactions were found to be of pseudo-first order. The parallel occurring zipper proteolysis had no effect on this result, since it brought about only the splitting of ovalbumin into large fragments without any split-off of TCA-soluble peptides. The one-by-one proteolysis was completed after the protein had been degraded into TCA-soluble peptides; further hydrolysis of the latter proceeded with deceleration. Obeying the pseudo-first order kinetics could not be due to reversible denaturation or local conformational changes preceding the proteolysis. The rate of the one-by-one proteolysis was limited by the rate of splitting of the first peptide bond in the protein molecule; its course could be described the integral form of the Michaelis-Menten equation. The conditions ([S0]/Km values), when the integral form of this equation was practically linear, were determined. It may be suggested that the true concentration of the protein conformers available to the proteolytic attack satisfies these conditions.