Effect of Denaturation on Digestibility of Ovalbumin by Pepsin and Trypsin.

Abstract

The object of this investigation is to throw light on the fundamental mechanism underlying the process of denaturation, by comparing the rates of digestion by pepsin and trypsin of natural ovalbumin with those of the same protein denatured in various ways. Increase in the digestibility of denatured proteins would point to hydrolysis or some other kind of degradation, while decrease in digestibility would indicate a change in the opposite direction.

Crystalline ovalbumin was prepared from egg white and, after dialysis, was used either as such, or after denaturation. The denaturing agents used were acid, alkali, heat, alcohol and shaking. The protein solution was mixed with a calculated amount of acid or alkali, enzyme solution and enough water to make a 1% of protein. A series of such mixtures of varying pH was prepared and maintained at 37.5° C. for a definite length of time, generally 4 hours, at the end of which the enzyme action was quickly stopped, by making the solution either acid or alkali as the case may be. The undigested protein was precipitated with trichloracetic acid and the soluble nitrogen in the filtrate was determined. After making corrections for the nitrogen derived from enzymes the percentage of total nitrogen digested was calculated. The optimal pH and the maximal digestion of the different proteins are shown in Tables I and II.

Summary : (1) In the peptic series the rates of digestion of natural and different forms of denatured proteins are, with a few exceptions, practically the same within the limit of experimental error. This indicates that the fundamental changes underlying denaturation do not affect those linkages in the albumin molecule which are hydrolyzed in peptic digestion. (2) In the tryptic series the rate of digestion of natural albumin is exceeded by all forms of denatured proteins.