Identification of the trypsin inhibitor of egg white with ovomucoid.

The trypsin inhibiting action of egg white, which has been known for over 40 years, has not been identified with any of the recognized components (1) of egg white. Suggestions made in this regard include the postulates (a) that difficultly digestible proteins of egg white displaced trypsin from the substrate (casein) (2), (b) that the antitrypsin is associated with the globulin fraction of egg white (3), and (c) that the inhibitor is probably a protein hydrolysis product but not a true protein (4). Balls and Swenson (4), who made the most complete study of the inhibitor, found that it was neither lipide nor carbohydrate (exclusively) and that it had about the same nitrogen content (slightly low), optical rotation, and sulfur content as are now recognized for ovomucoid. Meyer et al. (5) reported that a highly active antitrypsin sample sent them by Dr. Swenson showed the properties and composition of an egg mucoid. They stated that ‘(the inhibitory effect of egg white preparations on tryptic activity is probably due to a mucoid.” However, the activity reported by Balls and Swenson for their best preparation indicated that the inhibitor represented less than 1 per cent of the egg white solids, which, of course, is less than one-tenth of the ovomucoid in egg white. Possible explanation of this result, which conflicts with the results reported in this paper, may lie in the use for assay purposes of enzyme precursors, which were activated by enterokinase, generally in the presence of inhibitor. The complication introduced by the use of precursors and enterokinase (a common practice at the time the work was done) is illustrated by the reports that the inhibitor was an antikinase (6), that it possibly acted by displacing enterokinase from its combination with the enzyme (4), and that the inhibitor was not an antikinase (7, 2). This report concerns a component of egg white that inhibits trypsin containing no enterokinase. Primary consideration is given to data indicating that antitryptic activity is a characteristic of “native” ovomucoid. The considerations include the distribution of the inhibitor in hen’s eggs, preparation and fractional precipitation of the inhibitor, comparison of the