Curves of autoproteolytic acitivity in different organs of the rabbit

Abstract

We have investigated the autoprotcolytic activity of aqueous extraets of rab­bit spleen, livor, kidney, muscle and brain, in a range of froni 2,5 to 10. The extraets have been obtained as detailed in a fonner paper (3), the same as the technical method for proteolytic activity ineasurements, expressed as O.D./100 mg of protein.

In a first series of experiments the auto proteolysis at below 2.5 has been examined, in spleen extraets inactivated and not inactivated by heat. The degree of proteolysis is practically the same in both extracts (fig. 1), which demonstrates the existence of an acid proteolysis. For this reason the rouge of investigated afterwards begius at pH 2.5.

The maximum activity of autoproteolysis has been found in spleen extracts, followed at a much lower level by livor and kidney extracts, and at a very small level by brain and muscle, the latter with a nearly insignificant activity (fig. 2). The optimum has been found at PH 3.5-5.o, but with an activity ran­ge from pH 3.0 to 6.0. This seems to indicate that the autoproteolysis is due to several acid proteinases, and that the curve obtained represents the summation effects of all of tliem. This fact has been clearly shown by Schwabe and Kalnitsky (ii) in the case of catheptic activity of bovine dental pulp, whose optimum activity at 4.0, has been shown integrated by four different cathepsins, with optimum pH at 3.0, 3.5 to 4.5 and 5.0. The broad range of activity for autoproteolysis, contrasts with the sharp end limits obtained in the proteolysis of other protein (3, 11).
In our experimental conditions autoprotcolytic activity over pH 6 has not been appreciated, that’s to say, the exis­tence of a neutral autoproteolysis. Perhaps with a more sensitive method, as is pointed out by Waley and Heyningen (14), the results should be positive. The non existence of autoproteolysis at neutral pH, or at least at a much lower degree than acid autoproteolysis, may be interesting in the discussion of the possible relations between antigen-antibody reaetions and antigen proteolysis.

It is also interesting to note that the maximum autoproteolytic activity is shown in spleen, an immunologically active organ, and after, in the liver and kidney the contribution of which to protein turnover is known. The order of degree in activity that we have found in the rabbit is the same registered by Waley and Heyningen (14) in the ox. The insignificant activity of rabbit muscle is also observed by Snoke and Neu­rath (12), and Koszalka and Miller (7), who suggest that may be due to the existence of an inhibitor or to an excess of substrate.