The Estimation of Cathepsin with Hemoglobin and the Partial Purification of Cathepsin

An account of previous work on cathepsin may be found in the monograph of Pozzi (1935). In the hemoglobin method for the estimation of protelnase, denatured hemoglobin is digested and the digestion products not precipitable by trichloracefic acid are estimated colorimetrically. Hemoglobin, unlike commercial casein, edestin, and gelatin, is a reproducible substrate, Only the very first stages of digestion are measured by the tfichloracetic acid method, for only a small amount of digestion is needed to make hemoglobin not precipitable by trichloracetic acid. Thus, only true proteinase is estimated by the hemoglobin method. Almost all the estimations of proteinase recorded in the literature have been made with substrates that are not reproducible. As a result, the values of proteinase activity obtained in different laboratories, or in the same laboratory with different batches of substrate, are not quantitatively comparable. Furthermore, most of the values of proteinase activity recorded, in particular those obtained by the Willst~tter school, were obtained by methods which estimate not proteinase activity alone but the activity of proteinase plus other proteolytic enzymes. As a result, the values obtained by different investigators are not even qualitatively comparable. The hemoglobin-trichloracetic acid method estimates proteinase alone, yields reproducible results, and has now been applied to the four known types of proteinase, pepsin (Anson and Mirsky (1932-33)), trypsin (Anson and Mirsky (1933-34)), papain (Anson (1936-37)), and cathepsin. It would seem desirable that if some other method is used, either independent evidence be given that the method estimates proteinase 565