Pepsin globulin digestion

We found that gastrone activity in human gastric juice is associated with at least two materials (1) carbohydrate of sialomucin, and (2) protein, exhibiting the mobility of y-globulin. It is affected by acid-pepsin digestion, but is retained in some split products of inhibitory materials (K31). The significance of these findings is discussed in Section 8.3. 

Some of the precipitation arcs found on immunoelectrophoresis of gastric juice were considered to be specific products of the gastrointestinal tract. These materials did not represent proteins or their degradation products, since pepsin-digested albumin or Y-globulin yielded no precipitation arcs to the antisera. Some of the precipitation lines (3, 5, 7, and 9) were similar to those found in saliva or bile. 

The spectrophotometric evidence reviewed above for the binding of a proportion of the phenolic hydroxyl groups of the tyrosine residues of native proteins is supported by work on the action of tyrosinase on proteins. Sizer (1946) found that this enzyme oxidizes the tyrosine residues in native trypsin, pepsin, chymotrypsin, casein, peptone, insulin, and hemoglobin. Native ovalbumin, human and bovine serum albumin, tobacco mosaic virus (nucleoprotein), human y- and bovine /3-globulins, and bovine fibrinogen are not susceptible to tyrosinase, but become so after tryptic digestion. It was shown (Sizer, 1947) that for the proteins which are oxidized by tyrosinase in the native state, the observed reaction does indeed occur with the intact proteins and does not require preliminary degradation to tyrosine peptides or free tyrosine. The kinetics of the oxidation of tyrosine by tyrosinase have been studied spectropho-tometrically (Mason, 1948 etc.). 

The experiments of Zunz relate to the products of transformation of egg-albumin, serum-albumin, serum-globulin, as well as casein the first three of these products were in a state of almost absolute purity. The following is the procedure dissolve 2 g. of albuminoid substances in 100 c.c of liquid containing 30 eg. of hydrochloric add and 4 eg. of pepsin. Let it digest at 50°, until a peptone reaction is found. At this point, the hquid is filtered, exactly neutralized, again filtered, and is then acidified with sulphuric add to a dilution of o 75 per cent of the liquid. The salt solution is prepared by saturating in the cold, it has a density of i 450. 

Deutsch, Petermann and Williams (52b) developed a combined pepsin digestion and fractionation lystem to recover half-size y- obulin antibo es from an initial fraction containing jS and y-globulins. The half-rize antibodies give less viscous solutions, and diffuse more rapidly, than the original molecules, and these modified properties may be valuable for clinical use. 

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