SUMMARYExtracts of rabies-infected suckling mouse brains purified by precipitation at pH 4"5, freed from smaller antigens by sedimentation at 161, I8og and digested with RNase, DNase and trypsin show in the ultracentrifuge a component of $20 ~ I6 to I8 which is lacking in extracts of normal suckling mouse brains similarly treated. The largest rabies soluble antigen ('outer antigen': Mead, I962b) has a sedimentation constant S~0 ~ I6 estimated by the 'biological' method of Poison & van Regenmortel 0960. The purified antigen appears to consist of rings or possibly single-turn helices about lOO in diameter containing about 0"57/zg. pentose (as ribose) per/zg, total nitrogen. The antigen also appears to contain deoxypentose. It is resistant to pancreatic RNase, DNase, trypsin and chymotrypsin, has a density of about 1.34 g./cma. in CsC1 and an electrophoretic mobility about 7/8 that of rabbit serum albumin at pH 8"5.Preparative density-gradient centrifugation in the analytical rotor of the Model E Spinco centrifuge is described. This allows the method to be applied to smaller particles than can be treated in the S.W. 39 rotor.
1. The preparation of tanned gelatin spheres and granules from high-molecular-weight gelatin is described. This material is comparatively hard, giving high flow rates, is insoluble in water at temperatures between 0 degrees and 100 degrees and is resistant to digestion by trypsin and chymotrypsin. The high-molecular-weight fraction of gelatin was prepared by precipitation with polyethylene glycol, and the spheres and granules prepared from this fraction were hardened and insolubilized by tanning with either formalin or chromium salts or both. 2. The spheres and granules were used successfully for the separation of protein molecules and other protein-aceous materials ranging in molecular weight from 200 to greater than 6000000. This gel exclusion material has several properties superior to those of other products used for similar purposes. Further, it was noticed that the porosity of the spheres differed considerably from that of the granules.
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