Zur Frage des „eiweißfreien“ Pepsins

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Abstract
To determine the peptic activity of the substances investigated, 10 cc. casein soln. (6 g. casein + 94 cc. H2O + 6 cc. N NH3, mixture allowed to age 2 days) were placed in the thermostat at 40[degree] for 10 min. and then added to the soln. to be tested, which contained 6 cc. N/5 HCl. The vol. was made up to 25 cc. with N/100 HCl, and the free carboxyl groups in 5 cc. of the mixture detd. by titration with N/10 alcoholic KOH. Crude pepsin soln. was prepared by digesting the minced fundus portion of 20 pig stomachs in 8 1. 0.5% HCl for 30 hrs. at 37[degree]. The mixture was filtered, and the filtrate concd, to 1/3 vol. in vacuo at 25-30[degree]. After aging for some mos. in the ice chest, 1200 cc. of the soln. were adjusted to pH 3.2 with NH3, 800 cc. saturated MgSO4 added, and the soln. left at 0[degree] for 24 hrs. The precipitate formed was separated by centrifugalization and designated I. II was obtained by suspending 30 g. I (moist wt.) in 200 cc. 70% alcohol, shaking the mixture, allowing it to stand 3 hrs. at room temp. and filtering off the insoluble residue (II). The filtrate was kept at[long dash]18[degree] for 24 hrs., and III obtained as a precipitate. I, II and III were called "allopepsins." II and III had activity similar to that of crystalline pepsin prepared by Northrop''s method (J. Gen. Physiol., 13 739, 1930). They were yellowish white powders, soluble in H2O and stable in the dry state. With sulfo-salicylic acid only I gave a true precipitate. The molecular wt. of III, calculated from its tryptophan content, was 6000. Ill probably has a structure similar to peptones.

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