On plastein

Abstract

“Plastein” is the name usually applied to the protein-like substance or substances precipitated from concentrated albumose solutions by the action of enzymes. Of those who have investigated the nature of plasteins, some have agreed that they are resynthesized proteins, resulting from the reversibility of the hydrolytic reaction; others view them merely as albumoses separating from the concentrated solutions because of a lack of proper conditions to maintain solubility; while still others regard them as the insoluble simple products of further digestion of the albumoses.

Because, probably, of the small yields in which plasteins are obtained, no investigator has hitherto performed a systematic estimation of the hydrolytic products, although such estimations furnish at present our most significant data concerning the nature of proteins. We have hydrolyzed 130 g. of plastein obtained by the action of pepsin upon Witte peptone. For comparison we tabulate with our results those obtained by Brunner in Fischer's laboratory from fibrin, the mother protein of the plastein.

Of the thirteen amino-acids tested for in plastein the presence was proved of all except alanine, which was not isolated in pure condition. The proportions otherwise were not greatly different from those found in fibrin. It is evident that the plastein ranks with either the complex native proteins or their higher decomposition products.

In order to obtain evidence indicating with which of the above classes the plastein is to be ranked, viscosity measurements were employed. It has been shown that digestion of a protein solution is accompanied by a rapid decrease in viscosity. Consequently it appears that, under similar conditions, even its primary decomposition products form markedly less viscous solutions than the mother protein.

On comparison of equally concentrated solutions of plastein and fibrin in normal NaOH (400 mg.