Enzymic proteolysis

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Abstract
By digestion of "paranuclein" from casein with trypsin an enzyme-resistant phosphopeptone of constant composition was isolated in the form of its Ba salt. The phosphopeptone contained 10 amino-acid units, viz., 3 mol. of glutamic acid. 3 mol. of isoleucine and 4 mol. of serine. The absence of other hydroxy-on dicarboxylic-amino-acids was demonstrated by indirect methods. A method was described for the approx. estimation of serine in the absence of other hydroxyamino acids. The presence of serine in high conc. interfered with the estimation of the dicarboxy-lic acids both by titration and by precipitation according to Foreman, in the former by the formation of secondary acidic decomposition products and in the latter because of the partial precipitation of serine under the same conditions as the dicarboxylic acids.

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