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TRYPSIN-RESISTANT phosphopeptones from casein have been studied by Posternak [1927; 1928] and by Rimington [1927, 1, 2]. The former isolated three compounds which he designated 'lactotyrins' and showed them to be made up of 15 to 18 amino-acid units containing serine, glutamic acid, aspartic acid and isoleucine. Posternak's papers contain no experimental details, and although his conclusion that the P in casein exists in the form of phosphoserine has been confirmed by the isolation of this amino-acid by Lipmann [1933], the generally accepted view of the structure of phosphopeptone itself is that advanced by Rimington [cf. Jordan Lloyd & Shore, 1938], according to whom the enzymeresistant polypeptide is made up of 9 hydroxyamino-acid units consisting of 3 mol. of hydroxyglutamic acid, 4 mol. of hydroxyaminobutyric acid and 2 mol. of serine. The discrepancies in the results obtained by these authors and the fact that Harington & Randall [1931] were unable to identify hydroxyglutamic acid as a constituent of casein prompted the reinvestigation of this problem. To obtain a trypsin-resistant phosphopeptone of constant composition advantage was taken of the fact that peptic digestion of casein automatically causes the separation of an insoluble complex, the so-called 'paranuclein', which contains 50-60 % of the P of casein and only about 20 % of its N. After digesting the parannclein till constancy of amino-N was reached, the P-containing complex was precipitated with neutral lead acetate, redigested with trypsin and the phosphopeptone finally separated as the Ba salt insoluble in 50 % alcohol. Preparations so obtained were constant in composition and unaffected by further treatment with trypsin. The amino-N value of 10 % and the atomic N/P ratio of 3-2 to 3-3 indicated a polypeptide of 10 amino-acids attached to 3 phosphoric acid residues. N distribution determined according to Damodaran [1931, 1] gave amide-N values varying from 10 to 13 % in different analyses, dicarboxylic acid-N 43-47 % and monoamino-N 43-45 %, and a complete absence of basic

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Das Verhalten der Titelphosphorverbindung, die als Insektizzid von Bedeutung ist, wird gegenüber Alkalimetallhydroxylaminen mittels kinetischer und absorptionsspektroskopischer Methoden untersucht.

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