Clvii. the Phosphorus of Caseinogen. I. Isolation of a Phosphorus-containing Peptone from Tryptic Digests of Caseinogen

THE work described in this paper was commenced in 1924, and a preliminary report issued in the following year [Rimington and Kay, 1925], in which it was stated that from tryptic digests of caseinogen a preparation had been obtained containing amino-acids in association with phosphoric acid, and representing approximately 10 % of the organic phosphorus of the original digest. Since that time, experimental work has been directed along two main lines of approach. In the first place an investigation of the behaviour of caseinogen towards various proteolytic enzymes, phosphatases, acids and alkalis was made [Rimington and Kay, 1926; Rimington, 1927, 1], from which it was possible to draw certain conclusions relative to the state of combination of phosphorus in the caseinogen molecule. The linkage involved appears to be of the ester type, phosphoric acid being united to some hydroxyl-containing constituents of the protein molecule, most probably hydroxyamino-acids. A study of artificially phosphorised proteins [Rimington, 1927, 1] afforded additional evidence in support of this view. At the same time experiments were being continued having as their object the isolation in a pure state of the phosphorus-containing substance present in tryptic digests of caseinogen. This has now been accomplished, and it is with this isolation that the present paper is concerned.