Studies of casein VII. The carbohydrate constitution of glycopeptidic material isolated from enzymic hydrolysates of κ-casein

κ-Casein was hydrolyzed with either crystalline papain (EC 3.4.4.10) or Pronase P. The products of hydrolysis were fractionated by means of ion exchange and Sephadex G-25. A carbohydrate-rich macropeptide isolated from the papain digest contained 4–5 times the quantities of hexose, hexosamine and sialic acid that were present in κ-casein. The concentrations of the three saccharides bore approximately the same ratio to each other in κ-casein as they did in the macropeptide fraction. These results suggested that the carbohydrate part of κ-casein may be a prosthetic group containing hexose, hexosamine and sialic acid in the ratio of 1:1:1. The macropeptide fraction isolated from the Pronase-P hydrolyate contained approximately double the quantity of carbohydrate that was present in the macropeptide isolated from the papain digest.