✍ Scribed by Dr. P. Jollès
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Casein from cow's milk is not a single substance, but can be resolved into numerous components. These include x-casein, which is the only fraction that contains appreciable quantities of sugars. This component prays a very important role in the clotting of milk by rennin, when it is split into an almost sugar-free fraction, para-x-casein, and a fraction containing sugars, x-caseinoglycopeptide. Caseinoglycopeptides have been isolated not only from the casein of cow's milk, but also from the caseins of sheep, goat, and human milk. The second part of the paper deals with the clotting of milk by rennin and the amino acid sequence in caseinoglycopeptides.
The proteins in milk belong to two groups: phosphoproteins or caseins (78 % in cow's milk), which are insoluble in acidic media, and milk serum proteins (17%), i.e. p-lactoglobulin, oc-lactalbumin, globulins, serum albumins, etc. 5 % of the substances are non protein nitrogen (NPN) containing components such as peptides. In this paper, the percentages indicated are percentages of the dry substances (by weight).
A. Casein from Cow's Milk
Casein from cow's milk is one of the few substances isolated and studied as early as the first half of the 19th century 11-53. It was later found [6-91 that casein is not a pure substance. Studies of solubility in dilute hydrochloric acid and in ethanol enabled Linderstranl-Lang and Kodama 1101 to characterize seven fractions in casein. These observations were confirmed by CherbuIiez and Schneider 1111 by fractional salting out, and later by
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