Casein

Casein, the most important protein substance of milk, belongs to the group of nucleoalbumins (contains about 0.5-0.8% phosphorus), is a weak acid and approaches the properties of alkaline albuminates. C. is a specific product of secretion of the mammary gland, in which it is synthesized, and in nature has been found with certainty only in milk. C. is a white powder, insoluble in water, soluble in alkalis with the formation of salts (caseinates). Solutions of C. salts do not coagulate upon boiling, rotate the plane of polarization of light to the left. From solutions of its salts, C. is precipitated by acids, in excess of which it dissolves again. In milk, C. is present in the form of calcium salts. C. differs from most other proteins in that it completely lacks glycine and a carbohydrate group. Casein is relatively rich in tryptophan and tyrosine. Composition of C. Glycine ..... Alanine ...... Leucin.....ok. Valine ....... Glutamic acid Asparagine. acid Serine ....... Cystine...... (of cow's milk in %). 0.0 Lysine...... 1.5 Arginine..... 10

Phenylalanine . . 7

Glucosamine . . , 7.6 3.8 3.5 4.5 6.7 2.2 2.6 0.0 C. of milk of different animals somewhat differ in their composition and properties. When milk sours (or when acid is added), a precipitate of C. is formed, capturing part of the milk fat (cottage cheese). Different from this process is the coagulation of milk by rennet (chymosin), which consists in the formation from C. of paracasein, which with the calcium salts of milk forms an insoluble compound - cheese (see Milk). (English authors call the milk C. caseinogen, and the precipitate of paracasein - casein).-Quantitative determination of C. in milk is based on determining the N content in the C. precipitate, obtained by acidifying milk with acetic acid. Human milk contains 1.4%, cow's milk - 4.8% C.; various cheeses contain from 20% to 40% paracasein. When chymosin acts on human milk, paracasein precipitates in the form of finer and more easily digestible flakes than paracasein of cow's milk.-Being almost the only protein in the diet of a breast-fed infant (along with albumin and globulin of milk), C. plays an extremely important role in the nutrition of the child. From this point of view, it is especially important that C. is a complete protein in terms of the amino acids contained in it (the glycine missing in it is easily synthesized in the body) and is well digestible; it is easily broken down by both pepsin and trypsin, passing through the stage of albumoses (caseoses). These same properties make C. (in the form of milk and cheese) a valuable food product in general and in particular a dietary product in various diseases of the digestive system. Heat of combustion of 1 g of C. equals 5.86 cal. Since C. can be obtained in a very pure form, it is a favorite protein for preparing artificial nutrient mixtures used in the experimental study of problems of nutritional physiology. Solutions of C. are also used for diagnostic purposes to detect trypsin (resp. digesting ability) in duodenal contents or in feces (see Gross-Fuld method). Casein is also used in technology as a material for making plastic mass - galalite.

A. Braunshtein. To obtain C., skimmed milk is diluted with 4 volumes of water and precipitated with 0.1-1% acetic acid. The precipitated C. is dissolved in a weak alkali, again precipitated with acetic acid, filtered, washed with water, then with alcohol and ether, and dried.-In dermatology, C. is used to prepare Unna's casein ointment, which is a good base for various medicinal preparations, as it forms a thin, dry, elastic coating on the skin. Unna's ointment contains dry C. 14.0, caustic alkali 0.43, glycerin 7.0, vaseline 21.0, boric acid 1.0, water 56.57.-Preparations of C. 1. Nutrose, Nutrose, Sodium caseinate-sodium salt of C. of acidic reaction. White powder, easily soluble in water. Nutrose contains 65% protein, 4% mineral substances and 20% nitrogen-free substances. Used as a nutrient. 10.0 of nutrose corresponds in protein content to 0.5 l of milk.-2. Plasmon-milk protein of Siebold; obtained by mixing freshly prepared C. with sodium bicarbonate. Soluble in hot water, odorless, and has a milk taste. Used as a nutrient for febrile and gastric patients. Plasmon reduces the excretion of uric acid, therefore it is indicated in gouty diathesis,-3. Larosan, Casein-calcium; contains 2.5% calcium oxide. White powder, soluble in water; the solution has a neutral reaction. Used in pediatric practice to replace protein milk, for which 20g of larosan is dissolved in 0.5 l of water and 0.5 l of milk.-4. Caseosan, Caseosan, 4.5% sterile solution of C., used in protein therapy. Dose: intramuscularly 0.5 - 3 and up to 5 cm³ per injection. Caseosan is used for "Reiztherapie" in a mixture with turpentine (Caseoterpol), in combination with iatren-iatrencasein.

I. Zelikin.