[A comparative study of the biological value of qualitatively different proteins and their susceptibility to attack by digestive proteinases].

It has been established that according to the principal criteria, namely the attackability by alimentary proteinases and biological value (potential and experimental), casein and fibrinogen are closely related proteins. Attackability of experimental casein (cleaned from glycomacropeptide) by alimentary proteinases rises after the action of denaturating agents. This fact brings together casein and globular proteins.

[Heterogeneity and physiological activity of bovine k-casein proteolysis products].

Gel chromatography in columns with Sephadex G-50 and biogel P-2 was used to separate a number of fractions formed in k-casein of cow's milk after short-term treatment with swine trypsin. These fractions, similar to beta-casomorphin, are capable of reducing the respiration and heart rates in rabbits after intravenous injection in a dose of 100 micrograms/kg, that suggests their capacity for interaction with opiate receptors. Some fractions injected subcutaneously induce in starving animals an electroencephalographic picture of satiation, similar to that observed after cholecystokinin injections.

[A peptide bioregulator from bovine kappa-casein].

A number of peptides were isolated from pepsin hydrolyzate of cow k-casein by means of gel filtration on Sephadex G-50 and Biogel P-2, Dowex WX2 ion exchange chromatography in the pH step-wise gradient and dialysis using Sephadex G-10. The peptide material, after intravenous administration at a dose of 20 micrograms/kg of body mass, developed on electroencephalograms of various brain structures of starved rabbits the high amplitude, high frequent oscillations of electric potential corresponding to the effect of food satiation or to the action of cholecystokinin. Analysis of amino acid composition showed that the peptide fraction appears to be a fragment of para-k-casein moiety localized near one of Tyr residues containing in the protein molecule.

[Isolation, amino acid composition and type of action of gastric secretion inhibitors derived from k-casein].

Yield of an inhibitor of gastric secretion and its activity were increased after additional step of the k-casein purification as well as a result of increase in the enzyme/substrate ratio at the step of enzymatic hydrolysis and of substitution of the filtrate dialysis by extraction with ether. Amino acid analysis of the gel chromatographic fractions of inhibitor demonstrated the presence of para-k-casein fragments in its molecule. As shown by kinetics of inhibitory action the preparation included two inhibitors of gastric secretion.