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At least 19 recordsLinked to original sources
PubMed1978

The monomeric casein composition of different size bovine casein micelles.

The fractionation by size of casein micelles from bovine skim milk was performed by chromatography on controlled-pore glass granules (CPG-10/3000). Acid precipitation of the fractionated proteins in combination with polyacrylamide gel electrophoresis gave no indication for monomeric caseins in the whey fractions. A factor besides low temperature appears necessary for the dissociation of, for example, beta-casein from casein micelles. The casein composition was studied by DEAE-cellulose chromatography. In bulk skim milk the alphas-, beta- and kappa-caseins were shown to occur in the following relative amounts: 52, 33 and 15%, respectively. The distribution varies with the size of the micelle. In large and medium size micelles the alphas1-casein content is almost constant; beta-casein and kappa-casein appear to be complementary so that the kappa-casein content increases with the decrease in the size of the micelle. In small micelles the relative beta-casein content is about 50%, alphas1-casein is only about 33%. We suggest that beta-casein plays a special role as initiator of micelle formation, and that alphas1-casein stabilizes the structure of the larger micelles.

Animals↗
PubMed1979

Phosphorylation of casein by human erythrocyte membrane-bound protein kinase: competition of casein with endogenous substrates.

The possibility that spectrin and band-3 protein are phosphorylated by the same membrane-bound protein kinase was investigated by adding casein to unsealed erythrocyte ghosts and examing competition of the three proteins for phosphorylation. The extent of spectrin and band-3 protein phosphorylation was reduced by up to approximately 55%. This indicated that casein was competing with these endogenous substrates for phosphorylation and was most probably phosphorylated by the same protein kinase(s). Furthermore, the extent of inhibition of the phosphorylation of the two endogenous substrates was indistinguishable over the range of casein concentrations tested (0.1 to 5 mg/ml). This indicates that spectrin and band-3 protein may be phosphorylated by the same protein kinase. In contrast, casein was found to have no effect on the cAMP-dependent phosphorylation of band 4.5. This result indicates that casein only competes with the endogenous proteins phosphorylated by the cAMP-independent protein kinase(s). The extent of reduction of endogenous substrate phosphorylation in the presence of casein was found to be constant over incubation periods of 1 to 15 min, indicating that this reduction was not due to consumption of ATP. Since the spectrin and band-3 protein phosphorylations were specifically and identically reduced by casein and these reductions were not due to the ATP consumption or to a general alteration of the membrane, we conclude that the two substrates are likely phosphorylated by one kinase which also phosphorylates casein.

Caseins↗
PubMed1979

Effect of voluntary exercise on physiological function and feeding behavior of mice on a 20% casein diet or a 10% casein diet.

The effects of voluntary exercise on growth and food intake, body composition, organ weight, and fatty acid composition of adipose tissue of mice fed on a 20% casein diet or a 10% casein diet were examined. The weight gain was greater for the 20% casein nonexercise group (20% NE) than that for the 20% casein exercise group (20% E), 10% casein exercise group (10% E) and 10% casein nonexercise group (10% NE). There were no significant differences between the groups except the 20% NE. In 20% E and 10% E, body fats decreased markedly. On the other hand, a very high ratio of protein was present in the body composition of both groups. In the 20% and 10% casein diet groups, food intake was increased by voluntary exercise, but there was no significant difference between 10%E and 10% NE except occasional periods during these experiments. After 6 weeks of age, 10% E had a tendency to undertake more voluntary exercise than 20% E, though the difference was not statistically significant. Development of the heart and gastrocnemius muscles was accelerated by voluntary exercise and epididymal fat tissue was markedly decreased.

Adipose Tissue↗
PubMed1977

Bovine alpha s0 casein; a phosphorylated homologue of alpha s1 casein.

After consideration of its electrophoretic behaviour, amino acid composition and phosphate content, bovine alpha s0 casein has been shown to differ from alpha s1 casein only in respect of its phosphate content. The presence in alpha s0 casein of one phosphate residue more than occurs in alpha s1 casein was confirmed by comparative degradative studies performed on both proteins. From these it was concluded that alpha s0 casein may be considered as being alpha s1 casein which has been modified by phosphorylation of the seryl residue located at position 41.

Amino Acid Sequence↗
PubMed1975

Comparative micelle structure. IV. The similarity between caprine alphas-casein and bovine alphas-3- casein.

The major component of caprine (goat) alphas-casein has been isolated by DEAE-and CM-cellulose chromatography in buffers containing urea and 2-mercaptoethanol. The protein has a molecular weight of 25700 as determined by gel filtration on Sepharose 6B in guanidine hydrochloride. Its composition, Asp17, Thr14, Ser14, Glu45, Pro18, Gly4, Ala10, Cys2, Val12, Met4, Ile12, Leu12, Tyr11, Phe8, His5, Lys22, Arg6, Trp2 and 7 phosphate residues, is much closer to that of bovine alphas3-casein than to bovine alphas1-casein. The caprin alphas-casein is more easily precipitated with Ca2+ than bovine alphas3-casein at 37 degrees C, pH 6.8, which in turn is more easily precipitated than bovine alphas1-casein.

Amino Acids↗
PubMed1977

[Primary structure of the casein macropeptide of kappa casein of buffalo].

The complete amino acid sequence of Italian water buffalo (Bubalus arnee) caseinomacropeptide, the C-terminal fragment released from kappa-casein by chymosin, has been determined. It contains 64 amino acid residues including one phosphoserine and differs from its bovine (Bos taurus) B counterpart by 10 amino acid substitutions. The sequence of the last 11 amino acid residues of para-kappa-casein is also reported. In relation to the Ala148/Asp substitution which is responsible for the different electrophoretic behaviour of bovine kappa-caseins B and A, water buffalo kappa-casein is homologous to the bovine variant B. It is suggested that a variant Thr136-Ala148 might be the wild type of the Bos genus.

Amino Acid Sequence↗
PubMed1977

Further characterization of rennin action on kappa-casein using carboxymethylcellulose: effects of various additives on the enzymatic hydrolysis of kappa-casein.

The effects of various additives on the reaction of rennin with kappa-casein were investigated by using carboxymethylcellulose. Both urea and sodium 1-anilino-8-naphthalenesulfonate effectively inhibited rennin action at concentrations larger than 2 M and 2 mM, respectively. These reagents, however, activated the enzyme action at the lower concentrations. Both alpha S-and beta-caseins had some ranges of concentrations in which the rennin reaction was activated. Calcium chloride had an inhibitory effect on the rennin action. Neither mercaptoethanol nor KCl had any appreciable effect on the enzymatic hydrolysis of kappa-casein. These results are analyzed in terms of the association and dissociation of kappa-casein due to the presence of these additives in the reaction solutions.

Adsorption↗
PubMed1979

Hydration of casein micelles: kinetics and isotherms of water sorption of micellar casein isolated from fresh and heat-treated milk.

Water vapour sorption isotherms of casein micelles prepared from raw milk and various heat-treated milks were determined. The equilibrium water contents of the heated preparations were markedly lower than that of the raw-milk casein over the whole range of vapour pressures studied. An analysis of the sorption isotherms in the relative vapour pressure range 0.1--0.45, according to the Brunauer, Emmett & Teller (1938) equation, showed that there were significant differences between preparations in the computed monolayer contents. Differences in the rates of water sorption were also observed between the different preparations. As judged from the amount of absorbed water, the influence of the heating methods could be ranked in the order: HTST (92 degrees C) approximately UHT (direct) less than UHT (indirect) less than HTST (72 degrees C).

Animals↗
PubMed1979

Covalent bonds formed in proteins during milk sterilization: studies on caseins and casein peptides.

Formation of covalent bonds at milk sterilization temperatures was studied using caseins and casein peptides. At 120 degrees C lysinoalanyl residues produced even at pH 7.0 were derived from intra-molecular interactions between phosphoserine and lysine; the conditions of formation were determined. It was also found that the formation fo isopeptidic cross-links was significant with conditions more severe than those used for milk sterilization.

Amino Acids↗
PubMed1979

Novel opioid peptides derived from casein (beta-casomorphins). II. Structure of active components from bovine casein peptone.

Material with opioid activity had been isolated from an enzymatic casein digest. It was shown to contain a pure heptapeptide with the sequence Tyr-Pro-Phe-Pro-Gly-Pro-Ile. The identity between the opioid principle and the peptide was proven by the fact that chemical reagents or enzymes effecting one would effect the other. After carboxypeptidase Y digestion a pentapeptide, Tyr-Pro-Phe-Pro-Gly, could be isolated; this peptide showed a higher opioid activity than the heptapeptide. The opioid peptides were highly resistant towards proteolysis, even by pronase. The sequence of the hepatapeptide identified it as a fragment of bovine beta-casein. Therefore it was named beta-casomorphin.

Amino Acid Sequence↗
PubMed1979

Novel opioid peptides derived from casein (beta-casomorphins). I. Isolation from bovine casein peptone.

A material which displayed opioid activity in the guinea pig ileum longitudinal muscle-myenteric plexus preparation was extracted from an enzymatic casein digest into chloroform/methanol. The extract was roughly purified by adsorption/desorption procedures using charcoal and Amberlite XAD-2 resin as adsorbents. A high degree of purity was achieved by high-pressure liquid chromatography of the material on muBondapak C18 and mu-Porasil columns and finally by gel filtration chromatography on a Bio-Gel P-2 column. Several pronase-resistant compounds with opioid activity were obtained.

Animals↗
PubMed1979

Casein turnover in rabbit mammary explants in organ culture.

1. Explants of mammary gland from mid-pregnant rabbits were cultured in medium 199 containing insulin, prolactin and cortisol, and specific anti-casein immunoglobulin G was used to measure the amount, rate of synthesis and rate of degradation of casein in the explants in the presence of hormones and after removal of hormones from previously stimulated tissue. 2. The amount of casein in particle-free supernatants prepared from mammary explants was measured by ;rocket' immunoelectrophoresis. 3. The rate of incorporation of l-[4,5-(3)H]leucine into casein was measured after isolation of the casein by immunoadsorbent chromatography and polyacrylamide-gel electrophoresis in the presence of urea and sodium dodecyl sulphate. 4. Casein accumulates in mammary explants in the presence of insulin, prolactin and cortisol, but not in the absence of hormones. Removal of hormones after 24h in culture results in a decrease in the rate of accumulation of casein in the explants. 5. Casein-synthetic rate increases in mammary explants in the presence of insulin, prolactin and cortisol, but not in the absence of hormones. Removal of hormones after 24h in culture results in continued casein synthesis at approx. 30% of the rate in the presence of hormones. The synthetic rate does not decrease to values observed in explants cultured throughout in the absence of hormones. 6. Casein is not degraded in mammary explants during a phase of rapid casein accumulation (36-72h) in the presence of hormones. Furthermore casein is not degraded when hormones are removed from the tissue after between 36 and 72h in culture. 7. Casein is glycosylated in mammary explants; the extent of glycosylation parallels the rate of synthesis. The glycosylated protein is rapidly secreted from the tissue. 8. The results are consistent with the notion that after hormonal stimulation mammary explants from mid-pregnant rabbits synthesize, glycosylate and rapidly secrete casein. Removal of hormones decreases the synthetic rate of casein, but does not cause the accumulation of a pool of degradable casein in the lobuloalveolar cells.

Animals↗
PubMed1979

Responses to post-ruminal infusions of casein and arginine, and to dietary protein supplements in lactating goats.

1. In Expt 1 a study was made in goats of responses in terms of milk production, nitrogen utilization and plasma amino acids to abomasas infusions of casein (45 g/d) in goats given 2.5 kg/d of a ration containing crude protein (N x 6.25) at 109 (L1) or 146 (H1) g/kg. 2. In Expt 2 a study was made in goats of responses in terms of milk production, nitrogen utilization, plasma amino acids and growth hormone levels to abomasal infusions of casein (45 g/d) or arginine (25 g/d) in goats given 2.3 kg/d of a ration containing crude protein (N x 6.25) at 104 g/kg (L2). These observations were made also in goats given a ration containing crude protein at 136 g/kg (H2). 3. Milk production in Expt 1 was 2.75, 2.45 and 2.76 kg/d on L1+casein, H1 and H1+casein treatments respectively, the response to casein infusion being significant (P less than 0.05). Milk production in Expt 2 was 1.90, 2.04, 1.96 and 1.96 kg/d on L1, L2+casein, L2+arginine and H2 treatments respectively, and the differences were not significant. 4. Total N intake in Expt 1 was 49, 58 and 64 g/d on L1+casein, H1 and H1+casein treatments respectively. Faecal N was similar on the three treatments (14 g/d), urinary N was 15, 23 and 30 g/d and milk N was 14, 12 and 14 g/d on the respective treatments. Total N intake in Expt 2 was 33, 40, 43 and 44 g/d on L2, L2+casein, L2+arginine and H2 treatments respectively. Faecal N was similar on the four treatments (12 g/d), urinary N was 7, 10, 13 and 14 g/d and milk N was 9, 9, 8 and 8 g/d on the respective treatments. 5. The concentration of indispensable amino acids in plasma was increased by casein infusion in both experiments. It was 1279, 825 and 1133 micrometers/l on L1+casein, H1 and H1+casein treatments respectively in Expt 1, and 1081, 1582, 1055 and 1163 micrometers/l on L2, L2+casein, L2+arginine and H2 treatments respectively in Expt 2. 6. The concentration of arginine in plasma was doubled 1 h after the onset of arginine infusion in Expt 2, Growth hormone levels in plasma were not increased when arginine levels rose following arginine infusion. and did not differ between treatments. 7. The results of the two experiments showed that the stimulatory effect on milk production of intra-abomasal infusion of casein was not reproduced by increasing the dietary intake of protein or by infusing arginine. The results of the second experiment showed that abomasal infusion of arginine did not stimulate production of growth hormone and that growth hormone apparently was not implicated in the effects of casein infusion on milk production.

Abomasum↗
PubMed1979

The primary structure of the ovine beta-caseins.

Ovine whole casein contains 2 multiphosphorylated beta-casein components designated as beta 1 and beta 2-caseins. The complete sequence of beta 1-casein and the partial sequence of beta 2-casein have been determined from cyanogen bromide and tryptic digests. The ovine beta 1 and beta 2-caseins have the same polypeptide chain and appear to differ only in that they contain 6 and 5 phosphates respectively. The amino acid composition of ovine beta 1-casein can be written as: Asp4, Asn4, Thr10, ThrP1, Ser9, SerP5, Glu19, Gn21, Pro34, Gly5, Ala4, Val21, Met6, Ile9, Leu22, Tyr3, Phe9, Trp1, Lys12, His5, Arg3. Compared to bovine beta-casein A2, which is made up of 209 residues, ovine beta 1-casein has a deletion of 2 residues (either Pro-179--Tyr-180 or Tyr-180--Pro-181) and 20 largely conservative amino acid substitutions. Although 20% of the substitutions involve proline residues, the proline contents of ovine beta 1 and bovine beta A2-caseins are very similar, around 16%. The average hydrophobicity, calculated according to Bigelow, is 5.51 kJ/residue, which is similar to that calculated for bovine beta-casein A2. The cluster of 4 phosphorylated serine residues and the highly charged nature of the amino terminal region observed for bovine beta-casein are conserved in the ovine beta-caseins. The substitution from Ile-12 (bovine) to Thr-12 (ovine) results in a new phosphorylation site, according to the phosphorylation code proposed for caseins. This site is only partially phosphorylated hence the occurrence of both beta 1 and beta 2-caseins in ovine milk.

Amino Acid Sequence↗
PubMed1979

Role of mammary casein kinase in the phosphorylation of milk proteins.

Casein kinase from lactating bovine mammary gland catalyses the transfer of the terminal phosphoryl group of ATP to specific serine residues in dephosphorylated caseins. Best substrates for casein kinase are the dephosphorylated proteins (bovine alpha S1- and beta-caseins and pepsin), unphosphorylated human beta-casein and the dephosphorylated peptide (residues 1-25) from bovine beta-casein. Results obtained with bovine and human beta-caseins indicate that the two serines underlined in the cluster Ser-Leu-Ser-Ser-Ser are particularly susceptible to the action of casein kinase. Since a similar sequence is found in dephosphorylated alpha S1-casein, it is probable that serines in this region of alpha S1-casein are also phosphorylated. The results support the concept that certain serines in casein are particularly susceptible to phosphorylation by casein kinase.

Amino Acid Sequence↗