Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “CASEIN”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 433 records · Page 24Linked to original sources
PubMed1990

Nutritional characteristics of a neoglycoprotein, casein modified covalently by glucose.

Glucose was combined covalently with the epsilon-amino groups of lysyl residues of bovine casein in the presence of sodium cyanoborohydride as a reducing reagent by reductive alkylation, forming stable secondary amine linkages. Solubility characteristics and nutritional values of the neoglycoprotein were examined. The degree of modification (%) of the glucosylated casein was 82.5. Solubility of the modified casein was increased by the attachment of glucose. The modification did not disturb the digestion of casein by pepsin or trypsin. Rat feeding experiments using 10% protein diets demonstrated that the protein efficiency ratio (PER) of the modified casein was 0.35 +/- 0.33 compared with 2.99 +/- 0.29 for the unmodified casein. When the modified casein was supplemented with L-lysine to equal the level of total lysine of unmodified casein, the PER value was increased to 2.21 +/- 0.29. Nitrogen balance experiments showed that the modified casein was digested completely. On the other hand, biological value and net protein utilization of the modified protein were shown to be considerably lower than those of the unmodified casein.

Journal Article↗
PubMed1998

Influence of Protein Interfacial Composition on Salt Stability of Mixed Casein Emulsions.

The influence of casein surface composition on the stability toward flocculation by sodium chloride has been investigated for oil-in-water emulsions (20 vol % oil, 1 wt % total protein) prepared with a mixture of alpha(s1)-casein + beta-casein. It has been observed that the poor salt stability of emulsions containing 100% alpha(s1)-casein is greatly enhanced by the replacement of about one-third of the alpha(s1)-casein by beta-casein. With around half of the adsorbed protein layer consisting of beta-casein, emulsions remain stable at ionic strengths of 2 M NaCl in the presence or absence of calcium ions (5 mM). At the point of droplet flocculation in these emulsions, most of the casein present is associated with the surface of the droplets. These results provide definitive evidence for the important influence of the compositional balance in sodium caseinate on the colloidal stability behavior of casein-based emulsions.

Journal Article↗
PubMed1984

Casein kinase activity in rat mammary gland Golgi vesicles. Demonstration of latency and requirement for a transmembrane ATP carrier.

A Golgi vesicle-enriched preparation from mammary tissue of lactating rats has been used to investigate the phosphorylation of caseins in vitro. Casein kinase, together with its casein substrates, is enclosed within the lumen of Golgi membrane vesicles and has a requirement for Ca2+ and ATP. The permeability characteristics of the Golgi membrane to ATP and Ca2+ therefore have a possible regulatory influence on casein kinase activity. This influence has been investigated by alteration of the permeability characteristics by using several agents having differing degrees of selectivity. The ionophore A23187, which permits loss of Ca2+ from the vesicles, caused a decrease in casein phosphorylation which could be reversed by externally supplied Ca2+. Alamethicin, an ionophore that creates larger transmembrane channels, caused an increase in casein phosphorylation. This increase showed a requirement for divalent metal ions which could be satisfied by either Ca2+ or Mn2+. Under the same conditions, La3+ was inhibitory. Triton X-100 caused loss of intravesicular Ca2+, yet this was accompanied by an increase in phosphate incorporation into the caseins. We conclude from these results that the binding site on casein kinase for ATP is within the Golgi membrane barrier and that they imply the presence of a transmembrane ATP-transport mechanism. Inhibition of casein phosphorylation by atractyloside and carboxyatractyloside lends support to this concept.

Alamethicin↗
PubMed1997

Rat liver Golgi apparatus contains a protein kinase similar to the casein kinase of lactating mammary gland.

By using a beta-casein-derived specific peptide substrate for mammary gland Golgi-enriched-fraction casein kinase, phosphorylating activity has been detected in the Golgi apparatus of rat liver, spleen and to a lesser extent, kidney and brain, while the other post-nuclear cytoplasmic fractions are totally devoid of such a casein kinase activity. In contrast ubiquitous protein kinases CK1 and CK2 (casein kinases 1 and 2), tested with their specific peptide substrates, display different subcellular distribution and are almost undetectable in the Golgi fraction. The absence of CK2 in the Golgi fraction has been also confirmed using specific antibodies. The relatedness between the liver Golgi apparatus casein kinase (G-CK) and the bona fide mammary gland Golgi-enriched-fraction casein kinase (GEF-CK) is supported by a variety of observations, notably: (a) identical peptide substrate specificity, consistent with an S-X-E-X consensus sequence; (b) preference for Mn2+, and, to a lesser extent, Co2+, over Mg2+, as activating cation; (c) superimposable elution profiles from DEAE-Sepharose, heparin-Sepharose, and Superdex 200, this latter consistent with a molecular mass around 500 kDa; (d) insensitivity to staurosporine and heparin (a potent inhibitor of CK2) and inability to use GTP as phosphate donor (by contrast to CK2). These data provide the evidence for the existence of a third class of ubiquitous casein kinases here termed G-CK, distinct from CK1 and CK2, specifically located to the Golgi apparatus and related to the bona fide casein kinase(s) responsible for the phosphorylation of casein secreted from lactating mammary gland. The possible involvement of G-CK in the phosphorylation of secretory pathways proteins at S-X-E motifs is discussed.

Amino Acid Sequence↗
PubMedDate not supplied

Bovine beta-casein antibodies in breast- and bottle-fed infants: their relevance in Type 1 diabetes.

BACKGROUND: Bovine beta-casein is a cow's milk protein that targets both humoral and cellular immune responses in patients with Type 1 diabetes and, to a lesser degree, also in normal subjects. In this study we aimed to determine whether the avoidance of cow's milk consumption early in life could prevent the development of antibody response to bovine beta-casein despite the mother being exposed on a daily basis to cow's milk consumption. MATERIALS AND METHODS: We measured the antibody response to bovine beta-casein using an ELISA method in 28 healthy infants under 4 months of age, of whom 16 were exclusively breast-fed and 12 were bottle-fed with cow's milk. In addition, beta-casein antibodies were measured in 37 prepubertal children with Type 1 diabetes and in 31 healthy children who were exposed to cow's milk or dairy products to see whether differences in antibody titers exist in this young age group. Antibodies binding to beta-casein were also evaluated by immunoblotting analysis. RESULTS: Elevated levels of beta-casein antibodies were found in bottle-fed infants compared to breast-fed infants (p<0.0001). Antibody levels to bovine beta-casein were also significantly higher in children with Type 1 diabetes compared to age-matched controls (p=0.03). By western blot analysis we confirmed specific binding to bovine beta-casein in bottle-fed infants, in children with Type 1 diabetes and in controls exposed to cow's milk, but not in infants who were exclusively breast-fed. CONCLUSIONS: The results of this study indicate that breastfeeding within the first 4 months of life prevents the generation of antibody response to bovine beta-casein despite the mothers' consumption of cow's milk during the breastfeeding period. These findings may have relevance for disease prevention.

Animals↗
PubMed2002

Identification of caseins in goat milk.

The importance of goat milk in infant diet is growing, because it is reported that goat's milk in some cases is less allergenic than cow's milk. This is due probably to the lower presence of caseins associated with a specific type of alpha(s1)-casein. In caprine breeds, four types of alpha(s1)-casein alleles are identified and associated with various amounts of this protein in milk. The contribution of strong alleles to the goat milk is approximately 3.6 g/L of alpha(s1)-casein, while for middle alleles is only 1.6 g/L, weak alleles 0.6 g/L. The contribution of null allele is very low (or non-existent). The quantity of total caseins in caprine milk is positively correlated with the amount of alpha(s1)-casein. Milk from animals possessing strong alleles contain significantly more total caseins than milk from animals without those alleles. This is important because animals with mild alleles can be employed to produce milk for allergic subjects while the other animals can be used to produce milk for the dairy industry. This work shows casein profiles of two types of classified goat milk (B, strong alpha(s1) allele, 0, null alpha(s1) allele) with two-dimensional electrophoresis coupled with matrix-assisted laser desorption/ionization-time of flight mass spectrometry, and it confirms the different polymorphisms at locus alpha(s1) casein.

Alleles↗
PubMed1993

Transport of casein submicelles and formation of secretion granules in the Golgi apparatus of epithelial cells of the lactating mammary gland of the rat.

Lactating mammary glands fixed by perfusion with 5% glutaraldehyde subsequently were postfixed with potassium ferrocyanide reduced osmium or were treated with tannic acid. Stained thin sections were examined with the electron microscope and stereopairs were prepared. The distribution of casein submicelles was analyzed in the various components of the Golgi apparatus. The Golgi stacks were composed of five or six elements, all of which contained casein submicelles 20 nm in diameter. The cis-tubular network or cis-element, as well as the underlying three or four midsaccules, showed these casein submicelles either attached to their membrane or free in the lumen. The trans-most element of the stacks formed distended prosecretory granules in which both isolated or clustered casein submicelles were suspended in an electron-lucent fluid. These micellar aggregates increased in size and became progressively more compact to form spherical dense bodies or casein micelles, in which the individual 20 nm particles could easily be resolved. Casein micelles were seen in secretory granules in addition to a wispy material of low density. The numerous small spherical vesicles (80 nm or larger) seen on the cis, lateral, or trans aspects of the stacks did not appear to contain free casein submicelles. This raises questions regarding the role of these vesicles in the transport of casein macromolecules through the Golgi stacks. It was noticeable that in this Golgi apparatus a trans-Golgi network was limited to a few small residual tubules free from casein submicelles. It thus appears that the greater part of the trans-most Golgi element gives rise to the large prosecretory granules. After leaving the Golgi region and prior to exocytosis, the secretory granules often fuse to form larger granules before exocytosis.

Animals↗
PubMed1987

Proteolytic activity of lactic acid bacteria in skim milk with special reference to the biodegradation of casein fractions.

Streptococci and lactobacilli were assayed for their proteolytic activity in pasteurised (95 degrees C for 30 min) fresh Friesian cows' skim milk incubated at 30 degrees C for 48 h. Lactobacilli were more proteolytic than the streptococci except S. faecalis subsp. liquefaciens. S. faecalis and S. thermophilus followed S. lactis subsp. diacetylactis in the proteolytic activity. Electrophoretic analysis of the precipitated casein revealed K-, pre-beta- and the small slow band of alpha s1-casein to be the most fractions and beta-casein the least fraction susceptible to the biodegradation. S. faecalis subsp. liquefaciens was the only organism able to degrade beta-casein to 3 fractions within 48 h. S. lactis with its subsp. diacetylactis was characterized by its inability to degrade gamma-casein. Addition of 2.0 g glucose, 0.5 g yeast extract, 2.0 mmol Mg2+, 0.5 mmol Mn2+ and 0.1 mmol Fe2+/l of skim milk culture of each L. casei and L. plantarum increased acid formation but decreased proteolysis. 6% NaCl was inhibitory to both. After 60 days at 18 degrees C, a fraction, probably derived from beta-casein, was noticeable. The large intense band of alpha s1-casein appears to be degraded gradually to only small peptides which in turn are transferred immediately into the cells. The hydrolysis of gamma-casein and beta-casein also appears to be inhibited by exogenously supplied NaCl and nutrients, respectively.

Animals↗
PubMed2005

Magnetic dye affinity beads for the adsorption of beta-casein.

Casein is well known as a good protein emulsifier and beta-casein is the major component of casein and commercial sodium caseinate. Dye affinity adsorption is increasingly used for protein separation. beta-Casein adsorption onto Reactive Red 120 attached magnetic poly(2-hydroxyethyl methacrylate) (m-PHEMA) beads was investigated in this work. m-PHEMA beads (80-120 microm in diameter) were produced by dispersion polymerization. The dichlorotriazine dye Reactive Red 120 was attached covalently as a ligand. The dye attached beads, having a swelling ratio of 55% (w/w) and carrying different amounts of Reactive Red 120 (9.2 micromol . g(-1)-39.8 micromol . g(-1)), were used in beta-casein adsorption studies. The effects of the initial concentration, pH, ionic strength and temperature on the adsorption efficiency of dye attached beads were studied in a batch reactor. The non-specific adsorption on the m-PHEMA beads was 1.4 mg . g(-1). Reactive Red 120 attachment significantly increased the beta-casein adsorption up to 37.3 mg . g(-1). More than 95.4% of the adsorbed beta-casein was desorbed in 1 h in a desorption medium containing 1.0 M KSCN at pH 8.0. We concluded that Reactive Red 120 attached m-PHEMA beads can be applied for beta-casein adsorption without significant losses in the adsorption capacities.

Caseins↗
PubMed1994

Quantitative characterization of bovine plasminogen binding to caseins.

The binding of bovine plasminogen to whole casein, alpha s-casein, beta-casein, and kappa-casein is responsible for the progressive proteolysis of milk and dairy products. A sensitive and accurate microparticle-enhanced nephelometric immunoassay was developed to measure free plasminogen after interaction between bovine plasminogen and caseins and the quantitative parameters of plasminogen/casein binding were established. Two classes of binding sites for plasminogen were found in this study on each of the investigated caseins. Their dissociation constants (Kd) were determined by varying the plasminogen concentration at pH 6.6 and performing Scatchard analysis. The two binding sites appeared to be one of high affinity (Kd = 32 nM) and the other of lower affinity (Kd > 370 nM). The number of both binding sites per casein monomer was low (0.04 to 0.53). The great propensity of casein monomers to self-associate in homopolymers where plasminogen binding sites could be hidden and in copolymers present in bovine milk in the form of whole casein micelles accounts for calculated binding sites < 1 per monomer.

Animals↗
PubMed1994

The effect of milk and casein proteins on the adherence of Streptococcus mutans to saliva-coated hydroxyapatite.

Experiments sought to determine the nature of the binding of milk proteins to hydroxyapatite (HA) and to saliva-coated hydroxyapatite (sHA), and to determine the effect of milk and casein on the adherence of Streptococcus mutans GS-5 to sHA. The binding of radiolabelled alpha-casein to HA was reduced when incubated simultaneously with parotid saliva, and enhanced in the presence of milk. The binding of beta- and kappa-casein to HA was unaffected by the presence of parotid saliva and enhanced by the presence of milk. The in vitro bacterial adherence of Strep. mutans GS-5 to sHA beads was reduced when beads were coated with milk instead of buffer, or when bacteria were added to sHA in the presence of milk instead of buffer. Casein proteins (alpha, beta, kappa) added to sHA simultaneously with bacteria inhibited the adherence of Strep. mutans GS-5 to sHA. kappa-Casein, when bound to sHA, inhibited streptococcal adherence to sHA; alpha- and beta-casein, when bound to sHA, had no effect on streptococcal adherence. Fractionation of kappa-casein by anion-exchange chromatography revealed the anti-adherence activity of kappa-casein was mediated primarily by a 40,000 mol. wt. glycoprotein-containing fraction. These data show that milk, particularly kappa-casein fractions, can modulate the adherence of Strep. mutans GS-5 to SHA surfaces in vitro.

Adult↗
PubMed1975

Multiple forms of casein kinase from rabbit erythrocytes.

Two rabbit erythrocyte casein kinases, GTP:casein kinase I and GTP:casein kinase II, have been purified 29 000- and 47 000-fold, respectively. Studies employing sucrose density gradient centrifugation indicate that kinase I has a molecular weight of about 9.5 - 10(5) (25 S) and kinase II about 1.4 - 10(6) (32 S). These enzymes can utilize either ATP or GTP as the phosphoryl donor. Among various protein substrates examined, these kinases catalyze the phosphorylation of casein greater than 50% dephosphorylated phosvitin congruent to 50% dephosphorylated casein greater than phosvitin. Histones, protamine and bovine serum albumin are poor phosphoryl acceptors. Kinetic data indicate that both enzymes are inhibited by high casein substrate concentrations which may be partially relieved by NaCl. Both phosphotransferases require Mg(2+) for activity and are optimally active at pH 9.0. The enzymes have apparent Km values of 2.5 - 10(-5) M for GTP, 2 - 10(-5) M for ATP, and 0.4--0.6 mg/ml for casein. The incorporation of the terminal phosphate of GTP into casein as catalyzed by these enzymes is inhibited to varying degrees by ATP, ITP, ADP, and GDP but not by UTP, CTP, GMP, adenosine 3':5'-cyclic monophosphate, and guanosine 3':5'-cyclic monophosphate. In addition, NaF and 2,3-diphosphoglyceric acid are also found to inhibit the activity of both kinases. The effect of 2,3-diphosphoglycerate is interesting and suggests that this metabolite may regulate the activity of the casein kinases in the red blood cells.

Animals↗
PubMed1989

Two physiological substrate-specific casein kinases are present in the bovine mammary gland.

Two species of casein kinase from lactating bovine mammary gland have been identified; a Ca2+- and CM-independent casein kinase and a Ca2+- and CM-dependent casein kinase. The Ca2+- and CM-independent casein kinase phosphorylates previously dephosphorylated alpha s1-, beta- or kappa-casein while the Ca2+- and CM-dependent casein kinase prefers previously dephosphorylated beta- or kappa-casein as substrates. Two activities are indicated by their substrate specificity, sensitivity to Ca2+ and CM, pH maxima, and differential solubilization by anionic detergents. The presence of a regulated casein kinase in the lactating mammary gland suggests that casein phosphorylation may be a regulator of micelle formation or secretion.

Animals↗
PubMed1975

An indirect radioimmunoassay for mouse casein using 125I-labeled antigen.

A new indirect radioimmunoassay was developed for detection of casein in mouse milk and in mammary tissue extract. Preincubation of rabbit gamma globulin to mouse milk casein (Ca2+-rennin precipitate) with unlabeled casein, milk, extracts of mammary tissues of late pregnancy and lactation, virtually blocked subsequent binding of 125I-labeled mouse milk casein to the antibody. Preincubation with mouse serum, bovine serum albumin, rennin, extracts of liver or immature mammary tissue had little effect on [125I]casein binding to the antibody. The inability of [125I]casein to bind to the antibody after preincubation with protein samples, which are likely to contain casein, is indicative of a specific antigen-antibody reaction. The assay is capable of detecting 0.2 mug casein, 1 mug milk proteins and 10 mug lactating mammary tissue extract. The application of the assay was also demonstrated using organ culture of the entire mammary gland. The glands treated with the lactogenic hormones, insulin + prolactin + cortisol, showed a saturation level of antibody-antigen reaction, indicating hormonal induction of casein; whereas, no reaction was observed with the non-treated gland.

Animals↗
PubMed1990

Causes of the decrease in fluorescence due to proteolysis of alpha-casein.

Fluorescence decrease in casein solutions induced by proteolytic enzymes is mainly due to cleavage of alpha-casein, and in particular to alpha S1-casein, which is quantitatively the main component of commercial casein. Treatment of alpha-casein with o-iodosobenzoic acid, diminished its intrinsic fluorescence considerably and abolished the decrease in fluorescence induced by proteolytic cleavage. The carboxyterminal Trp at position 199 in alpha S1-casein contributes approximately 30% to the overall effect, while the Trp at position 164 contributes about 70%. Treatment of alpha-casein with cyanogen bromide lowered the initial fluorescence of the preparation, but, in the resulting fragment, trypsin still diminished some of the residual fluorescence. The velocity of decrease in fluorescence correlates with the distance from the Trp in position 164 at which the peptide bond is broken. This effect seems to be rather unique for the caseins, but particularly for alpha S1-casein; this is due to the existence of a Trp that is in the vicinity of hydrophobic amino acids and which upon hydrolysis, becomes exposed to a more hydrophilic environment.

Amino Acid Sequence↗
PubMed1989

Regulation of intracellular casein degradation by secreted milk proteins.

Intracellular degradation of newly synthesised casein was measured by a pulse-chase method in freshly prepared goat mammary explants. After incubation in medium containing L-[5-3H]proline, explants were washed and cultured again in unlabelled medium containing 5 mM proline; at intervals up to 24 h the amount of radiolabel incorporated in casein was measured. Tissue was obtained in week 33 of lactation after goats had been milked incompletely in one gland (the test gland) for 24 weeks; the contra-lateral (control) gland was milked normally. In explants from the control gland, casein was not degraded during or after secretion: L-[5-3H]proline incorporated in casein increased to a maximum value which was maintained through the chase period. For four out of five goats, explants from the test gland showed a decrease in total [3H]casein radiolabel at 0-4 h of the chase, indicating that a proportion of casein was degraded during secretion. Intracellular casein degradation was also observed when control gland explants were cultured in chase medium containing a goat whey fraction known to inhibit casein production and milk secretion (Wilde, C.J. et al., (1987) Biochem. J. 242, 285-288). This suggests that the greater volume of residual milk left by incomplete milking reduced secretory efficiency, rendering casein susceptible to intracellular degradation, and that this occurred through the action of a secreted milk constituent, which acts as a chemical feedback inhibitor of milk secretion.

Animals↗
PubMed2006

Disulphide bonds in casein micelle from milk.

Mammary epithelial cells synthesised and secreted caseins, the major milk proteins in most mammals, as large aggregates called micelles into the alveolar lumen they surround. We investigated the implication of the highly conserved cysteine(s) of kappa-casein in disulphide bond formation in casein micelles from several species. Dimers were found in all milks studied, confirming previous observation in ruminants. More importantly, the study of interchain disulphide bridges in mouse and rat casein micelles revealed that any casein possessing a cysteine is engaged in disulphide bond interchange; these species express four or five cysteine-containing caseins, respectively. We found that the main rodent caseins form both homo- and heterodimers. Additionally, disulphide bond formation among milk proteins was specific since the interaction of the caseins with cysteine-containing whey proteins was not observed in native casein micelles.

Amino Acid Sequence↗
PubMed2004

Stability and rheology of emulsions containing sodium caseinate: combined effects of ionic calcium and alcohol.

We have investigated the combined effect of ionic calcium and ethanol on the visual creaming behavior and rheology of sodium caseinate-stabilized emulsions (4 wt% protein, 30 vol% oil, pH 6.8, mean droplet diameter 0.4 microm). A range of ionic calcium concentrations, expressed as a calcium/caseinate molar ratio R, was adjusted prior to homogenization and varying concentrations of ethanol were added shortly after homogenization. A stability map was produced on the basis of visual creaming behavior over a minimum period of 8 h for different calcium/caseinate/ethanol emulsion compositions. A single narrow stable (noncreaming) region was identified, indicating limited cooperation between calcium ions and ethanol. The shear-thinning behavior of the caseinate-stabilized emulsions is typical of systems undergoing depletion flocculation. Addition of calcium ions and/or ethanol was found to lead to a pronounced reduction in viscosity and the onset of Newtonian flow. The state of aggregation was correlated with emulsion microstructure from confocal laser scanning microscopy. Time-dependent rheology (18 h) with a density-matched oil phase (1-bromohexadecane) revealed that the visually stable emulsions were time-independent low-viscosity fluids. Surface coverage data showed that increasing amounts of caseinate were associated with the oil-water interface with increasing R and ethanol content. A decrease in free calcium ions in the aqueous phase with moderate increases in R and ethanol content was observed, which is consistent with greater calcium-caseinate binding (aggregation). Ostwald ripening occurred at the high-ethanol emulsion compositions that were stable to depletion flocculation. While the coarsening rate was low, this can account for the cream plug formation observed during gravity creaming experiments. The caseinate emulsion with no ionic calcium or ethanol exhibits depletion flocculation from excess nonadsorbed caseinate submicelles. Addition of calcium ions reduces the submicelle number density via specific calcium-binding in the aqueous phase (fewer, larger calcium-caseinate aggregates) and at the droplet surface (increased surface coverage). Nonspecific ethanol-induced (calcium-dependent) caseinate submicelle aggregation in the bulk phase and on the droplet surface (increased surface coverage) culminates in a reduction in the number density of caseinate submicelles. A narrow window of inhibition of depletion flocculation occurs in systems containing both calcium ions and ethanol, both species combining to aggregate the protein and so reduce the density of free submicelles.

Alcohols↗