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PubMed1984

Localization of glycosylated kappa-casein on thin sections of casein micelles by lectin-labelled gold markers.

The location of the glycosylated part of kappa-casein in bovine casein micelles was investigated using gold particles (6 nm in diameter) labelled with Ricinus communis lectin and Limulus polyphemus lectin. The pattern of marking of thin sections of micelles was similar with both lectins. Glycosylated kappa-casein was distributed uniformly throughout most micelles of all sizes. Peripheral location of glycosylated kappa-casein was observed only occasionally in some of the largest micelles. Quantitative data indicated that the concentration of the glycosylated protein was constant in micelles of increasing sizes. As larger micelles contain less total kappa-casein than smaller ones, these data indicated that a greater proportion of their kappa-casein is glycosylated. These results support models for casein micelle structure where kappa-casein is distributed throughout the micelles. They do not agree with "coat-core" structures.

Animals↗
PubMed1989

Specificity determinants of maize casein kinase-IIB are related to but distinct from those of rat liver casein kinase-2.

The site specificity of maize seedling casein kinase-IIB, a type-2 casein kinase exhibiting an unusually low Mr, has been studied with the aid of model acidic peptide substrates for rat liver casein kinase-2. Like the animal enzyme, casein kinase-IIB also readily phosphorylates peptides SEEEEE, SEAEEE and SEEEAE, but not SEEAEE. Maize seedling casein kinase-IIB, however, is almost inactive toward peptides SAEEEE, SAEEEEE and SAAEEEEE which are good substrates for liver casein kinase-2. This indicates that casein kinase-IIB requires acidic residues not only at position +3, similar to rat liver casein kinase-2, but also at position +1, where the animal enzyme tolerates a neutral residue. This and other differences outlined in this report support the view that protein kinases of the same type from different sources may have significant differences in their substrate specificity.

Amino Acid Sequence↗
PubMed2001

Caseins and casein hydrolysates. 1. Lipoxygenase inhibitory properties.

Whole casein from bovine origin, the different casein subtypes alpha, beta, and kappa, and the related dephosphorylated proteins were assayed as modulators of soybean lipoxygenase 1 activity and were found to inhibit it. To define the lipoxygenase inhibitory domain, whole casein and beta-casein were digested by proteases (trypsin, clostripain, and subtilisin). The beta-casein tryptic digest and the tryptic and subtilisin digests of whole casein retained their inhibitory properties. The tryptic beta-casein digest was the most potent inhibitor of lipoxygenase activity and was further fractionated by FPLC or HPLC. The collected peptides inhibited the lipoxygenase-catalyzed reaction to different extents. The active fractions were analyzed by ESI-MS, and the sequences of several lipoxygenase inhibitory peptides, corresponding mainly to the C-terminal moiety of beta-casein, were identified.

Amino Acid Sequence↗
PubMed2006

Disruption and reassociation of casein micelles under high pressure: influence of milk serum composition and casein micelle concentration.

In this study, factors influencing the disruption and aggregation of casein micelles during high-pressure (HP) treatment at 250 MPa for 40 min were studied in situ in serum protein-free casein micelle suspensions. In control milk, light transmission increased with treatment time for approximately 15 min, after which a progressive partial reversal of the HP-induced increase in light transmission occurred, indicating initial HP-induced disruption of casein micelles, followed by reformation of casein aggregates from micellar fragments. The extent of HP-induced micellar disruption was negatively correlated with the concentration of casein micelles, milk pH, and levels of added ethanol, calcium chloride, or sodium chloride and positively correlated with the level of added sodium phosphate. The reformation of casein aggregates during prolonged HP treatment did not occur when HP-induced disruption of casein micelles was limited (<60%) or very extensive (>95%) and was promoted by a low initial milk pH or added sodium phosphate, sodium chloride, or ethanol. On the basis of these findings, a mechanism for HP-induced disruption of casein micelles and subsequent aggregation of micellar fragments is proposed, in which the main element appears to be HP-induced solubilization of micellar calcium phosphate.

Animals↗
PubMed2003

Casein enhances stability of peptides in intestinal lumen: role of digested products of casein.

PURPOSE: To investigate the inhibitory activity of casein on proteases in detail, the effect of digested products of casein itself on trypsin and chymotrypsin in rat small intestine was examined. METHODS: Male Sprague-Dawley rats weighing 200-300 g were used as the animal model. The luminal content of the jejunum was prepared, and the enzymatic activities of trypsin and chymotrypsin were determined using a specific substrate for each protease. Then, the effect of enzymatic digested products of casein on them was examined. RESULTS: The inhibitory activity of trypsin-digested casein against trypsin decreased as its digestion proceeded, but its inhibitory activity against chymotrypsin came to be more effective. On the other hand, the inhibitory activity of chymotrypsin-digested casein against chymotrypsin decreased with the degree of digestion, but no change in the inhibitory activity against trypsin was observed. Even the completely digested products of casein with trypsin or chymotrypsin showed inhibitory activities against the two proteases. CONCLUSIONS: It was suggested that not only the intact casein but also the products digested with trypsin or chymotrypsin contribute to the inhibitory effect of casein on the proteases in the intestinal lumen.

Animals↗
PubMed1994

beta-Casein mRNA sequesters a single-stranded nucleic acid-binding protein which negatively regulates the beta-casein gene promoter.

beta-Casein gene expression in mammary epithelial cells is under the control of the lactogenic hormones, glucocorticoids, insulin, and prolactin. The hormonal control affects gene transcription, and several regulatory elements in the beta-casein gene promoter between positions -80 and -221 have previously been identified. A region located in the promoter between positions -170 and -221 contains overlapping sequences for negative and positive regulatory elements. A sequence-specific single-stranded DNA-binding factor (STR), composed of two proteins with molecular masses of 35 and 54 kDa, recognizes the upper strand of this region and has a repressing role in transcription. High-level STR binding activity was observed in nuclear extracts from mammary glands of pregnant and postlactating mice and from noninduced HC11 mammary epithelial cells, cells with a low level of transcriptional activity of the beta-casein gene. STR activity is downregulated in mammary epithelial cells during lactation of the animals and after lactogenic hormone induction of HC11 cells in culture. These cells strongly transcribe the beta-casein gene. We investigated the mechanism of downregulation and found that a lactogenic-hormone-induced molecule (I-STR) inhibits STR from binding to its DNA target. I-STR is composed of RNA. STR is sequestered into the cytoplasm by I-STR after lactogenic hormone induction of mammary epithelial cells and remains present in an RNA-bound form. A high-affinity STR binding site was found in the 5' untranslated region of beta-casein mRNA. We propose that beta-casein mRNA can function as I-STR. beta-Casein mRNA may positively regulate its own transcription by translocating STR from the nucleus to the cytoplasm. The beta-casein STR binding sequence increases expression of a transfected beta-galactosidase gene when it is placed into the 5' untranslated region sequence of the mRNA. STR may have a positive role in posttranscriptional regulation.

Animals↗
PubMedDate not supplied

Influence of casein and casein hydrolysate diets on nutritional recovery of starved rats.

BACKGROUND: The aim of this study was to compare the effects of two diets, which differed in their protein source (casein and casein hydrolysate), on the nutritional recovery and intestinal repair of undernourished rats at weaning after a 3-day fasting period. Profound alterations in gut structure and signs of malnutrition appeared after the starvation period. METHODS: The casein hydrolysate was prepared by enzymatic hydrolysis and ultrafiltration. Rats were refed the casein-based or the casein hydrolysate-based diet for 96 hours. Normal-fed male Wistar rats at weaning were given the casein diet for 7 days and were used as controls. Liver acetylcholinesterase, glutamate dehydrogenase activities, serum amino acid profiles, jejunal oligosaccharidases, alkaline phosphatase, and leucine aminopeptidase activities were studied. Intestinal permeability to intact proteins was also tested by using ovalbumin and measuring its concentration in serum. RESULTS: Intestinal and liver enzyme activities and serum amino acid profiles reached normal values after 96 hours of refeeding, regardless of the diet used. Glutamate dehydrogenase activity remained higher in both diet groups. Intestinal permeability to ovalbumin remained significantly increased only in the group refed the casein diet. CONCLUSIONS: Our results show that 4 days of refeeding are sufficient for complete intestinal recovery after fasting, provided the dietary protein source is a casein hydrolysate. We suggest that patients with malnutrition or malabsorption syndrome should be fed formula composed of enzymatic protein hydrolysates (because of their low antigenicity) rather than enteral formulas composed of intact proteins.

Acetylcholinesterase↗
PubMed1999

Changes in the kappa-casein and beta-casein concentrations in human milk during lactation.

A microparticle-enhanced nephelometric immunoassay was developed for kappa-casein quantification in human milk. Together with a previously reported beta-casein comparable immunoassay, it was applied to 862 samples milk, collected from 82 mothers, to investigate the changes in casein concentrations in human milk during the first twelve weeks of lactation. kappa-casein immunoassay is sensitive (detection limit in the reaction mixture, 0.02 mg/L) and can be performed in diluted milk, excluding any interference or sample pretreatment. It allowed the quantitation of kappa-casein over a large range of concentrations (0.14-4.56 g/L) with accuracy and precision (coefficients of variation from 3 to 10%). beta- and kappa-casein concentrations and percentages among milk total proteins increase between colostrum (2.6 g/L, 14.3% and 1.2 g/L, 6. 5%, respectively) and transitional milk (4.4 g/L, 33.2% and 1.3 g/L, 9.5%), decrease at different rates from the third to the eighth week, then remain stable at least up to the end of the third month of lactation (2.7 g/L, 25.3% and 0.9 g/L, 8.5%). The beta-casein/kappa-casein ratio is higher in colostrum (0.61) than in transitional and mature milk (0.30) and could be related to a better digestibility of colostrum casein micelles by the neonate during the first days of life.

Antibodies↗
PubMed1989

A newly synthesized selective casein kinase I inhibitor, N-(2-aminoethyl)-5-chloroisoquinoline-8-sulfonamide, and affinity purification of casein kinase I from bovine testis.

When screening various isoquinolinesulfonamide compounds which we synthesized, CKI-7, N-(2-amino-ethyl)-5-chloroisoquinoline-8-sulfonamide, was found to have a potent inhibitory action against casein kinase I and a much weaker effect on casein kinase II and other protein kinases. Kinetic analysis indicated that CKI-7 inhibited casein kinase I competitively with respect to ATP and that the Ki values were 8.5 microM for casein kinase I and 70 microM for casein kinase II. An affinity chromatography absorbent was synthesized by coupling CKI-8 (1-(5-chloroisoquinoline-8-sulfonyl], a derivative of CKI-7, to cyanogen bromide-activated Sepharose 4B. Partially purified casein kinase I from bovine testis was subjected to affinity chromatography. Analysis of the purified casein kinase I by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate revealed a single band with molecular weight 37,000. These newly synthesized compounds, CKI-7 and CKI-8, should serve as useful tools for elucidating the biological significance of casein kinase I-mediated reactions.

Animals↗
PubMed1997

A Comparison of the Functional and Interfacial Properties of beta-Casein and Dephosphorylated beta-Casein

The functional and interfacial properties of beta-casein and dephosphorylated beta-casein (DeP beta-casein) were studied at pH 7.0 in 10 mM phosphate buffer. A decrease in emulsion stability and an increase in foamability was observed. Results from a variety of interfacial techniques including electrophoretic mobility, thin film thickness, surface and interfacial tension, surface rheology, adsorbed layer thickness, and adsorption isotherms of dephosphorylated beta-casein and beta-casein are reported. The results demonstrate that the phosphorylated groups of the N-terminal region of beta-casein are important for stabilizing emulsions. This is either as a direct result of charge repulsion between beta-casein N-terminal regions or more probably as an indirect result of the reduced N-terminal charge permitting DeP beta-casein to adopt a different interfacial conformation resulting in a loss or reduction of a steric barrier. Copyright 1997 Academic Press. Copyright 1997Academic Press

Journal Article↗
PubMed1993

Amyloid beta-protein stimulates casein kinase I and casein kinase II activities.

Amyloid beta-protein (A beta) is the major protein of cerebrovascular and plaque amyloid in Alzheimer's disease (AD). Extensive evidence has demonstrated abnormal protein phosphorylation in this disease. We investigated the effect of synthetic A beta with the amino-acid sequence corresponding to cerebrovascular A beta and plaque A beta on the activities of casein kinase I (CK I) and casein kinase II (CK II). These enzymes were purified from bovine brain and casein was used as a substrate. A beta was found to stimulate markedly CK I- and CK II-mediated phosphorylation of casein in a concentration-dependent manner. The effect of plaque A beta was considerably higher than that of cerebrovascular A beta. Heparin, which is known to be a specific inhibitor of CK II, completely inhibited A beta-stimulated CK II activity. A beta itself was not a substrate for casein kinases. These findings were confirmed using other substrates for CK I and CK II. The experiments with synthetic CK II-substrate peptide (Leu-Glu-Leu-Ser-Asp-Asp-Asp-Asp-Glu) and the phosphorylation of erythrocyte membrane proteins by intrinsic membrane-bound CK I in erythrocytes showed marked stimulation in activities of casein kinases in the presence of A beta 1-40 or blocked A beta. We propose that A beta, by stimulating casein kinases, may contribute to abnormal protein phosphorylation in AD, in particular to increased phosphorylation of microtubule-associated proteins, leading to the neurofibrillary tangles formation and neurodegeneration in this disease. Interaction of A beta with protein kinases, thus, may characterize the beginning of the disease.

Amino Acid Sequence↗
PubMed1984

Localization of kappa-casein on thin sections of casein micelles by the gold method.

The ultrastructural location of kappa-casein in bovine casein micelles was investigated by the protein A-gold method. Casein micelles, fixed in glutaraldehyde, were embedded at low temperature to enhance immunocytochemical marking of thin sections. kappa-Casein was found distributed throughout the micelles of all sizes with a higher concentration in the smaller micelles. No peripheral location of kappa-casein was observed, even in the larger micelles. These results do not agree with "coat-core" structures proposed for casein micelles. However they favor models where kappa-casein is distributed uniformly throughout the micelles.

Animals↗
PubMed1978

Role of prolactin and glucocorticoids in the expression of casein genes in rabbit mammary gland organ culture. Quantification of casein mRNA.

Milk synthesis is initiated solely by prolactin in the pseudopregnant rabbit and glucocorticoids potentiate this action of prolactin. In organ culture, prolactin, in the presence or in the absence of insulin, enhances casein synthesis and cortisol (inactive alone) amplifies this action. Measurements of casein mRNA concentration in total cellular RNA, by hybridization with DNA complementary to casein mRNA, revealed that the stimulation of casein synthesis by the glucocorticoid is accompanied by an increase in the amount of casein mRNA. A systematic comparison of variations of these two parameters indicated that the major effect of glucocorticoids on lactogenesis in the rabbit at this stage of mammary gland development is mediated through an increase in the quantity of casein mRNA available for translation. No simultaneous control of casein mRNA translation by cortisol was observed.

Animals↗
PubMed1975

Regulation of casein synthesis in the rabbit mammary gland. Titration of mRNA activity for casein under prolactin and progesterone treatments.

Total polysomal RNA or poly(A)-containing RNA isolated from membrane-bound polysomes of normal lactating rabbits directed the synthesis of casein in a reticulocyte lysate. Casein was identified by immunoprecipitation followed by SDS-polyacrylamide gel electrophoresis of the immunoprecipitate. The poly(A)-containing RNA was heterogeneous with one major peak corresponding to a 12-S sedimentation coefficient as determined by polyacrylamide gel electrophoresis. Using the same procedure, mRNAs isolated from the non-secreting tissue of pseudopregnant rabbits were found not to contain the 12-S peak and were unable to direct the synthesis of casein in vitro. Prolactin injected into pseudopregnant rabbits induced the synthesis of proteins immunoprecipitable by anti-casein anti-serum and induced the simultaneous appearance of the 12-S mRNA. Progesterone injected with prolactin prevented the induction of casein synthesis and the appearance of mRNA for casein. A close relationship was established between the ability of the tissue to synthesize immunoprecipitable casein and the corresponding mRNA content of polysomes.

Animals↗
PubMedDate not supplied

Molecular basis of IgE cross-reactivity between human beta-casein and bovine beta-casein, a major allergen of milk.

Twenty patients allergic to cow's milk proteins and with high levels of specific IgE directed against bovine whole casein were selected to evaluate reactivity of their IgE antibodies with human beta-casein. Highly purified human and bovine beta-caseins were prepared by selective precipitations and FPLC separation. Their identity and purity were assessed by HPLC, analysis of amino acid composition, sequencing of the five N-terminal amino acid residues and immunochemical tests. Direct and indirect ELISAs were performed using human and bovine beta-casein coated into microtiter plates and monoclonal anti-human IgE antibody AChE labelled for revelation. Seven sera contained specific IgE directed against human beta-casein. Inhibition studies using native human and bovine beta-caseins as well as bovine beta-casein-derived peptides demonstrated that, depending on the sera, one or several common epitopes located in different parts of the molecule were shared by the two homologous proteins.

Adolescent↗
PubMed1991

Enzymic modification of alpha s1-casein with peptidylarginine deiminase: preparation of less acid-coagulable and less calcium-sensitive casein.

Enzymic modification with peptidylarginine deiminase (EC 3.5.3.15) enabled five out of six arginyl residues in alpha s1-casein to be converted to citrullyl residues, only the N-terminal arginyl residue remaining unaffected. An increase in the net negative charge was confirmed by PAGE. The isoelectric point was decreased from 4.46 for the intact alpha s1-casein to 4.30 for the deiminated type, while simultaneously lowering the acid-precipitation starting point from pH 5.17 to pH 4.62. The deiminated alpha s1-casein self-associated less in the absence of Ca and was less Ca-sensitive than the native type, although its Ca-binding ability was slightly enhanced. In the presence of 25 mM-CaCl2 and kappa-casein, Ca-induced precipitation of alpha s1-casein did not occur, the solution of the mixture remaining transparent. Deimination of alpha s1-casein resulted in altering its characteristics, possibly by interfering with interactions through hydrophobicity and/or hydrogen bonding. The positive charge of the arginyl residues might play an important role in casein micelle formation.

Amino Acids↗
PubMed2004

Effects of casein and fat content on water self-diffusion coefficients in casein systems: a pulsed field gradient nuclear magnetic resonance study.

The water self-diffusion coefficients in casein matrixes were measured using a pulsed field gradient spin-echo nuclear magnetic resonance technique (PFG-SE NMR). The dependence of the water self-diffusion coefficient on the casein concentration and the aqueous phase composition is reported in both a rehydrated native phosphocaseinate dispersion and a concentrated casein retentate. A model has been proposed to explain the different behavior of the water self-diffusion coefficient in the two casein systems. This model demonstrates that the water self-diffusion cannot be simply explained by the water content only. So, taking into account the specific effect of each constituent of the aqueous dispersing phase, the water self-diffusion reduction induced by the casein micelle can be modeled. The effect of fat on the water self-diffusion coefficients was investigated. Anhydrous milk fat-reconstituted retentate samples were used in order to estimate the obstruction effect of fat globules in the modeling process. The dependence of the self-diffusion coefficient of water on the fat and casein content is reported. A general model included the effect of the aqueous phase composition, and the obstruction effects of casein micelles and fat globules were proposed. This model was validated for water self-diffusion coefficients in industrial fatty retentates.

Caseins↗
PubMed2003

Cloned transgenic cattle produce milk with higher levels of beta-casein and kappa-casein.

To enhance milk composition and milk processing efficiency by increasing the casein concentration in milk, we have introduced additional copies of the genes encoding bovine beta- and kappa-casein (CSN2 and CSN3, respectively) into female bovine fibroblasts. Nuclear transfer with four independent donor cell lines resulted in the production of 11 transgenic calves. The analysis of hormonally induced milk showed substantial expression and secretion of the transgene-derived caseins into milk. Nine cows, representing two high-expressing lines, produced milk with an 8-20% increase in beta-casein, a twofold increase in kappa-casein levels, and a markedly altered kappa-casein to total casein ratio. These results show that it is feasible to substantially alter a major component of milk in high producing dairy cows by a transgenic approach and thus to improve the functional properties of dairy milk.

Animals↗