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At least 1,621 records · Page 90Linked to original sources
PubMed1997

Binding ability of Cu2+ ions by opiate-like fragments of bovine casein.

The coordination modes of Cu(II) to alpha-casein (90-95) and alpha-casein (90-96) peptides with opioid activity isolated from pepsin hydrolisates of alpha-casein were investigated by means of electron paramagnetic resonance, absorption, and circular dichroism spectroscopy and potentiometry. The results allow the identification of the complex species involved and the attribution of the spectral data set to the various complex structures. According to the spectroscopic data, a phenolate side-chain of Tyr residue belonging to the Gly-Tyr-Leu or Gly-Tyr-Leu-Gln fragment of the peptides is involved in the metal coordination in a complex which is a minor species at neutral pH range.

Amino Acid Sequence↗
PubMed1997

Assays for the measurement of tissue transglutaminase (type II) mediated protein crosslinking via epsilon-(gamma-glutamyl) lysine and N',N'-bis (gamma-glutamyl) polyamine linkages using biotin labelled casein.

Two colorimetric assays for tissue transglutaminase (type II) activity involving the crosslinking of proteins have been developed. In one assay, biotin labelled casein is crosslinked into chemically modified casein bound to a microtiter plate by tissue transglutaminase and the biotin labelled reaction product is detected by conjugation to Extravidin peroxidase. The assay can detect activity in 10 ng of commercially available purified guinea pig liver transglutaminase and in the crude homogenate derived from 400 human endothelial cells (cell line ECV 304). A correlation (r2 = 0.977) was shown between this assay and the radiolabeled putrescine incorporation assay for the detection of transglutaminase activity. This assay measures the protein crosslinking activity of tissue transglutaminase as opposed to polyamine incorporation and offers a rapid, non-radiometric method for screening large sample numbers. Typical inter-assay variability is 13.9 +/- 1.5% (n = 8). In a second assay, the ability of tissue transglutaminase to catalyze the formation of N',N'-bis (gamma-glutamyl) polyamine bridges is measured. N',N'-dimethylcasein is bound to a microtiter plate and modified enzymatically using commercially available purified guinea pig liver transglutaminase to incorporate polyamines into glutamine residues. Biotin labelled casein is then crosslinked into the immobilized polyamines by tissue transglutaminase resulting in the formation of N',N'-bis (gamma-glutamyl) polyamine linkages.

Animals↗
PubMed1998

Isolation, characterization and disruption of the casein kinase II alpha subunit gene of Leishmania chagasi.

To elucidate the role played by casein kinase II in Leishmania survival, we have isolated and characterized the Leishmania chagasi casein kinase II alpha subunit cDNA, (L.c CKIIalpha). The 1083 bp coding region is flanked by 148 bp of 5' UTR and 1155 bp of 3' UTR. L.c CKIIalpha shows a remarkable degree of similarity with other isolated casein kinase II alpha subunit sequences. L.c CKIIalpha protein is encoded by a single copy gene that transcribes a mRNA of 2.4 kb. The 41.2 kDa L.c CKIIalpha protein expressed in vitro has been shown to be catalytically active. A single allele disruption of the L.c CKIIalpha gene that removes 94 bp from the coding region which contains one of the 15 conserved amino acids closest to the carboxy-terminus of the protein has been generated. This mutant is viable and results in a reduction of L.c CKIIalpha transcript levels over 14-fold and that of an iron superoxide dismutase mRNA by 5-fold. As well, the kinase activity of the single allele disrupted cells showed a 3-fold reduction as compared to the wild type cells suggesting a decrease in activity of the L.c CkIIalpha enzyme.

Alleles↗
PubMed2002

Involvement of Oct-1 in transcriptional regulation of beta-casein gene expression in mouse mammary gland.

Mouse beta-casein gene promoter contains a region termed block C which is crucial for its gene transcription induced by lactogenic hormones. Nuclear extracts from mouse mammary glands contain at least two binding complexes (DS1 and DS2) which specifically bind to double-stranded block C region DNA. The binding sequence of these complexes was identified to be 5'-AAATTAGCATGT-3' which contains a sequence element related to the consensus octamer motif's complement ATTTGCAT. In the present study, we demonstrate that this sequence element indeed is the binding site for octamer-binding transcription factors (Octs) and Octs represent the double-stranded DNA binding proteins specifically binding to the block C region. Formation of the specific double-stranded binding complexes can be completely blocked by Oct binding motif oligonucleotides and anti-rOct-1 antiserum. We also show that Oct-1B represents at least partial, if not all, double-stranded binding protein, DS1, in mammary nuclear extract. Oct-1B may function as a transcriptional activator on casein gene promoter. The Oct binding activity to beta-casein gene promoter in the mammary gland is affected under influence of hormones both in vitro and in vivo. The DS1 binding activity can be induced by the combination of lactogenic hormones insulin, hydrocortisone and prolactin in organ culture of virgin mouse mammary gland. The binding activity in vivo can be induced by injection of progesterone or its combination with estradiol in virgin mice.

Animals↗
PubMed2002

Type IV phosphodiesterase activity specifically regulates cAMP-stimulated casein secretion in the rat mammary gland.

This study investigates the regulation of cAMP-stimulated casein secretion in rat mammary explants by cAMP phosphodiesterase (cAMP-PDE) activity. cAMP-PDE activity of the lactating rat mammary gland is shown to be provided by three families, types II, III and IV. In mammary explants, general inhibition of the cAMP-PDE activity significantly increased the rate of cAMP-stimulated casein secretion. This effect could be mimicked using the type-IV specific inhibitor rolipram but not by the specific, or combined, inhibition of the type II and type III activity. Only type IV activity significantly affected intracellular accumulation of cAMP whereas all three cAMP-PDE activities were shown to influence the PKA activation ratio in cells. RtPCR analysis showed that the mammary gland apparently expresses just three type IV isozymes, RNPDE4A5, RNPDE4A8 and RNPDE4D3. A specific role for type IV cAMP-PDE activity in the regulation of casein secretion is suggested and possible mechanisms for the effects of PDEIV activity discussed.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1999

Oral administration of hot water extracts of Chlorella vulgaris reduces IgE production against milk casein in mice.

Hot water extract of Chlorella vulgaris (CVE) is a biological response modifier (BRM) which enhances resistance to Listeria monocytogenes through augmentation of helper T cell type 1 (Thl) responses producing gamma-interferon (gammaIFN). We show here that oral administration of CVE in mice suppressed the production of immunoglobulin (Ig)E against casein antigen accompanied by increased gammaIFN and IL-12 mRNA expression. Oral administration of CVE enhanced Thl response to casein in the spleen of casein immunized mice. CVE may be useful for prevention of allergic diseases with a predominant Th2 response.

Administration, Oral↗
PubMed2000

Dephosphorylation-induced structural changes in beta-casein and its amphiphilic fragment in relation to emulsion properties.

To promote the understanding of the relationship between emulsifying and molecular properties of proteins/peptides, intact beta-casein (betaCN) and its amphipathic fragment, i.e., betaCN (1-105/107) were dephosphorylated. Dephosphorylation was found not to change significantly their emulsifying properties. Since it is known that the structure of proteins can change upon adsorption onto an interface, the secondary structure of intact beta-casein, its amphipathic fragment, and their dephosphorylated forms, both in solution and after adsorption onto a hydrophobic teflon/water interface, were studied by far-UV circular dichroism spectroscopy. An increased content of secondary structure, especially alpha-helix, was found for all samples after adsorption onto teflon. Dephosphorylation increased the helix-forming propensity, especially for amphipathic fragment of beta-casein. No influence of the secondary structure properties on the emulsion-forming and -stabilizing properties was observed, but a relationship between the maximum surface load and the emulsion-stabilizing properties was found.

Caseins↗
PubMed1998

Casein peptide release and passage to the blood in humans during digestion of milk or yogurt.

In adult humans, after milk or yogurt ingestion, many peptides derived from alpha s1-, beta- or kappa-caseins were detected in stomach, including the kappa-caseinoglycopeptide, an inhibitor of platelet aggregation. Smaller peptides derived from casein and lactoferrin were recovered from duodenum. Two long peptides, the kappa-caseinoglycopeptide and the N-terminal peptide of alpha s1-casein, were absorbed and detected in plasma. These results support the concept that food-born peptides could have physiological activities in man.

Adult↗
PubMed2002

Charge transfer between tryptophan and tyrosine in casein: a pulse radiolysis study.

Charge transfer from tyrosine to tryptophan radicals in bovine milk casein, as observed using pulse radiolysis technique, is reported. The reactions of casein with hydroxyl, azide, Br(2)(*-) and CCl(3)O(2)(*) radicals have also been studied. Radical transformation was found to take place at a rate of 1.5 x10(4) s(-1). The effect of pH, oxidising radical and the proximity of tyrosine and tryptophan on this radical transformation, as well as repair of the casein radical by ascorbate, have also been studied.

Caseins↗
PubMed1979

Simultaneous production of casein and mammary tumor virus in mouse mammary epithelial cells grown on floating collagen gels.

Simultaneous production of casein and mammary tumor virus (MTV) was analyzed in monolayer cultures of mammary epithelial cells from pregnant BALB/cfC3H mice. A comparison of the 2 cell culture substrata, plastic culture dish and floating collagen gel, showed that the latter supported a much higher degree of simultaneous casein and MTV production in the presence of insulin, cortisol and prolactin in serum-free culture medium. Importance of floating collagen gel was further shown by delaying the flotation of gels. When the release of gels was delayed, there were concomitant delays in the increase of casein and MTV production. These results indicate that hormones, nature of substratum and flotation regulate the degree of differentiation of mammary epithelial cells in vitro.

Animals↗
PubMed1997

Antimutagenic activity of casein against MNNG in the E. coli DNA repair host-mediated assay.

The effect of caseinate and soy protein in the diet on the mutagenicity induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) was assessed in-vivo and ex-vivo in the DNA-repair host-mediated assay and liquid suspension assay, respectively. Of the two proteins only casein showed a strong antimutagenic activity over the whole digestive tract, except in the stomach. It is suggested that the molecular structure of a protein determines its protective effect against mutagens: casein lacks secondary and tertiary structure so that amino acids are more readily available for interaction with the mutagen than with the amino acids in soy protein which is a globular protein.

Animals↗
PubMed1979

A genetic and biochemical analysis of a polymorphism of bovine alpha S2-casein.

Using gel electrophoresis a genetic polymorphism of alpha S2-casein (Cn) was discovered in individual milk samples from 2 bovine breeds of the eastern part of France (Vosgienne and Montbéliarde). The 3 observed phenotypes (Plate 1) are determined by 2 co-dominant alleles at an autosomal locus. The alpha S2-Cn A variant was the only one known up to now in European breeds (reference variant) and alpha S2-Cn D is a new variant, whose bands overlap the beta-casein A band at pH 8.6, and migrate faster than alpha S2-Cn A at pH 3.0. The sequence of the polypeptide chain alpha S2-Cn D differs from that of alpha S2-Cn A by the deletion of a very acidic nonapeptide, which includes a cluster of 3 phosphoseryl residues. Due to the characteristics of the reference sequence, this deletion cannot be exactly located but it involves residues 50-58, or 51-59, or 52-60. A genetic analysis shows that locus alpha S2-Cn is closely linked to the cluster alpha S1-Cn--beta-Cn--kappa-Cn. The 4 casein species are thus synthesized by 4 closely linked loci.

Alleles↗
PubMed1979

Quantitation of alpha S1-casein aggregation by the use of polyfunctional models.

A model for the coagulation of Ca2+ alpha S1- caseinate is described wherein the casein molecules are considered to aggregate as polyfunctional units. The functionalities on the protein molecules are produced as a consequence of the binding of Ca2+, and the multiple equilibria which are established during this binding produce a distribution in which not all casein molecules have the same functionality. The theory is compared with experimental data of the precipitation reaction, and is shown to provide an adequate quantitative description of the precipitation.

Calcium↗
PubMed1979

Casein micelles: the colloid-chemical approach.

The colloidal properties of micellar casein are reviewed. It is shown that behaviour of intact micelles is much at variance with the predictions from the Schulze-Hardy rule, and that therefore their stability cannot be explained by the principles of the DLVO theory. Towards electrolyte, micelles behave as a protein rather than a lyophobic colloid. Casein is a strong protective colloid. In the micelle, however, it does not completely cover the inorganic constituent which remains sensitive to changes in the ionic environment. The rate theory of the enzyme-induced clotting of casein micelles is summarized. It is shown that the lag phase in the clotting is due to the second order of the co-agulation reaction. Flocculation rate constants of micelles have been deduced from clotting times. Their relatively low values can be attributed to an orientational constraint. Practical consequences of the theory with respect to clot structure, gelation of sterilized products and cheese manufacture are discussed.

Caseins↗
PubMed1979

Developments in column chromatography for the separation and characterization of casein micelles.

Skim-milk was fractionated by permeation chromatography on CPG-10 (300 nm) at 20 degrees C with synthetic milk serum. The elution profile, which was highly reproducible, showed 3 partly resolved peaks. On treatment with 0.1% glutaraldehyde before chromatography, a similar profile was obtained indicating no appreciable micellar dissociation during chromatography of the milk. The casein composition of the eluent fractions, determined by quantitative chromatography on hydroxyapatite, showed that 12.1% of total casein was associated with the low molecular weight peak. The micelle content of beta- and kappa-casein increased with increasing elution volume, and the alphas/kappa ratio showed a progressive diminution from 4.3 to 2.3. Large differences were found in the colloidal phosphate contents and the weight average diameters of the micelle fractions which clearly show that CPG-10 fractionates on the basis of molecular size.

Animals↗
PubMed1979

CPG-chromatography studies of the stability of casein micelles.

Casein micelles fractionated on controlled pore glass (CPG-10/3000) were shown to be stable by recycling experiments. Only minor effects on the size distribution of the casein micelles were found after heating skim-milk to 100 degrees C for 10 min, or freeze-drying skim-milk at -70 degrees C followed by resuspension in the synthetic milk serum of Jenness & Koops (1962). The heating caused some whey proteins (beta-lactoglobulin) to enter the micelle fractions while the freeze-drying caused some of the largest micelles to disrupt. In colloidal calcium phosphate-free skim-milk prepared according to Pyne & McGann (1960) all the micelles appeared to dissociate into monomeric caseins.

Animals↗
PubMed1982

Factors affecting the distribution of lipoprotein lipase activity between serum and casein micelles in bovine milk.

The influence of mastitis and early lactation, and the effect of treating milk with heparin, blood serum and trypsin, on the proportion of lipoprotein lipase (LPL) activity in mild serum was investigated. The relative importance of milk serum LPL and LPL bound to micellar casein in promoting lipolysis was also examined. Colostrum contained LPL activity, 45% of which was found in the serum phase in samples obtained from the first milking post partum, but this value fell to 34% in samples taken 24 h later. The proportion of serum LPL was also increased in milks from quarters infected with Staphylococcus aureus, but not after overnight treatment of normal milk at 4 degrees C with 5% (w/v) blood serum or 2 microgram/ml trypsin. The addition of 5 microgram/ml heparin resulted in a consistent increase in serum LPL which varied between 14 and 50% of total milk LPL. Heparin did not release all the enzyme bound to casein micelles even after a second heparin treatment of resuspended micelles. Serum LPL was more effective in promoting lipolysis and was more responsive to blood serum activation than LPL bound to casein micelles. Lipolysis increased after heparin treatment but the increase was not related to serum LPL activity.

Animals↗
PubMed1989

Biologically active casein peptides implicated in immunomodulation.

Maternal milk should not only be considered as a nutrient, but also as a protecting agent against aggressions from the neonate's new environment. Breast-feeding facilitates transmission of a passive immunity by multifunctional factors which have a direct effect on the neonate's resistance to bacterial and viral infections. Among these factors are the main milk proteins, the caseins: during enzymic digestion of human and bovine caseins, immunomodulating peptides are released. Corresponding synthetic peptides stimulated in vitro phagocytic activity of murine and of human macrophages and exerted in vivo a protective effect against Klebsiella pneumoniae infection of mice. These data suggest that casein peptides may exert a stimulating function on the immune system of the newborn.

Animals↗