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PubMed1996

Hormone-dependent expression of gamma-casein mRNA in mouse mammary epithelial cells cultured on floating collagen gels.

Mammary epithelial cells isolated from pregnant mice were plated on a collagen gel matrix and cultured in a serum-free medium supplemented with combinations of insulin, dexamethasone and prolactin (PRL). After the cells formed a monolayer, the collagen gel was detached from the culture dish and allowed to float in the medium. Quantification of gamma-casein mRNA by a competitive PCR method revealed that the cells on the floating gel accumulated considerably larger amounts of gamma-casein mRNA than the cells on the gel remained attached to the dish. Under these floating collagen gel culture conditions, addition of both dexamethasone and PRL to the insulin-supplemented basal medium maximally stimulated the accumulation of gamma-casein mRNA. These observations strongly suggest that the status of the extracellular matrix as well as hormones controls the differentiation of mouse mammary epithelial cells at the mRNA level.

Animals↗
PubMed1991

The effects of abomasal casein infusions in growing beef steers on portal and hepatic flux of pancreatic hormones and arterial concentrations of somatomedin-C.

The net release of insulin, glucagon and somatostatin by the portal-drained viscera (PDV) and their net uptake by the liver in response to 3-d abomasal infusions of casein were measured in seven multicatheterized beef steers. The steers were fed 4.3 kg DM/d of a high-concentrate diet in 12 equal meals (13.1 Mcal ME/d and 95 g N/d). In two separate experiments, the abomasal infusion of 300 g casein/d (300C) or 150 g casein/d (150C) was compared to a water infusion. Plasma flow was measured by indicator dilution and net flux by venoarterial concentration difference x plasma flow. Arterial plasma concentrations of insulin were increased (P less than .02) by either 300C or 150C. The 300C increased (P less than .03) PDV insulin release but did not affect hepatic uptake, resulting in an increased (P less than .03) total splanchnic (TSP) insulin flux. The 300C increased (P less than .05) plasma concentrations of glucagon as the result of decreased (P less than .06) hepatic extraction ratio and not as the result of increased portal release. The portal and hepatic flux of somatostatin measured as somatostatin-like immunoreactivity (SLI) were highly variable and not affected by casein infusions. Arterial plasma concentrations of somatomedin-C were not responsive to abomasal casein infusions. The abomasal infusion of 300C resulted in increased plasma concentrations of insulin via increased PDV release and increased plasma glucagon via decreased hepatic extraction ratio.

Abomasum↗
PubMed1991

The net portal and hepatic flux of metabolites and oxygen consumption in growing beef steers given postruminal casein.

Changes in net portal and hepatic nutrient flux and oxygen consumption in response to 3-d abomasal casein infusions were studied in seven multicatheterized beef steers. Steers were fed 4.3 kg DM/d of a high-concentrate diet in 12 equal meals. Blood flow (para-aminohippurate dilution) and net flux (venoarterial concentration difference x blood flow) across portal-drained viscera (PDV) and hepatic tissues were measured on d 3 of the abomasal infusions. In two experiments, the response to 300 (300C) and 150 (150C) g casein/d were compared, respectively, to a control water infusion. The 300C increased (P less than .05) arterial blood concentrations of alpha-amino N (AAN), urea N and ammonia; 150C increased (P less than .05) arterial urea N. Urinary urea N excretion was increased (P less than .01) by 300C and 150C. Although 300C increased net PDV release of AAN (P less than .07) and alanine (P less than .10), there was no net change in total splanchnic (TSP) flux due to an increased net hepatic uptake of AAN (P less than .01) and alanine (P less than .05). Net PDV glucose flux was decreased (P less than .05) by 300C, but net hepatic glucose flux was not affected by either level of casein. The 150C increased TSP oxygen consumption (P less than .05) and hepatic oxygen extraction (P less than .10). Approximately 26 and 30% of the casein N infused abomasally appeared in the portal blood as AAN for 150C and 300C, respectively. The sum of net PDV ammonia and AAN fluxes accounted for 47 and 88% of the N infused for 150C and 300C, respectively. These data emphasize the importance of intestinal and liver tissues in regulating the flux of nitrogenous compounds absorbed from the diet.

Amino Acids↗
PubMed1999

Technical note: use of PCR-single-strand conformation polymorphism analysis for detection of bovine beta-casein variants A1, A2, A3, and B.

We have optimized the polymerase chain reaction-single-strand conformation polymorphism (PCR-SSCP) technique to screen the most frequent variants (A1, A2, A3, and B) of the bovine beta-casein gene. Five partly overlapping PCR products (233, 234, 265, 466, and 498 bp) of Exon VII of the beta-casein gene that encompass the target point mutations were heat-denatured, separated on nondenaturing polyacrylamide gels, and silver-stained. Simultaneous detection of all variants in reference samples of known genotypes (A1A2, A2A2, A1A3, A1B, and A2B) was best achieved on 17% polyacrylamide (100:1 acrylamide:bis-acrylamide ratio) gels with the PCR product of 234 bp. These results were confirmed by sequencing the allele-specific SSCP bands directly excised from polyacrylamide gels. A population of 65 anonymous samples belonging to various breeds was then analyzed twice, without discrepancies in a blind trial. Routine beta-casein genotyping using PCR-SSCP is proposed as a cost-effective, fast, and sensitive technique.

Animals↗
PubMed1999

Effects of increasing ruminally degraded nitrogen and abomasal casein infusion on net portal flux of nutrients in yearling heifers consuming a high-grain diet.

Seven Meat Animal Research Center (MARC) III heifers (410+/-25 kg) fitted with hepatic portal, mesenteric venous, carotid catheters, and an abomasal cannula were used in a 7 x 5 incomplete Latin square design experiment. The objective was to evaluate the effects of increasing levels of ruminally degradable N (RDN) with or without the addition of abomasally infused casein on portal-drained visceral (PDV) flux of nutrients. Treatments consisted of dietary CP percentage levels of 9.5 (control), control plus .72% dietary urea (11.5U), control plus 1.44% dietary urea (13.5U), control plus abomasally infused casein (250 g/d; 11.5C), or control plus .72% dietary urea and abomasally infused casein (250 g/d; 13.5UC). All diets contained (DM basis) 80% ground corn, 15% corn silage, and 5% dry supplement and were provided for ad libitum consumption. Nitrogen intake increased (linear, P < .001) as CP increased from 9.5 to 13.5%. Portal-drained visceral release of ammonia N increased (linear, P < .10) as RDN increased, and was greater (P < .05) when protein was fed compared with heifers fed control (P < .10). Urea N removal by PDV was not affected ( P > . 10) by level of RDN but was greatest when 11.5C was fed and least when 13.5UC was fed. Net alpha-amino N (AAN) release by PDV was greatest when 13.5UC was fed (309 mmol/h), least when 9.5% CP was fed (112 mmol/h), and intermediate for the other groups (205 to 252 mmol/h). These data suggest that removal of N by the PDV may promote microbial protein synthesis when dietary RDN is low. When RDN needs have been met and amino acids are deficient for the host, escape protein should be fed to increase amino acid absorption.

Abomasum↗
PubMed2006

True ileal amino acid digestibility and endogenous ileal amino acid losses in growing pigs fed wheat shorts- or casein-based diets.

Use of dietary AA in growing pigs reflects digestion and use of digested AA for various body functions. Before evaluating dietary effects on use of digestible AA intake for body protein deposition, a digestibility study was conducted to investigate true ileal AA digestibility and endogenous ileal AA losses in growing pigs fed graded levels of wheat shorts (WS) or casein (CS; control). A casein-based basal diet (basal) was formulated to contain 0.27 g of standardized ileal digestible (SID) Lys per MJ of DE, to which extra Lys was added from WS (WS2, +0.10 g of SID Lys per MJ of DE; WS3, +0.20 g of SID Lys per MJ of DE) or casein (CS3, +0.20 g of SID Lys per MJ of DE). A fifth diet was formulated to be similar in CP level and source as CS3 but in which 6% pectin, a source of soluble non-starch polysaccharides (NSP), was included at the expense of cornstarch (CS3 + pectin). Five Yorkshire barrows (17.5 +/- 1.5 kg of BW) were fitted with a T-cannula at the distal ileum and randomly assigned to 1 of the 5 experimental diets in a 5 x 5 Latin Square design. Apparent ileal digestibility (AID), true ileal digestibility (TID), and endogenous ileal protein losses (EPL) were determined using the homoarginine method. Diet CS level did not influence (P > or = 0.10) TID of most essential AA or EPL (10.4 g/kg of DM intake). Including pectin in the diet did not influence TID of AA (P > or = 0.10) but increased EPL (15.6 g/kg of DM intake; P > or = 0.01). Inclusion of WS in the diet reduced TID of most essential AA (P < 0.01). The TID values for most essential AA, however, were the same (P > or = 0.10) for both dietary WS levels, except for Lys and Met, which were further reduced at the greatest dietary WS level. Increased EPL (P < 0.01) was only observed for WS3 (16 g/kg of DMI). We concluded that (1) the effects of dietary protein source on AID of AA can be attributed both to reduced TID of AA and increased EPL, (2) the impact of dietary WS level on TID of AA and EPL does not seem to be linear, (3) soluble NSP from pectin or WS exerts a greater effect on EPL than insoluble NSP, and (4) because of the metabolic cost associated with EPL and the impacts of feed composition on microbial fermentation in the gut lumen, the effects of feed ingredients on the use of ileal digestible AA for protein deposition should be investigated further.

Amino Acids↗
PubMed2000

Molecular cloning and phylogenetic analysis of canine beta-casein.

A canine beta-casein cDNA was isolated from mammary tissue by polymerase chain reaction (PCR) using degenerate primers. It encodes 250 amino acids protein containing the conserved sequence motif of beta-casein. It showed the highest homology with snow-leopard (Uncia uncia (55-62% identity). It also showed 44-53% identity with human, 33-42%, identity with mouse, 29-37%, identity with rat, 43-53% identity with rabbit, 41-48% identity with pig, 44-51% identity with cattle and 44-50% identity with sheep. A 1.2-kb mRNA was detected in mammary tissue by Northern blot analysis. Phylogenetic analysis revealed that canine beta-casein formed a branch with lesser panda and snow leopard, which were grouped into carnivore.

Amino Acid Sequence↗
PubMed1999

Casein related amyloid, characterization of a new and unique amyloid protein isolated from bovine corpora amylacea.

Amyloid bodies can be found in mammary secretory tissue of various species. These corpora amylacea (CA) have a lamellated structure, contain amyloid fibrils and are predominantly located in the alveolar lumina. The nature of the amyloid was not known, but CA were suggested to originate either from milk casein or mammary alveolar epithelial keratin. In the present report, bovine CA were analyzed histochemically. Furthermore, CA were isolated, analyzed and the amyloid was purified and characterized by amino acid sequencing. CA amyloid appeared to be potassium permanganate sensitive and tryptophan positive, and in this respect different from most other amyloid types except for AA and beta-2 microglobulin amyloid. Gel filtration of purified amyloid fibrils showed a HMW peak and a major 4 kD peak. N-terminal amino acid sequencing showed the amyloid to consist of tryptic-like peptides with an unusually high content of amino acids with bulky side chains. The amyloid protein was identified as derived from alpha-S2-casein. The fragments are of varying length (32, 33 and 45 amino acids), but all start at position 81 of alpha-S2-casein. We have identified a new and unique amyloid protein, and we propose to designate it as A alpha-S2C according to the guidelines for amyloid nomenclature.

Amino Acid Sequence↗
PubMed2001

Colloidal calcium phosphates in casein micelles studied by slow-speed-spinning 31P magic angle spinning solid-state nuclear magnetic resonance.

The composition of bovine casein micelles was analyzed by 31P magic angle spinning solid-state nuclear magnetic resonance spectroscopy. By looking at isotropic and anisotropic 31P chemical shift parameters, resonance line shapes, the combination of single-pulse and 1H to 31P cross-polarization spectra, and comparison with spectra for various model compounds combined with multiple-component simulation and iterative fitting procedures, we were able to identify and quantify a variety of inorganic and organic phosphates in the micelles. These include phosphates from mobile and immobile inorganic hydroxyapatite-type phosphates as well as phosphates from kappa-casein and the Ca2+-binding phosphoserines from alphas1-, alphas2-, and beta-casein. This information is discussed in relation to previous knowledge and various models for the colloid formation.

Animals↗
PubMed2001

Secondary structure of bovine alphaS2-casein: theoretical and experimental approaches.

Circular dichroism and Fourier transform infrared spectroscopy of bovine alphaS2-casein both report a 24 to 32% content of alpha-helix. A consensus of sequence based predictions for alpha-helix suggests a Lys77-Gln91 helix within the sequence (Ser61-Arg125). This motif is repeated at (Ser143-Leu207), and this region contains a longer Thr145-Leu177 predicted alpha-helix. A short, seven-member alpha-helix may also organize the N-terminal peptide that precedes the first phosphoserine [-Srp-]3 cluster. As was found for other caseins studied by these spectroscopic methods, a high degree of extended beta-sheet (approximately 30%) and turns (25 to 30%) are predicted for alphaS2-casein.

Animals↗
PubMed2004

Gelation of casein-whey protein mixtures.

Heated milk consists of a mixture of whey protein-coated casein micelles and soluble whey protein aggregates. The acid-induced gelation properties of heated milk are consistently different from those of unheated milk--i.e., a shift in gelation pH, stronger gels, and a different microstructure of the gels. In this study we investigated the role of the different fractions of denatured whey proteins on the acid-induced gelation, the gel hardness, and the microstructure. Both whey protein fractions contribute to the observed shift in gelation pH, although by a different mechanism. Obtaining gels with high gel hardness occurs most effectively when all denatured whey proteins are present as whey protein aggregates. It was observed that disulfide bridge exchange reactions during the acid-induced gelation at ambient temperature play an important role for both whey protein fractions. Additionally, disulfide interactions seem to occur between the aggregates and the casein micelles during the gel state. In this study, we show the development of a new approach for confocal scanning laser microscopy measurements--i.e., separate staining of the proteins in milk. By using this method, we were able to determine that, although whey protein aggregates are not linked to the casein micelles, they nevertheless gel at the same moment. This work adds to a better understanding of the role of denatured whey proteins during acid-induced gelation and could improve the effective use of whey proteins.

Animals↗
PubMed2004

Single nucleotide polymorphisms in the ovine casein genes detected by polymerase chain reaction-single strand conformation polymorphism.

Casein genetic polymorphisms are important and well known due to their effects on quantitative traits and technological properties of milk. At the DNA level, polymerase chain reaction (PCR)-single-strand conformation polymorphism (SSCP) allows for the simultaneous typing of several alleles at casein loci, as well as the detection of unknown polymorphisms. Here we describe the usefulness of the PCR-SSCP technique for casein typing in sheep. In particular, three single-nucleotide polymorphisms (SNP) are described at CSN1S1, CSN2, and CSN3, all resulting in amino acid exchanges. At CSN1S1, a transition T-->C was found, resulting in the deduced amino acid exchange Ile186-->Thr186. A transition A-->G resulting in the deduced amino acid exchange Met183-->Val183 was identified at CSN2. The 2 SNP showed a rather high frequency (ranging from 0.12 to 0.26) in 3 Italian breeds (Sarda, Comisana, Sopravissana). Another transition C-->T (Ser104-->Leu104) was found at CSN3 in one heterozygous animal.

Alleles↗
PubMed2004

Release of short and proline-rich antihypertensive peptides from casein hydrolysate with an Aspergillus oryzae protease.

Angiotensin-I converting enzyme inhibitory activities were measured after hydrolysis of casein by 9 different commercially available proteolytic enzymes. Among these enzymes, a protease isolated from Aspergillus oryzae showed the highest angiotensin-I converting enzyme inhibitory activity per peptide. The A. oryzae peptide also showed the highest antihypertensive effect in spontaneously hypertensive rats when the systolic blood pressure was measured 5 h after oral administration of 32 mg/kg of various enzymatic hydrolysates. Significant antihypertensive effects were observed with dosages of 9.6, 32, and 96 mg of the A. oryzae peptide/kg of body weight (BW), and the effects were dependent on these peptide dosages. Analysis of peptide length showed the A. oryzae hydrolysate was the shortest of all tested casein hydrolysates; the peptide mixture had an average value of 1.4 amino acids (AA) in the sequence. To further characterize the A. oryzae hydrolysate, we analyzed the AA sequence of the whole peptide mixture. Various AA were detected at the first AA position, however, an increased number of Pro residues were observed at the second and third position of the A. oryzae hydrolysate. No strong signals were detected after the fourth AA position of the A. oryzae hydrolysate. These results suggest that the casein hydrolysate of A. oryzae, which expressed potent antihypertensive effects in spontaneously hypertensive rats, mainly contain short peptides of X-Pro and X-Pro-Pro sequences.

Amino Acid Sequence↗
PubMed2004

Effects of casein haplotypes on milk production traits in Italian Holstein and Brown Swiss cattle.

The objective of this study was to estimate the effects of different haplotypes of the casein genes on milk production traits in Italian dairy cattle. Traits of interest were yields of milk, fat, and protein, and percentages of fat and protein in milk. The data included 728 multiparous records from 347 Holsteins and 773 records from 298 Brown Swiss cows. Records were preadjusted for effects of age and parity, season of calving, and region, and expressed as deviations from herdmate averages. Twenty half-sib families were represented in each breed. Haplotype probabilities were estimated for each animal and phenotypes were regressed on these probabilities. Nine haplotypes were observed in Holsteins and 17 were identified among the Brown Swiss. For Holsteins, significant effects were observed for protein percentage, with some indication of an effect for fat percentage. For the Brown Swiss, effects of haplotypes were significant for milk yield and fat and protein percentages. Effects were strongest for protein percentage. Correlation coefficients of solutions across breeds tended to be strong and positive, indicating that the same haplotypes had similar estimated effects in the 2 breeds. Although the data were limited (<350 cows in each study), this latter result may suggest that genes in the casein complex itself are responsible for the effects observed, rather than loci that are physically linked on either side of the casein cluster.

Animals↗
PubMed1976

Two rapid and improved techniques for chromatographic fractionation of casein.

The major components of casein, alphas-, beta-, kappa-, and gamma-caseins, were chromatographically fractionated on diethylaminoethyl ion-exchange cellulose in stepwise elution with pH 8, .03 M glycine, or pH 7, .005 M phosphate buffers in the presence of 3.3 M urea and .1% 2-mercaptoethanol. Fractionation was at room temperature (around 25 C) in 4 to 4.5 h. The components showed a reasonable purity electrophoretically. These techniques can be used for quantitative estimation of casein composition.

Caseins↗
PubMed1976

Amino terminal sequence and location of phosphate groups of the major human casein.

The amino acid sequence of the first 28 residues of the major human casein was determined. This protein in multiphosphorylated forms (0 to 5 phosphorous per molecule) was compared to cow beta-casein which is similar in composition but phosphorylated at a constant level. After sequencing the phosphate-free human casein, phosphorylated seryl and threonyl residues were located in three of the other phosphorylated forms by examining the aqueous layer of the phenylthiohydantoin conversion step during automatic liquid phase sequencing. Phosphate groups on specific seryl/threonyl residues suggest a biosynthetic mechanism involving stepwise phosphorylation or dephosphorylation.

Amino Acid Sequence↗
PubMed1978

Secretion of casein in cultures of mouse mammary epithelial cells on floating collagen gels.

To study the effect of hormones on the secretion of casein, mammary epithelial cells were obtained from mid-pregnant mice and cultured on floating collagen gels in the presence of combinations of insulin, cortisol, and prolactin in serum-free culture medium. After labeling with phosphorus-32 labeled orthophosphate, the cells which had been cultured in the presence of all three hormones secreted hot-trichloroacetic acid precipitable radioactivity into the medium. The secreted materials were identified as three major mouse caseins by sodium dodecyl sulphate-urea polyacrylamide gel electrophoresis followed by autoradiography. The floating collagen gel culture method allows mouse mammary epithelial cells to differentiate and secrete all species of caseins in the presence of hormones. The present culture method and the phosphorus-32 labeling method will be applicable to the study of differentiation of mammary epithelial cells from a variety of mammalian species.

Animals↗
PubMed1980

Hydrolysis of beta-casein and peptides by intracellular neutral protease of Streptococcus diacetylactis.

The endopeptidase activity of mesophilic streptococci was characterized further by investigating the specificity of an intracellular endopeptidase from Streptococcus diacetylactis for beta-casein, derived peptides, and bradykinin. The inhibitory action of phosphoramidon as well as direct determinations of metal content showed this enzyme was a metalloprotein. Hydrolysis of native beta-casein was relatively low. Peptides obtained from the fraction soluble at pH 4.6 led to the demonstration that Pro186-Ile187 and Ala189-Phe190 were hydrolyzed by the enzyme. Two peptides derived from beta-casein by the action of chymosin were hydrolyzed efficiently: we observed hydrolysis of Lys176-Ala177, Lys169-Val170, and Pro206-Ile207. The Pro7-Phe8 bond of bradykinin was hydrolyzed rapidly, showing that this enzyme was efficient for the hydrolysis of prolyl peptide bonds. The protease was slightly less sensitive to phosphoramidon than was thermolysin. Metal analyses showed the enzyme contained 580 microgram of zinc and 4,760 microgram of calcium per gram protein. This protease is thus a true metalloenzyme (E.C.3.4.24.4), and its action may complete the hydrolysis initiated by chymosin remaining active in cheese curd by hydrolyzing peptides released by chymosin.

Animals↗

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