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PubMed1989

Intestinal apolipoprotein B-48 synthesis and lymphatic cholesterol transport are lower in swine fed high fat, high cholesterol diet with soy protein than with casein.

Effects of dietary proteins on intestinal lipoproteins were studied in 8 Yorkshire swine fed a high fat, high cholesterol diet with either casein or soy protein. After 5 weeks of feeding, the casein group exhibited moderately elevated levels of serum cholesterol (334 +/- 46 mg/dl). The soy protein group showed significantly less hypercholesterolemia as compared to the casein group (122 +/- 8 mg/dl). Swine were subjected to cannulation of mesenteric lymph duct under halothane anesthesia. A single dose of 250 microCi [14C]cholesterol and 10 mCi [3H]leucine was infused into the upper jejunum 2 h after one-fifth of daily food was given. The 3-h lymphatic transport of cholesterol in casein-fed swine was significantly higher than in those fed soy protein. Triglyceride transport values were similar in the 2 groups. The [3H]leucine incorporation study revealed that transport of apo B-48 bore a significant positive relationship to transport of cholesterol in both chylomicron and VLDL fractions of mesenteric lymph. A greater apo B-48 secretion with higher specific activity was probably responsible for the greater transport of cholesterol in chylomicrons in casein-fed than in soy protein-fed swine. Similarly, the transport of lymph VLDL cholesterol in swine fed casein or soy protein paralleled the amount of accompanying apo B-48. Dietary proteins probably influence the intestinal synthesis of apo B-48 which in turn affects cholesterol transport into the lymphatics.

Amino Acids↗
PubMed1989

Inhibition of casein synthesis by progestagens in vitro: modulation in relation to concentration of hormones that synergize with prolactin.

We studied the effect of progesterone and its agonist, R 5020, on casein and transferrin production in pregnant rabbit mammary gland explant culture and its modulation by hormones that synergize with prolactin. The glands were obtained from rabbits on days 12-14 of gestation. The progestins had no effect alone, but significantly inhibited ovine and porcine prolactin stimulation of casein synthesis in a dose dependent manner. There were no effects on transferrin content of the tissue, demonstrating a specific effect of progesterone on casein synthesis. In approx 15% of the cultures, prolactin stimulated casein production to very high levels and the progestins lost their inhibitory action. Progestins were also ineffective when the tissue was cultured with prolactin and unphysiologically high levels of insulin (5 mg/l) or cortisol (280 nmol/l), which stimulated casein synthesis to higher levels than prolactin alone. The concentration of cortisol used was 10 times higher than the serum levels seen in rabbits at the stage of gestation studied (approx 10 ng/ml) and corresponded to levels seen at the end of gestation, a period when the glands are secreting milk and progesterone serum levels have commenced to decrease. Thus, when the prolactin effect upon casein synthesis had been potentiated, whether spontaneously or through synergism with insulin or corticoids, progestins were unable to inhibit it, as is the case in lactating tissues. The results show that utilization of unphysiological levels of hormones in culture may distort the response of the tissue, masking responses that are clearly seen in vivo.

Animals↗
PubMed1985

Monoclonal antibodies to human casein.

Two monoclonal antibodies, LICR-LON-32.2 (32.2) and LICR-LON-14.1 (14.1), are described which react with human casein. 32.2 reacts with human beta-casein and 14.1 with human kappa-casein. 32.2 also reacts with rat band 2 casein and bovine beta-casein, but 14.1 appears to be specific for human kappa-casein. These monoclonal antibodies do not cross-react with other milk proteins.

Animals↗
PubMed1987

Purification of substrate proteins of casein kinases from the cytosol fraction of AH-66 hepatoma cells.

We have attempted to purify endogenous substrate proteins for casein kinases I and II from the cytosol of AH-66 hepatoma cells. Utilizing the fact that only a few substrates are concentrated in the fraction eluted from DEAE-cellulose between 0.3 and 0.6 M NaCl, two substrates were purified from this fraction by DEAE-cellulose chromatography, hydroxyapatite chromatography, and HPLC on a DEAE-5PW column. The purified substrate proteins had molecular masses of 30.5 kDa and 31 kDa. The 31-kDa protein substrate was markedly phosphorylated by casein kinase II, but only slightly by casein kinase I. The radioactive phosphate incorporated into 31-kDa substrate by casein kinase II was 0.2 mol/mol of the protein and phosphorylation occurred on both threonine and serine residues. The 30.5 kDa protein was only slightly phosphorylated by casein kinase II, but not at all by casein kinase I.

Amino Acids↗
PubMed1988

Identification of spinacine as the principal reaction product of gamma-casein with formaldehyde in cheese.

Formaldehyde is added to milk in the production of grana cheese as an antimicrobial agent. In order to study the fate of the formaldehyde, a grana cheese preparation was made using 14C-labelled formaldehyde. The 14C-activity in the cheese was found to be mainly associated with the caseins, but it was not uniformly distributed among the different fractions (alpha s, beta- and gamma-caseins). gamma-Casein, separated by electrophoresis, was the most reactive component showing the highest specific activity. In the gamma-casein fractions, 99% of 14C-activity was associated with the basic amino acids. The only radioactive reaction product present in the gamma-casein fraction was identified by HPTLC and by an amino acid analyser to be spinacine, a condensation product of formaldehyde and histidine. Using the same method, other unknown radioactive products, of much less relevance, were detected in the total casein hydrolysate.

Caseins↗
PubMed1985

Hormonal regulation of casein synthesis at the end of pregnancy.

Ovariectomy or ovariohysterectomy on day 18 of pregnancy augmented mammary beta-casein content 28 h later. Progesterone injected immediately and 12 h after ovariectomy showed a clear inhibitory effect on casein synthesis. Estrogen induced a significant increase in mammary beta-casein content when injected 12 h after surgery. Treatment with CB-154 to prevent prolactin release did not affect the increase of casein induced by ovariectomy. When CB-154 was injected to ovariohysterectomized pregnant rats, significant reduction of casein synthesis was obtained. According to these findings, rat placental lactogen in the absence of prolactin and progesterone induces beta-casein synthesis. Therefore prolactin, ovarian and placental hormones interplay at the end of pregnancy for full expression of the mammary gland genome.

Animals↗
PubMed1987

Binding and action of glucocorticoids and mineralocorticoids in rabbit mammary gland. Exclusive participation of glucocorticoid type II receptors for stimulation of casein synthesis.

In order to ascertain whether the effect of corticoids upon casein synthesis in pregnant rabbit mammary gland culture is due to interactions with classical glucocorticoid or type I (mineralocorticoid) receptors we have demonstrated the existence of both types of receptors in the tissue and have studied the effects of aldosterone and the specific glucocorticoid agonist RU 28362 upon casein synthesis in tissue culture. Both compounds significantly stimulated prolactin-induced casein synthesis. On dose-response studies RU 28362 proved to be as active as dexamethasone, cortisol was active at intermediate concentrations and aldosterone was the least active. The three glucocorticoids were able to stimulate DNA synthesis in the tissue, but aldosterone had no effect. Finally, RU 486, a potent glucocorticoid antagonist, blocked the action of aldosterone and the other corticoids upon casein synthesis, whereas spironolactone, a mineralocorticoid antagonist, was unable to do so. These results demonstrate that the stimulatory effect of corticoids upon casein synthesis in pregnant rabbit mammary tissue culture is mediated through classical (type II) glucocorticoid receptors. Transferrin accumulation in the tissue was not modified by any treatment, indicating that the action of the steroids was specific for casein, and not a general stimulation of protein synthesis.

Aldosterone↗
PubMed1986

Degradation of newly-synthesised casein in mammary explants from pregnant and lactating goats.

Casein degradation was measured by a pulse-chase method in explants from freshly-prepared from goat mammary tissue. An initial increase in L-[5-3H]proline radioactivity incorporated in casein during the chase period was followed in some conditions by a decrease resulting from intracellular degradation of the major casein polypeptides. Differences in the proportion of casein degraded in explants cultured with or without prolactin suggested that the process was under hormonal control. Greater degradation of casein by explants obtained in late pregnancy and early lactation suggested that the process may affect net casein production in vivo.

Animals↗
PubMed1993

The isolation and properties of whole casein: some implications for comparative studies.

1. Problems in the isolation of whole casein from bovine milk are considered. A summary is given of our experiences in its isolation. 2. The physical characteristics, sedimentation velocity, heterogeneity, absorptivity, nitrogen, phosphorus and carbohydrate contents of whole casein prepared from normal and sub-clinical mastitic milk samples by a variety of methods are compared. The methods are acid precipitation, high-speed centrifugation, with and without added calcium (II), and ammonium sulphate precipitation. 3. A description is given of the low temperature ammonium sulphate procedure preferred for the isolation of whole casein, especially when it is to be used for subsequent fractionation for conformation and micelle studies. 4. The question of the use of bovine casein as a paradigm for the caseins of other mammalian species and the need for further studies of the physical, chemical and biological properties of the caseins are discussed.

Absorption↗
PubMed1984

Identification of bacterial clones encoding bovine caseins by direct immunological screening of the cDNA library.

A sensitive immunoassay was used to identify recombinant plasmids carrying cDNA fragments of bovine caseins in the cDNA library from bovine mammary gland mRNA. Colonies grown on nitrocellulose filters were lysed in situ and proteins from the lysates were blotted onto CNBr-activated cellulose filter paper. Antigens covalently bound to CNBr-activated paper or bound to nitrocellulose filters were detected by reaction with antiserum to caseins, followed by 125I-labelled Staphylococcus aureus protein A and autoradiography. Six clones were found positive among 5400 of the cDNA library: 3-A1, 3-B2, 3-B5, 3-H7, 2-A5 and 2-C9. The molecular weights of chimeric pre-beta-lactamase: casein proteins synthesized in Escherichia coli were estimated by immunoblotting. Colony hybridization and nucleotide sequence analysis showed that clone 3-B5 contained a cDNA fragment of bovine chi-casein, clone 3-H7 contained a cDNA fragment of beta-casein, while clones 2-A5 and 2-C9 carried cDNA fragments of alpha s1-casein.

Animals↗
PubMed1993

The activated mammary gland specific nuclear factor (MGF) enhances in vitro transcription of the beta-casein gene promoter.

The hormonal induction of the beta-casein gene in mammary epithelial cells is dependent on the action of peptide and steroid hormones. Epidermal growth factor, insulin, glucocorticoids and prolactin act in a sequential manner to regulate the transcription of the gene. We have studied the hormonal requirements as well as the nuclear proteins which are involved in the induction process. In vitro transcription in cell free nuclear extracts has been used to demonstrate the central role of the mammary gland specific nuclear factor, MGF, in the mediation of the hormonal signals to the transcription machinery. A gene construct comprising 344 nucleotides of wild type beta-casein promoter sequence and a G-free cassette of 220 nucleotides was used to test the activity of nuclear extracts in the in vitro transcription experiments. A construct in which the proximal MGF binding site in the beta-casein promoter region has been inactivated by mutation and a construct regulated by the adenovirus major late promoter served as controls. Nuclear extracts were prepared from Sf insect cells, HeLa cells and mammary epithelial cells of lactating rats. Strong transcription of the wild type beta-casein promoter construct was observed in the mammary cell extract, weak transcription in the extracts of Sf insect cells and the HeLa cells. The mutation of the MGF binding site drastically reduced the in vitro transcription in the mammary gland cell extract. Beta-casein promoter activity was also compared in nuclear extracts from uninduced and lactogenic hormone induced HC11 mammary epithelial cells. Extracts from induced cells are more efficient in the support of beta-casein gene transcription.

Animals↗
PubMed1995

The effects of various kinase and phosphatase inhibitors on the transmission of the prolactin and extracellular matrix signals to rabbit alpha S1-casein and transferrin genes.

In all species, milk protein genes are specifically expressed in the mammary gland under the control of lactogenic hormones and extracellular matrix. In rabbit, casein gene expression is induced by prolactin alone and this induction is amplified by extracellular matrix. Transferrin gene expression is induced by extracellular matrix in the absence of hormones. The transduction mechanisms of prolactin and extracellular matrix to milk protein genes is only partly known. The present study has been undertaken to determine if protein kinases and phosphatases are involved in these mechanisms. Rabbit primary mammary cells were cultured in three different conditions (i) directly on floating collagen I, (ii) on plastic after a trypsinization to remove endogenous extracellular matrix, and (iii) on floating collagen I after a trypsinization to restore a functional extracellular matrix. In these culture conditions, prolactin and several protein kinase and phosphatase inhibitors were added to the medium. The expression of alpha S1-casein and transferrin genes was evaluated using Northern blotting analysis. In cells cultured directly on collagen I, staurosporine, quercetin and 6-dimethylaminopurine strongly inhibited prolactin action of alpha S1-casein gene whereas herbimycin A was only partly inhibitory. An erbstatin analogue, tyrosine phosphate, 1(5 isoquinolylsulphonyl) 2-methylpiperazine and GF 109 203 X did not alter prolactin action. The inhibitors which inhibited prolactin action when cells were directly cultured on collagen I were also those which prevented the induction of alpha S1-casein gene expression when cells were cultured on plastic in the absence of extracellular matrix. The induction of transferrin gene by the extracellular matrix was inhibited slightly by quercetin. Okadaic acid, phenylarsine oxide and sodium pervanadate which inhibit Ser/Thr and Tyr phosphatase inhibitors were unable to mimic prolactin action on alpha S1-casein gene expression. On the contrary, these inhibitors prevented prolactin action. These data suggest that a cascade including protein kinases and phosphatases for Ser/Thr and Tyr phosphate is involved in the transduction of the prolactin message from its receptor to casein genes. The signal delivered to the mammary cells by the extracellular matrix is quite different, possibly involving another cascade of protein kinases.

Animals↗
PubMed2006

Isolation and some effects of functional, low-phenylalanine kappa-casein expressed in the milk of transgenic rabbits.

Patients suffering certain metabolic diseases (e.g. phenylketonuria) need a low-phenylalanine diet throughout their lives. Transgenic rabbits were created to express low-phenylalanine kappa-casein in their milk. The aim was to demonstrate for the first time the feasibility of producing a modified milk protein in addition to normal milk proteins. A gene construct containing the coding region of the rabbit kappa-casein gene was modified by site-specific oligonucleotide directed mutagenesis. Four of the five phenylalanine amino acids present in the mature protein were mutated and the gene construct was used to create two transgenic rabbit lines. The transgenic rabbits produced the recombinant kappa-casein at a high level in their milk causing a reduction in the average size of the casein micelles. The low-phenylalanine kappa-casein was digestible with chymosin and it was separated from its native counterpart and from the other milk proteins by a one-step HPLC method on a reversed-phase column. In the future, low-phenylalanine casein produced in transgenic animals could be used as dietary replacements to meet the special requirements of certain consumer groups.

Animals↗
PubMed2007

Soy compared to casein meal replacement shakes with energy-restricted diets for obese women: randomized controlled trial.

Recent studies suggest that obese individuals lose weight more rapidly and lose more total weight with soy protein than with animal protein as a major diet component. The purpose of the present study was to evaluate the weight-loss efficacy and changes in body composition, waist circumference, blood pressure, and levels of plasma glucose, insulin, serum lipids, C-reactive protein, and homocysteine from consumption of either 3 soy shakes or 3 casein shakes daily as part of a 16-week, energy-restricted diet for obese women. Forty-three women with body mass index values of 30 to 40 kg/m(2) were randomized to intensive dietary interventions using either casein (n = 21) or soy (n = 22) shakes. Subjects were instructed to consume 3 shakes, 1 prepackaged entrée, and 5 servings of fruits or vegetables daily to achieve an energy intake of 4.5 to 5.0 MJ/d. Subjects attended classes weekly or biweekly. Weight, body fat, lipid, and glucose measurements were obtained at baseline and at 8 and 16 weeks. For both groups combined, subjects lost 8.1% of initial body weight (7.7 kg) at 8 weeks and 13.4% (12.7 kg) at 16 weeks. Weight loss from baseline did not differ significantly by group and, for completing subjects, was 14.0% +/- 1.2% (mean +/- SE) for casein and 12.8% +/- 1.4% for soy. With the intention-to-treat analysis, weight losses at 16 weeks were 12.5% +/- 1.4% for casein and 11.3% +/- 1.2% for soy. Body fat losses were 23.7% +/- 2.0% for casein and 21.8% +/- 2.4% for soy and did not differ significantly. Both study groups lost significant amounts of weight with a highly structured behavioral program incorporating 4 meal replacements and vegetables and fruits. Differences in weight loss and body composition changes between casein and soy treatments were not significant.

Adipose Tissue↗
PubMed2002

Effects of structural rearrangements on the rheology of rennet-induced casein particle gels.

During ageing of casein or skim milk gels, structural changes take place that affect gel parameters, such as pore size and storage modulus. These changes can be explained in terms of rearrangements of the gel network at various length scales. In this paper, rheological experiments on rennet-induced casein gels and a general model on rearrangements are presented. The results of experiments (e.g. microscopy, permeametry) and computer simulations, the model, and recent literature on casein gels and other types of particle gels are compared to each other. Experiments presented include measurements of storage and loss moduli and maximum linear strain of the casein gels. Parameters varied were pH (5.3 and 6.65) and temperature (25 and 30 degrees C). In addition, the casein volume fraction (5-9 vol.%) was varied, which enables application of fractal scaling models. For rennet-induced casein gels, it is demonstrated that at the lower pH, all types of rearrangements proceed significantly faster. The rearrangements include: an increase in the size of compact building blocks; partial disappearance of fractal structure; and the formation of straightened strands, some of which eventually break. All of these rearrangements seem to be a consequence of particle fusion. There are indications of universality of the relation between particle fusion and gel syneresis for gels composed of viscoelastic particles.

Animals↗
PubMed1988

Phosphorylation of protein B-50 (GAP-43) from adult rat brain cortex by casein kinase II.

The phosphoprotein B-50 (GAP-43) was purified from adult rat brain cortex and phosphorylated by casein kinase II. Phosphorylation of B-50 by casein kinase II approached 1.2 mol phosphate/mol B-50. The apparent Km of casein kinase II for B-50 was 4 microM with an apparent Vmax of 13 nmol.min-1.mg-1. A tryptic phosphopeptide map on reversed phase HPLC and phosphoamino acid analysis of [32P]B-50 showed that casein kinase II phosphorylated in serine residue(s) which were located in a single tryptic peptide. Phosphorylation of B-50 by casein kinase II was inhibited more than 90% by 5 micrograms heparin/ml or 2.4 mM peptide substrate specific for casein kinase II (RRREEETEEE). The initial phosphorylation rate was increased about 2-fold by 1 mM spermine.

Animals↗
PubMed2000

Post-translational phosphorylation affects the IgE binding capacity of caseins.

IgE response specific to those molecular regions of casein that contain a major phosphorylation site was analyzed using native and modified caseins and derived peptides. This study included (i) the naturally occurring common variants A1 and A from beta- and alphas2-caseins, respectively, which were purified in the native form and then dephosphorylated, (ii) a purified rare variant D of alphas2-casein which lacks one major phosphorylation site, and (iii) the native and dephosphorylated tryptic fragment f(1-25) from beta-casein. Direct and indirect ELISA using sera from patients allergic to milk showed that the IgE response to caseins is affected by modifying or eliminating the major phosphorylation site.

Binding Sites↗
PubMed1997

A novel, calcium-inhibitable casein kinase in Paramecium cells.

This is the first identification of a Ca2+-inhibitable casein kinase (CPK) which we have isolated from the 100000 x g supernatant of Paramecium cell homogenates. The 1000-fold enriched CPK activity depends on millimolar Mg2+ and is inhibited by low concentrations of heparin or by > or = 100 microM Ca2+. Enzyme activity is stimulated by polylysine or polyarginine with either casein or with specific casein kinase-2 (CK-2) peptide substrates (RRRDDDSDDD and RREEETEEE). The enzymic properties are similar with GTP instead of ATP. CPK does not undergo autophosphorylation. In gel kinase assays, enzyme activity is associated with a 36 kDa band. Calmodulin as another characteristic substrate for mammalian CK-2 has not been phosphorylated by this protein kinase. Besides casein, CPK phosphorylates in vitro the catalytic subunit of bovine brain calcineurin (CaN), a typical substrate of type 1 mammalian casein kinase (CK-1) in vitro. Again this phosphorylation is significantly reduced by Ca2+. Thus, CPK combines aspects of different casein kinases, but it is clearly different from any type known by its Ca2+ inhibition. Since CPK also phosphorylates the exocytosis-sensitive phosphoprotein, PP63, in Paramecium, which is known to be dephosphorylated by CaN, an antagonistic Ca2+-effect during phosphorylation/dephosphorylation cycles may be relevant for exocytosis regulation.

Amino Acid Sequence↗