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PubMed1983

Phosphorylation and inactivation of rat liver glycogen synthase by cAMP-dependent protein kinase and cAMP-independent synthase (casein) kinase-1.

Phosphorylation of liver glycogen synthase by cAMP-dependent protein kinase (A-kinase) results in the incorporation of approximately 0.7 to 1.0 mol of PO4/subunit. Analyses of the tryptic peptides by isoelectric focusing and peptide mapping reveal the presence of a single 32P-labeled peptide. This extent of phosphorylation does not result in a significant reduction of the synthase activity ratio. Phosphorylation of the liver synthase by cAMP-independent synthase (casein) kinase-1 results in the incorporation of 1.6 to 2.2 mol of PO4/subunit. Although at least 4 tryptic peptides have been found to be labeled with 32P, no significant reduction of the synthase activity ratio was observed. Under the same assay conditions, the muscle synthase is effectively inactivated by either kinase alone or in combination. Inactivation of liver synthase can be achieved after phosphorylation by A-kinase and followed by synthase (casein) kinase-1. However, the inactivation becomes less effective if the order of the addition of these two kinases is reversed. Under the latter assay condition, the phosphate incorporation is less than additive in the presence of both kinases. Prior phosphorylation of the synthase by A-kinase transforms the synthase to become a better substrate for synthase (casein) kinase-1 as evidenced by a 3- to 5-fold increase in the rate of phosphorylation. This increased rate of phosphorylation of the synthase by synthase (casein) kinase-1 results from the rapid phosphorylation of a site neighboring to that previously phosphorylated by A-kinase.

Animals↗

PubMed1983

Description of a protein kinase derived from insulin-treated 3T3-L1 cells that catalyzes the phosphorylation of ribosomal protein S6 and casein.

Particulate preparations from insulin-treated 3T3-L1 cells retain the enhanced ability to incorporate 32P from [gamma-32P]ATP into ribosomal protein S6 (Smith, C. J., Rubin, C. S., and Rosen, O. M. (1980) Proc. Natl. Acad. Sci. U. S. A. 77, 2641-2645). A cyclic AMP-independent protein kinase that phosphorylates S6 and casein and that may be involved in the increase in S6 phosphorylation produced by insulin has been isolated based upon the observation that there is 1.5-3.0-fold higher activity in particulate preparations derived from insulin-treated cells than there is in comparable preparations from control cells. The enzyme activity was purified 2071-fold by KCl extraction, phosphocellulose chromatography, and gel filtration. The S6 phosphorylating activity was also characterized by its behavior on casein-Sepharose and DEAE-cellulose chromatography and its sedimentation in glycerol gradients. None of these procedures resolved the S6 and casein kinase activities. Some of the properties of this kinase, including a molecular weight of about 35,000, inhibition by F- or phosphate, chromatography on DEAE-cellulose and phosphocellulose, and insensitivity to inhibition by GTP, are similar to those of a previously described enzyme, casein kinase I (Dahmus, M. E. (1981) J. Biol. Chem. 256, 3319-3325; Hathaway, G. M., and Traugh, J. A. (1979) J. Biol. Chem. 254, 762-768).

Adipose Tissue↗

PubMed1980

Inhibition of casein kinase II by heparin.

Casein kinase II, a cyclic nucleotide-independent protein kinase from rabbit reticulocytes, was shown to be inhibited by heparin. Heparin specifically inhibited the enzyme and had no effect on other protein kinases, including casein kinase I, the type I and II cAMP-dependent protein kinases, protease-activated kinase I, and the hemin-controlled repressor. Heparan sulfate was found to be 40-fold less effective than heparin towards casein kinase II; other acid mucopolysaccharides had little or no effect on the enzymatic activity. Steady state studies revealed that heparin acted as a competitive inhibitor with respect to the substrate, casein. A value of 20 ng/ml or about 1.4 nM was obtained for the apparent Ki. The inhibition was not reversed by ATP and varying the ATP and heparin concentrations in the assay only altered the maximum velocity.

Animals↗

PubMed1984

Similarities in structure and function of calf thymus and Drosophila casein kinase II.

Both calf and Drosophila contain a type II casein kinase with similar molecular structure and catalytic activity. Purified calf thymus casein kinase II is composed of three subunits of Mr = 44,000 (alpha), 40,000 (alpha'), and 26,000 (beta) (Dahmus, M.E. (1981) J. Biol. Chem. 256, 3319-3325), whereas the Drosophila enzyme is composed of two subunits of Mr = 36,700 (alpha) and 28,200 (beta) (Glover, C. V. C., Shelton, E. R., and Brutlag, D. L. (1983) J. Biol. Chem. 258, 3258-3265). The native form of the enzyme is an alpha 2 beta 2 tetramer. Polyclonal antibodies prepared against each enzyme react with both the alpha and beta subunits of the homologous enzyme and cross-react with both subunits of the heterologous enzyme. Reaction of polyclonal antibodies with proteins resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis establishes that no significant difference in subunit molecular weight exists between the purified enzymes and the enzyme present in initial cell extracts. Each antibody effectively inhibits the in vitro activity of the homologous enzyme and causes a slight inhibition in the activity of the heterologous enzyme. Peptide maps derived from purified subunits indicate that the alpha and beta subunits are unique and that there is extensive primary sequence homology between the corresponding subunits of the calf and Drosophila enzyme. Casein kinase II from both sources phosphorylates the same subunits of calf thymus RNA polymerase II and an identical set of proteins in a complex mixture of acid-soluble proteins from Drosophila tissue culture cells. The striking similarity in molecular structure and catalytic activity between the calf and Drosophila enzyme suggests that casein kinase II has been highly conserved in evolution.

Animals↗

PubMed1983

Correlation between nuclear glucocorticoid receptor levels and casein gene expression in murine mammary gland in vitro.

The relationship between nuclear binding of glucocorticoid-receptor complex and casein gene expression was studied in organ culture of the whole mammary gland of the mouse. Pyridoxal 5'-phosphate was used as a modulatory agent for measuring nuclear binding of the receptor complex. Addition of 2 mM and 5mM pyridoxal-5'-P in the medium (Waymouth's MB752/1) resulted in 4- and 12-fold increase of its concentration in the glands incubated with insulin, prolactin, and hydrocortisone. Pyridoxal-5'-P also caused a 52% and 92% inhibition of nuclear binding of [3H]dexamethasone in the glands at 2 mM and 5 mM concentration in the presence of the same hormones in the medium. Corresponding to the reduced nuclear binding of the receptor complex casein mRNA levels, measured by a specific cDNA probe was reduced 86% and over 90% in the glands exposed to 2 mM and 5 mM pyridoxal-5'-P, respectively, in presence of insulin, prolactin, and hydrocortisone in the medium. Withdrawal of pyridoxal-5'-P from the medium restored nuclear binding of the receptor complex near the level of control glands incubated only with the hormones. mRNA casein levels also increased in the gland in the pyridoxal-5'-P-free medium containing the same hormones. This indicates that pyridoxal-5'-P does not alter the specific hormone responsiveness of the mammary cells and its action mediated at the level of the glucocorticoid receptor can influence hormone-inducible expression of the casein genes. Thus, glucocorticoid plays a major role in the multiple hormone regulation of the milk protein gene(s). The findings also suggest that the breast tissue concentration of the vitamin B6 derivative may influence the physiology of lactation in nursing mothers.

Animals↗

PubMed1978

Differential regulation of alpha-lactalbumin and casein messenger RNA's in mammary tissue.

Rat caseins were characterized with respect to moleculare weight and carbohydrate and amino acid content. Messenger RNA was extracted from rat mammary glands at 5, 10, 15, and 20 days of pregnancy and at 2, 8, and 15 days of lactation and translated in a wheat germ cell-free system. Nascent [3H]casein and alpha-[3H]actalbumin were precipitated separately with specific antibodies and identified by their mobilities on sodium dodecyl sulfate:acrylamide gels and by competition with unlabeled casein and alpha-lactalbumin, respectively. Casein messenger rose continuously from Day 5 of pregnancy to Day 15 of lactation. In contrast, alpha-lactalbumin messenger RNA levels remained low during pregnancy but rose markedly during lactation.

Animals↗

PubMed1982

Kinetics of Phosphorylation of eIF-2 by the hemin-controlled repressor and casein kinase II. Inhibition by hemin and 2,3-diphosphoglyceric acid.

The kinetics of phosphorylation of eukaryotic initiation factor 2 (eIF-2) by two cyclic nucleotide-independent protein kinases from rabbit reticulocytes have been studied. The hemin-controlled repressor (HCR) and casein kinase II phosphorylate the alpha and beta subunits of eIF-2, respectively. The apparent Km for eIF-2 with HCR and casein kinase II was determined to be in the range of 0.5-1.0 microM. Using fully dephosphorylated eIF-2, it was possible to show that the phosphorylation state of the beta subunit did not affect the apparent Km of either HCR or casein kinase II for eIF-2. The effects of two inhibitory compounds, hemin and 2,3-diphosphoglyceric acid (2,3-DPG), were studied also. Hemin acted as a noncompetitive inhibitor of HCR with respect to eIF-2 with an apparent Ki of 3 microM, while inhibition of casein kinase II by 2,3-DPG was competitive with respect to eIF-2. The apparent inhibitory constant was determined to be 1 mM, a concentration within the physiological range of 2,3-DPG in red blood cells. From the kinetic values obtained with hemin and 2,3-DPG, it appears that these compounds could directly regulate the respective protein kinases in vivo.

2,3-Diphosphoglycerate↗

PubMed1993

L-29, a soluble lactose-binding lectin, is phosphorylated on serine 6 and serine 12 in vivo and by casein kinase I.

L-29, a mammalian soluble lactose-binding lectin, was previously shown to be phosphorylated in confluent 3T3 fibroblasts (Cowles, E. A., Agrwal, N., Anderson, R. L., and Wang, J. L. (1990) J. Biol. Chem. 265, 17706-17712), which contain a small amount of this protein. We have determined the site of phosphorylation on L-29, taking advantage of the abundance of L-29 (about 1% of total soluble cell protein) in confluent polarized Madin-Darby canine kidney (MDCK) cells. Approximately 15-20% of the L-29 is phosphorylated in these cells. Phosphoamino acid analysis showed phosphate incorporation only at serine. Analysis of chymotryptic and endoproteinase Asp-N-generated NH2-terminal fragments by Edman degradation showed that 90% of the phosphate was at Ser6 and 10% at Ser12. The sequence surrounding Ser6, which is conserved in all known L-29 sequences, indicated that this serine might be phosphorylated by casein kinase I or casein kinase II. Reaction of human recombinant L-29 with [gamma-32P]ATP and each of these casein kinases showed that only casein kinase I catalyzed significant incorporation of 32P into L-29; and, as with the L-29 from the MDCK cell extracts, most of the phosphate was incorporated at Ser6 and a small amount was incorporated at Ser12.

Amino Acid Sequence↗

PubMed1977

Casein production by human breast cancer.

Casein was measured in the sera of breast cancer patients, in breast cancer tumors, and in breast cancer cells in long-term tissue culture using a sensitive and specific radioimmunoassay. Levels present in breast cancer sera were not elevated above control values. Eight of forty-seven (17%) of the tumor samples tested were positive for casein, the highest level representing 0.003% of the soluble protein. When seven human breast cancer cell lines were assayed for casein, the results were uniformly negative even under conditions of stimulation by lactogenic hormones. In addition, direct immunoprecipitation of labeled cellular protein supported the negative result of the radioimmunoassay. Thus it appears that casein production is not a common characteristic of most human breast cancers.

Breast Neoplasms↗

PubMedDate not supplied

Inhibition of small intestinal motility by casein: a role of beta casomorphins?

Several aspects on the effect of nutrients on small intestinal motility are not completely understood. We have analyzed changes of motor activity of the canine small bowel following intragastric administration of casein and soy protein. Studies were performed by intraluminal manometry with external transducers and multiple infused catheters with closely spaced registrating sites. Casein was followed by a statistically significant decrease of amplitude and frequency of small intestinal contractions, compared to soy protein. Pretreatment with naloxone suppressed the inhibitory effect of casein, suggesting that stimulation of opioid receptors by beta casomorphins, a product of digestion of casein, might be involved in the motility changes observed.

Animals↗

PubMed1995

[Effect of casein on D-xylose absorption assessed by H2 breath test].

UNLABELLED: Different experimental studies suggest that the presence of food in the alimentary tract, promote small intestinal absorption. The mechanisms involved are not completely understood and might be related to motility changes or to humoral factors. Since studies have shown a decrease of small bowel motility after casein administration, the aim was to analyze the effect of this protein on small intestinal absorption and orocecal transit time. The hydrogen breath test was used to estimate d-xylose absorption. H2 production is dependent on the amount of this carbohydrate reaching the colon, and therefore inversely proportional to d-xylose absorption. Six normal volunteers ingested 25 g d-xylose and 25 g d-xylose + 30 g casein, and alveolar breath samples were obtained at 15 min intervals. RESULTS: by adding casein to d-xylose solution a statistically significant decrease of maximal H2 concentration was observed from a mean of 40 +/- 11 ppm to a mean of 26 +/- 8 ppm. Similarly the area under the curve (which reflects the amount of xylose that was not absorbed) was also significantly decreased from a mean of 3281 +/- 1399 ppm to mean of 1394 +/- 700 ppm of H2. The orocecal transit time was significantly prolonged from 85.5 +/- 40 min to 112 +/- 38 min. Our results suggest that casein increases d-xylose absorption in normal subjects and that this effect might be related to a slower transit time.

Adolescent↗

PubMed1995

Effects of diet enrichment with glucose and casein on blood cortisol concentration of calves in early postnatal period.

The studies were carried out on 30 calves from the 4th to the 25th day of life, divided in three groups; control, glucose and casein. The glucose group was fed a diet containing 25% more glucose than the control. The increased dietary glucose supply decreased cortisol concentration in blood serum. The casein group was fed a diet containing 25% more protein-casein-than the control. The increased dietary casein supply increased the blood serum cortisol concentration. The changes discussed were observed not only during the period of diet application, but also a few days following the termination of the diet.

Aging↗

PubMedDate not supplied

Whey and casein specific IgE and the cow's milk challenge test for atopic children.

We studied 30 atopic children who suspected of milk allergy by past history (age ranging from 1 yr 4 mo to 9 yr 6 mo, mean age: 5.03 yr.) diagnosed as having asthma, atopic dermatitis and/or allergic rhinitis. These 30 atopic children had been screened from the patients at our outpatient clinic by the Pharmacia CAP system RAST FEIA. All of them showed the presence of at least Class II (greater than 0.7 ku/l) IgE specific to proteins in cow's milk. Further analysis found IgE specific to alpha-lactoalbumin (alpha-LA) elevated in 1 patient (3.3%), 1 patient (3.3%) to beta-lactoglobulin (beta-LG), 4 patients (13.3%) to alpha-LA and beta-LG, 5 patients (16.7%) to casein, 8 patients (26.7%) to casein and alpha-LA, 11 patients (36.7%) to casein, alpha-LA and beta-LG. After 3 weeks' cow-milk-free diet, the patient's milk challenge test was performed at our outpatient clinic. According to the test result, none of these 30 atopic children showed clinical evidence of significant allergic reaction to cow's milk in the skin, the gastrointestinal tract or the respiratory tract either within two hours after the challenge test or within 3 days after they went home. We therefore conclude that: (1) No single major allergen is apparent in cow's milk: casein, alpha-LA and beta-LG all show a high proportion of positive reaction. (2) Many atopic children fully tolerate cow's milk, although they have high titer of IgE antibodies specific to cow's milk. The RAST test is only the first step to screen patients with suspected IgE-mediated allergies. To make sure, any positive reaction must be confirmed by the "golden standard" for diagnosis, i.e., the double-blind placebo-controlled food challenge.

Animals↗

PubMedDate not supplied

Rapid separation and quantification of major caseins and whey proteins of bovine milk by capillary electrophoresis.

A rapid capillary zone electrophoresis (CZE) method was established for separating and quantifying major casein and whey proteins in milk. Optimum sample preparation and electrophoretic conditions in a coated capillary maintained at 40 degrees C allowed accurate and reproducible quantification of milk proteins in a single analysis. Sample and run buffer allowed caseins to be maintained in solution by using a combination of urea and a nonionic detergent in phosphate buffer at pH 2.5. Quantitative CZE protein data were derived by calculating percentages and concentrations (mg/mL) of alpha-casein, beta-casein, alpha-lactalbumin, and beta-lactoglobulin. Calibration curves followed linear relationships with highly significant (p < 0.1) correlation coefficients. Relative standard deviations of less than 0.82 (%) for migration times and 2.18 (%) for percent protein indicated that the technique was reproducible. Electrophoretic protein profiles of fresh bovine milk and rehydrated dry milk showed marked quantitative differences in whey protein concentrations. Whey protein represented 12.37 +/- 0.07% beta-lactoglobulin and 3.05 +/- 0.08% alpha-lactalbumin of total protein in typical fresh milk, while only 1.90 +/- 0.16% beta-lactoglobulin and 0.86 +/- 0.04% alpha-lactalbumin of total protein were detected in a commercial rehydrated milk powder. By quantifying these differences, the established technique may allow the detection of substitution of fresh milk with rehydrated milk powder. The accuracy and reproducibility of the technique permitted the quantitation of individual protein concentrations in milk samples, which agreed with ranges reported in the literature. CZE may be well suited for routine use by dairies and regulatory agencies, since it allows the determination of milk proteins in less than 60 min.

Animals↗

PubMed2004

Kinetics of rennet casein gelation at different cooling rates.

A mathematical model was developed to quantitatively analyze the rheological data of rennet casein gelation at different cooling rates. Kinetic parameters were estimated and correlated with the microstructure development of the protein network. The kinetic model identified structure development upon cooling to be first order, and the network forming energies were estimated for four protein concentrations cooled at four rates. A lower energy for network formation was observed for a slower cooling rate and a higher protein concentration. This observation resulted from the availability of more flocs at a slower cooling rate and a higher casein concentration, simplifying floc cross-linking. By analyzing the kinetics during the aging process of casein gels, no difference in the reaction mechanism was observed. This study illustrated that structure formation resulted from the addition of flocs into the protein network: not all flocs were part of the network at a defined gel point. The incubation period following cooling integrated idle flocs into the network, thereby strengthening the gel. By understanding the gelation mechanism during cooling of rennet casein gels, the structure and thus quality of dairy products, such as processed cheese, may be better controlled.

Journal Article↗

PubMed2003

Lipid oxidation in corn oil-in-water emulsions stabilized by casein, whey protein isolate, and soy protein isolate.

Proteins can be used to produce cationic oil-in-water emulsion droplets at pH 3.0 that have high oxidative stability. This research investigated differences in the physical properties and oxidative stability of corn oil-in-water emulsions stabilized by casein, whey protein isolate (WPI), or soy protein isolate (SPI) at pH 3.0. Emulsions were prepared with 5% corn oil and 0.2-1.5% protein. Physically stable, monomodal emulsions were prepared with 1.5% casein, 1.0 or 1.5% SPI, and > or =0.5% WPI. The oxidative stability of the different protein-stabilized emulsions was in the order of casein > WPI > SPI as determined by monitoring both lipid hydroperoxide and headspace hexanal formation. The degree of positive charge on the protein-stabilized emulsion droplets was not the only factor involved in the inhibition of lipid oxidation because the charge of the emulsion droplets (WPI > casein > or = SPI) did not parallel oxidative stability. Other potential reasons for differences in oxidative stability of the protein-stabilized emulsions include differences in interfacial film thickness, protein chelating properties, and differences in free radical scavenging amino acids. This research shows that differences can be seen in the oxidative stability of protein-stabilized emulsions; however, further research is needed to determine the mechanisms for these differences.

Chemical Phenomena↗

PubMed1994

Characterization of a proline-directed casein kinase from bovine brain.

A messenger-independent ser/thr casein kinase, p45 casein kinase (p45 CK), was purified to homogeneity from bovine brain. The enzyme is specific for ATP with a Km value of 3.50 microM, one of the lowest values identified for protein kinases, p45 casein kinase is active over broad NaCl concentrations from 30 to 300 mM. The enzyme activity is inhibited by polylysine, spermine, transition metal ions, ADP, and AMP. The kinase completely lost its activity in the presence of 1 mM p-chloromercuric benzoate in a reaction that is reversed by 1 mM dithiothreitol. The enzyme prefers serine over threonine in its substrate bradykinin, the Vmax/Km ratio for the serine peptide (RPPGFSPFR) being 7.5-fold higher than for the threonine analog (RPPGFTPFR). Assays, performed by utilizing synthetic peptides, suggest that p45 CK prefers serine/threonine residues with a proline residue immediately carboxy-terminal to the site of phosphorylation. Distinction between p45 CK and other protein kinases found to contain a proline residue within their substrate recognition sites can be made based on phosphorylation site specificity and chromatographic and biochemical behavior. It is concluded that p45 CK is a proline-directed protein kinase recognizing the sequence X-Ser/Thr-Pro-X or Ser/Thr-Pro-X.

Adenosine Triphosphate↗

PubMed1989

Involvement of protein kinase A and casein kinase II in the in vivo protein kinase activities in prophase arrested Xenopus oocytes.

In vivo beta casein phosphorylation was analysed in Xenopus full-grown oocytes arrested in the prophase of the meiotic cell division. The phosphorylation was inhibited by the protein kinase inhibitor (PKI) and also by heparin (3 micrograms/ml; final concentration). beta casein phosphorylation was increased by spermine (2 mM). Therefore, protein kinase A and casein kinase II are both active in vivo in full-grown oocytes and may be involved in the prophase arrest of meiotic cell division.

Animals↗