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PubMed1988

Phosphorylation of hepatic insulin receptor by casein kinase 2.

Casein kinase 2 was able to phosphorylate the beta-subunit of hepatic insulin receptor in the presence of either ATP or GTP. Phosphorylation by casein kinase 2 was observed even in the absence of insulin, was inhibited by low heparin concentrations, and led to the incorporation of phosphate on serine and threonine residues. Casein kinase 2 phosphorylation of insulin receptor partially decreased its tyrosine kinase activity.

Adenosine Triphosphate↗
PubMed1989

Phosphorylation of P1, a high mobility group-like protein, catalyzed by casein kinase II, protein kinase C, cyclic AMP-dependent protein kinase and calcium/calmodulin-dependent protein kinase II.

P1, a high mobility group-like nuclear protein, phosphorylated by casein kinase II on multiple sites in situ, has been found to be phosphorylated in vitro by protein kinase C, cyclic AMP-dependent protein kinase and calcium/calmodulin-dependent protein kinase II on multiple and mostly distinct thermolytic peptides. All these enzymes phosphorylated predominantly serine residues, with casein kinase II and protein kinase C also labeling threonine residues. Both casein kinase II and second messenger-regulated protein kinases, particularly protein kinase C, might therefore be involved in the physiological regulation of multisite phosphorylation of P1.

Adenosine Triphosphate↗
PubMed1989

Identification of sites on chromosomal protein HMG-I phosphorylated by casein kinase II.

The amino acid sequence of a region on chromosomal protein HMG-I from human cells that is phosphorylated by casein kinase II has been determined. The sequence is: Leu-Glu-Lys-Glu-Glu-Glu-Glu-Gly-Ile-Ser-Gln-Glu-Ser(P)-Ser(P)-Glu-Glu-Gl u-Gln. It corresponds to the C-terminal residues 90-107 of HMG-I [(1989) Mol. Cell. Biol. 9, 2114-2123]. Sequence analysis of the native peptide (90-107) after treatment, which specifically converts phosphoserine residues to S-ethylcysteine, revealed that 70-80% of serine residues 102 and 103 were phosphorylated in vivo. Both residues were fully phosphorylated in vitro by incubation with casein kinase II. These results suggest that casein kinase II is involved in the regulation of HMG-I function in the cells.

Adenosine Triphosphate↗
PubMed1990

Phosphorylation and activation of p40 tyrosine kinase by casein kinase-1.

Because examination of regulatory trans-phosphorylations can help elucidate the cellular functions of tyrosyl protein kinases, we have investigated the effects of phosphorylation by casein kinase-1 on the activity of the p40 tyrosyl protein kinase. We find that casein kinase-1 can phosphorylate the p40 tyrosyl kinase on serine and threonine residues, in part on a unique tryptic peptide. The phosphorylation induces a substantial increase in the tyrosyl protein kinase activity of p40, in contrast to most instances in which serine/threonine phosphorylation inhibits activity of tyrosyl protein kinases. These findings raise the possibility that p40 might be part of a protein phosphorylation network in which casein kinase-1 participates.

Adenosine Triphosphate↗
PubMed1991

The decreased level of casein kinase 2 in brain cortex of schizophrenic and Alzheimer's disease patients.

The content of casein kinase 2 is considerably decreased in ribosome-free extracts of the frontal cortex of schizophrenic and Alzheimer's disease patients in comparison to normal brains as has been demonstrated by means of immunoblotting. The activity of casein kinase 2 towards endogenous substrates and casein is also diminished in the cases of mental pathologies examined. This phenomenon may explain the well-known aberrations in the phosphorylation of structural proteins of human brain which are intrinsic for the mental diseases.

Aged↗
PubMed1993

Identification of casein kinase II as a major endogeneous caldesmon kinase in sheep aorta smooth muscle.

A caldesmon kinase activity was detected in an ATP extract of the myofibril-like pellet from sheep aorta. The enzyme was purified 745-fold and was identified as casein kinase II on the basis of molecular size, substrate specificity, and high sensitivity to heparin inhibition. Casein kinase II phosphorylated isolated caldesmon and caldesmon incorporated into native thin filaments, and transferred about 1 mol of phosphate per mol of caldesmon-h. Ser-73 was the main site phosphorylated by casein kinase II in chicken gizzard caldesmon. Phosphorylation of caldesmon reduced its affinity for smooth muscle myosin but had no effect upon the ability of caldesmon to inhibit the ATPase activity of actomyosin.

Animals↗
PubMed1994

Purification and characterization of casein kinase II from lactating rabbit mammary gland.

1. Highly purified 200 kDa casein kinase II from rabbit lactating mammary gland (MG-CK II) was obtained by means of a new purification procedure consisting of one phosphocellulose and three Monó Q steps. 2. Its Km for ATP was 2.22 microM and 0.57 mg/ml and 0.13 mg/ml for partially dephosphorylated casein and phosvitin respectively. Stathmine was also suitable as substrate. 2-aminopurine and 6-dimethylaminopurine inhibited efficiently MG-CK II (Ki = 5 and 1 mM respectively). 3. MG-CK II autophosphorylated on its alpha-, alpha'- and beta-subunits. The beta-subunit autophosphorylation was enhanced in presence of exogenous substrate. Its modulation was highly dependent on ATP concentration. 4. The effects of basic compounds which affected dramatically the phosphorylation of dephosphorylated casein in presence of various ATP concentrations were reported.

Adenosine Triphosphate↗
PubMed1981

Time course of the development of hypercholesterolemia in rabbits fed semipurified diets containing casein or soybean protein.

The time course of the development of hypercholesterolemia was studied in rabbits fed semipurified diets containing casein or soybean protein. When the rabbits were transferred from a commercial diet to semipurified diets, a rapid increase in the concentration of serum cholesterol and phospholipids occurred. After only one day on the semipurified diets, the cholesterol and phospholipid levels increased by about 50% on the diet containing soybean protein and more than doubled on the diet containing casein. Further elevations were observed after one and two weeks on the diets. However after one month, a decrease in the group on the diet containing soybean protein was found. The increases in serum cholesterol and the differences between the soybean protein and casein group were mainly attributable to differences in the LDL fraction and to a minor extent to differences in the HDL fraction. The feeding of semipurified diets resulted in a steep increase in the ratio of cholesterol to protein in all the lipoprotein fractions after only one day. This suggests that lipoprotein particles relatively rich in cholesterol were formed. Marked variations in the density profile of the serum lipoproteins were observed between individual rabbits fed semipurified diets.

Animals↗
PubMed1988

Effects of soy protein and casein in low cholesterol diets on plasma lipoproteins in normolipidemic subjects.

Dietary plant proteins may lower plasma cholesterol and LDL concentrations in hypercholesterolemic patients when substituted for animal proteins, particularly in diets with low cholesterol and saturated fat content. Plant protein diets appear, however, to be without effect on plasma lipoprotein levels in normal subjects. In the present study, we have examined whether the origin of the dietary protein, i.e. plant (soy) or animal (casein), affects the plasma lipoproteins in normolipidemic subjects when these proteins are presented as components of diets low in cholesterol and saturated fat. The study followed a crossover design. Five men and 5 women consumed liquid formula diets containing 20% of calories as casein or soy protein, 28% as fat (mainly monounsaturated), and 52% as carbohydrate; the intake of cholesterol was less than 100 mg per day. The two dietary periods, each of 1 month duration, were separated by an interim period of 1 month on self-chosen food. Following an initial 30% reduction of cholesterol and LDL plasma levels on both diets, the concentrations of each of the major lipoprotein classes (VLDL, IDL, LDL, HDL2 and HDL3) were similar during the two experimental dietary periods. Body weights were essentially constant. Dietary soy protein and casein could not be distinguished in their effects on the plasma concentrations and chemical composition of the major lipoprotein classes in normolipidemic subjects.

Adult↗
PubMed1989

Effects of cholesterol-free, semipurified diets containing different levels of casein or soy protein on distribution of cholesterol and protein among serum lipoproteins of rabbits.

Rabbits fed cholesterol-free, low-fat, semipurified diets have more cholesterol and protein in serum low density lipoprotein (LDL) relative to high density lipoprotein (HDL) than rabbits fed Chow diet. This difference was accentuated by a casein semipurified diet but was also observed with a soy protein diet even though the latter did not produce an elevation of serum cholesterol. To investigate the reason for these differences, the formulation of the semipurified diets was altered by reducing the level of protein from 27 to 16%, increasing the fat from 1 to 4% and the fiber from 5 to 13%, to correspond more closely to the proportions in Chow. With this formulation, the soy protein diet gave a lipoprotein pattern similar to that of Chow, whereas the casein diet produced a moderately elevated serum cholesterol level with more cholesterol in LDL than in HDL. When the protein in the newly formulated diets was increased back to 27%, the lipoprotein patterns reverted to those obtained with the original formula. In this case, soy protein-fed rabbits had moderately elevated serum cholesterol whereas casein-fed animals showed hypercholesterolemia. These results indicate that the altered lipoprotein pattern observed previously in rabbits fed semipurified diets is related to the high level of protein in those diets.

Animals↗
PubMed1994

Early lesion development in the aortas of rabbits fed low-fat, cholesterol-free, semipurified casein diet.

The initial endothelial morphological alterations and the development of raised, lipid-containing lesions in rabbit aortas were examined after 1 and 3 months on a casein-enriched, semipurified, cholesterol-free diet. The alterations were compared with those in rabbits fed soy-protein in the place of casein and with age-matched, chow-fed, control animals. Using immunohistochemistry macrophages, T-lymphocytes, and smooth muscle cells were identified in the lesions, and an expression of leukocyte adhesion molecules, VCAM-1, ICAM-1 and, occasionally, E-selectin was seen in sections of the aortas of casein-fed rabbits. The initial alterations in the endothelium appear to include evidence of endothelial injury and white blood cell adhesion. No evidence of extracellular liposome formation was observed. This model of atherogenesis is consistent with endothelial injury being an important component of diet-induced atherogenesis and has similarities to human atherosclerosis.

Animals↗
PubMed1993

The analysis of multiple phosphoseryl-containing casein peptides using capillary zone electrophoresis.

Multiple phosphoseryl-containing sequences of peptides and proteins stabilize amorphous calcium phosphate at neutral and alkaline pH and have been implicated in the nucleation/regulation of biomineralization. In an approach to analyze these peptides using capillary zone electrophoresis (CZE) we have attempted to relate the absolute electrophoretic mobility of various casein phosphopeptides to their physicochemical properties. Multiple phosphoseryl-containing peptides were selectively precipitated from enzymic digests of sodium caseinate and further purified using RP-HPLC and anion-exchange fast protein liquid chromatography. Purified fractions were then analyzed by CZE. Absolute electrophoretic mobilities of 13 peptides were determined by measurement of migration times relative to that of a neutral marker, mesityl oxide. A linear relationship (r2 = 0.993) was obtained between absolute electrophoretic mobility and q/M(r)2/3 where q is the net negative charge of the peptide calculated using relevant pKa values and M(r) is the molecular mass. M(r)2/3 is a measure of the surface area of a sphere that has a volume proportional to the M(r) of the peptide and relates to the frictional drag exerted on the peptide during electrophoretic migration. As absolute electrophoretic mobility is influenced by charge and size CZE can be used to monitor peptide phosphorylation, dephosphorylation, deamidation and truncation. This technique therefore would be suitable for quantitative analysis of peptide substrates in kinase and phosphatase studies. In conclusion CZE is a rapid and efficient technique for the resolution of multiple phosphoseryl-containing peptides from enzymic digests of casein.

Amino Acid Sequence↗
PubMed1987

The effects of polyamine antimetabolites on polyamine-responsive casein kinase activity.

The effects of two inhibitors of ornithine decarboxylase activity, alpha-difluoromethylornithine (DMFO) and (2R,5R) 6-heptyne-2,5 diamine (HDA), and an inhibitor of S-adenosylmethionine decarboxylase, methylglyoxal bis-guanylhydrazone (MGBG), were tested on casein kinase activity and endogenous phosphorylation in the cytosol fractions of mouse thyroid and a rat prostate tumor model, Dunning R 3327 MAT LyLu subline. When tested at 5 mM, spermine, DMFO, HDA, and MGBG stimulated mouse thyroid casein kinase activity by 230%, 14%, 65% and 106%, respectively. Similar responses were observed in prostate tumor cytosol. In mouse thyroid cytosol, spermine stimulates 32P incorporation primarily into 3 proteins (MW: 107, 88, and 56 kDa). At 5 mM, MGBG partially reproduces the effects of spermine; HDA is less effective and DMFO is without effect. Similar effects were observed on 3 proteins in prostate tumor cytosol with molecular weights of 91, 41, and 32 kDa. These data provide additional support for the hypothesis that the observed synergistic inhibitory effect of DMFO and MGBG on cell growth may not be due solely to the inhibition of polyamine biosynthesis. Our findings suggest that MGBG-mediated reduction in the phosphorylation of casein kinase substrate should be considered as one locus of action.

Adenocarcinoma↗
PubMed1992

Ingestive/aversive response of rats to sweet stimuli. Influence of glucose, oil, and casein hydrolyzate gastric loads.

Facial consummatory responses reflecting ingestive and aversive perceptions were studied and quantified in rats chronically implanted with gastric and oral catheters. A gustatory stimulus of 50 microliters of 0.6 mol.l-1 sucrose was injected into the mouth every 5 min during 90 min. At time zero, one of seven loads was injected into the stomach. These consisted of, 5 ml of water, or 5 ml solution containing 1 g glucose, 3 g glucose, 1 g casein hydrolyzate, 3 g casein hydrolyzate, or of oil 0.6 ml, or 1.4 ml. The typical ingestive facial consummatory responses in response to sweet stimuli were observed prior to all gastric loads, and also after the water load. On the other hand, the consummatory responses to sweet stimuli turned aversive after all three high-calorie gastric loads. The magnitude of this decrease in palatability (negative alliesthesia) was similar after glucose, casein hydrolyzate, and oil. The reversal of the consummatory responses from ingestive to aversive did not reach the threshold of statistical significance after the three low-calorie gastric loads. These results would tend to show that the intestinal signal for alimentary alliesthesia is nonspecific.

Animals↗
PubMed1996

Effect of kappa-casein split peptides on platelet aggregation and on thrombus formation in the guinea-pig.

An undecapeptide (residues 106-116 of cow kappa-casein) is known to inhibit human platelet aggregation and fibrinogen binding through inhibition of the interaction between the fibrinogen gamma-chain C-terminus and alphaIIbbeta3. This was due to structural homologies with the fibrinogen gamma-chain C-terminal dodecapeptide. We have therefore compared in this work the in vitro anti-aggregating activity of kappa-casein split peptides and their in vivo potential antithrombotic activity in a model of arterial thrombosis triggered by laser-induced intimal injury in the guinea-pig. Caseinoglycopeptide (residues 106-169), the undecapeptide (residues 106-116) and the pentapeptide KNQDK (residues 112-116) from cow kappa-casein, were anti-aggregating peptides and exerted a significant antithrombotic activity in the guinea-pig. Caseinoglycopeptides from three species (cow, ewe and human) were also antithrombotic and the most potent being the human one. The antithrombotic activity was achieved in vivo for doses less than the one suspected from in vitro data and for which, ex vivo platelet aggregation was not decreased. In conclusion, the relative involvement of the fibrinogen gamma-chain C-terminal dodecapeptide could be much more important in in vivo thrombosis process than in in vitro platelet aggregation. Its specificity and activity in vivo unveiled an interesting potential way for inhibition of arterial thrombosis if alternative molecular presentation (i.e. peptidomimetics) and alternative route (i.e. per os) can be developed.

Amino Acid Sequence↗
PubMed1996

Characterization of casein phosphopeptides prepared using alcalase: determination of enzyme specificity.

Tryptic casein phosphopeptides containing the cluster sequence-Ser(P)-Ser(P)-Ser(P)-Glu-Glu- have been shown to stablize amorphous calcium phosphate at neutral and alkaline pH and be anticariogenic in various in vitro, animal and human experiments. Furthermore, metal ion complexes of the casein phosphopeptides (CPPs) have potential as dietetic supplements to increase the bioavailability of calcium, iron, and other essential metal ions. In this study, we have used a Ca2+/ethanol selective precipitation procedure to produce a range of phosphopeptides from an alcalase digest of whole casein. The CPPs released by alcalase were truncated relative to those which are released by trypsin. The peptides could be grouped into those containing the cluster sequence as well as the group of tri-, di-, and monophosphorylated peptides. The two groups contained a number of homologous peptides of varying lengths resulting from the broad specificity of alcalase. Alcalase was observed to cleave peptide bonds on the carboxyl side of Glu, Met, Leu, Tyr, Lys, and Gln; however, of the twenty-six different cleavage sites, seventeen contained a Glu in the P1 position and of these, fifteen contained a hydrophobic residue in either the P2' or P3' positions. Furthermore, of the twenty-six cleavage sites identified, twenty-two contained a hydrophobic residue in either the P2' or P3' positions. Of the four other sites cleaved by alcalase, two contained a hydrophobic residue in the P1' position and one a hydrophobic residue in the P1 position.

Amino Acid Sequence↗
PubMed1986

The proteolytic activity of milk fat, whey and casein for iodinated, extrinsic bovine IgG1, IgG2, SIgA and IgM.

Purified, iodinated bovine immunoglobulins (Igs) were incubated with fresh Guernsey milk or with the casein, fat and whey fraction of such milk for up to 12 hr at 37 degrees C. Igs incubated in whole milk, showed little evidence of proteolysis in either the whey, fat or casein fractions although the amount of radioactivity which became associated with the latter two fractions prevented adequate analysis. When the individual milk fractions were first prepared and then incubated with iodinated Igs, we found no evidence for proteolysis of any Ig in whey or casein but ca. 25% breakdown or dissociation of the IgM and SIgA which had been incubated with milk fat. Breakdown of these Igs in fat was not inhibited with benzamidine-HCl, sodium azide or EDTA. These data show that: only those Igs which associate with milk fat are degraded or dissociated by it and the Ig fragments described from cows milk or recovered during studies on Ig transport cannot be ascribed to the proteolytic activity of fresh milk.

Animals↗
PubMed1996

Casein effects on the myeloperoxidase-mediated oxygen-dependent bactericidal activity of bovine neutrophils.

Effects of casein on the respiratory burst and bactericidal activity of bovine neutrophils were studied in vitro using chemiluminescence measurements of neutrophils and the myeloperoxidase (MPO)/peroxide/chloride bactericidal system in neutrophil-free cultures. At physiological concentrations, casein inhibited the respiratory burst responses of unstimulated bovine neutrophils and those stimulated with opsonized zymosan or phorbol-12-myristate-13-acetate (PMA). The inhibition did not result from impaired activation of neutrophils by the phagocytic stimuli, reduced light transmission or cellular toxicity. Neutrophil respiratory burst activity and the bactericidal activity associated with this phenomenon, i.e. the MPO/peroxide/chloride bactericidal system, were inhibited by casein through the modification of the oxygen radical generating pathway or oxygen radical scavenging. It has long been known that milk inhibits the bactericidal activity of neutrophils. However, the previously undocumented mechanism of action of the major milk protein requires further examination in order to determine whether the neutrophil oxygen-dependent bactericidal pathway plays an important role in defending the lactating bovine udder against bacteria causing mastitis.

Animals↗