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At least 199 records · Page 11Linked to original sources
PubMed1983

Intestinal absorption of calcium in rats given diets containing casein or amino acid mixture: the role of casein phosphopeptides.

1. In an attempt to investigate calcium absorption in the rat during the postprandial period, with the least alteration of the physical environment, the undisturbed small intestine was ligated in situ 2.5 or 3.0 h after ingestion of a diet containing 200 g casein/kg or an equivalent amino acid mixture, or 925 g casein/kg. Estimation of Ca absorption was made by comparing the amount of soluble 40Ca or 45Ca in the contents of segments from the rats receiving 45Ca by intubation 30 min after withdrawal of food, ligated after a further 30 min, then killed after 0 or 30 min. 2. Under conditions such that the estimated amount of a marker, polyethylene glycol, in segments ligated in a defined position was little changed in rats killed 30 min apart, the difference in the amount of soluble 40Ca was much higher in the rats fed on the basal diet containing 200 g casein/kg than in other groups. 3. This specific effect on Ca absorption, particularly in the distal portion of the small intestine, could be seen also after 45Ca was directly injected into ligated segments in situ. The amount of 45Ca in the portal blood 15 min after injection of the label was also highest in the rats given the basal diet. 4. The results were in agreement with our previous findings that the formation and accumulation of casein phosphopeptides causes an increase in the amount of soluble Ca in the distal small intestine.

Amino Acids↗
PubMed1993

Ser2 is the autophosphorylation site in the beta subunit from bicistronically expressed human casein kinase-2 and from native rat liver casein kinase-2 beta.

Human casein kinase-2 (CK-2) subunits alpha and beta were bicistronically expressed in bacteria. The recombinant holoenzyme shared all investigated properties with the native CK-2 from mammalian sources (rat liver, Krebs II mouse ascites tumour cells). Contrary to recombinant human CK-2 produced by self-assembly in vitro, the bicistronically expressed beta subunit was autophosphorylated during formation of the holoenzyme in bacteria. Electrospray ionisation mass spectrometry (ESI) revealed Ser2 (second amino acid, first serine) as the only phosphate acceptor site. Kinetic data obtained with either the phosphorylated or the unphosphorylated form of CK-2 did not differ significantly, suggesting that the autophosphorylation had no influence on the kinetic parameters Km and Vmax. In parallel, native rat liver CK-2 beta subunit was shown to incorporate 0.1 mol phosphate/mol holoenzyme, which suggests that the enzyme is already heavily phosphorylated. ESI analysis also revealed Ser2 as the only phosphorylated residue at the amino terminus. In the case of both recombinant human CK-2 and native rat liver CK-2, treatment with alkaline phosphatase readily reversed the phosphorylated form of the beta subunit to the faster migrating dephosphorylated polypeptide.

Amino Acid Sequence↗
PubMed1979

Novel opioid peptides derived from casein (beta-casomorphins). I. Isolation from bovine casein peptone.

A material which displayed opioid activity in the guinea pig ileum longitudinal muscle-myenteric plexus preparation was extracted from an enzymatic casein digest into chloroform/methanol. The extract was roughly purified by adsorption/desorption procedures using charcoal and Amberlite XAD-2 resin as adsorbents. A high degree of purity was achieved by high-pressure liquid chromatography of the material on muBondapak C18 and mu-Porasil columns and finally by gel filtration chromatography on a Bio-Gel P-2 column. Several pronase-resistant compounds with opioid activity were obtained.

Animals↗
PubMed1995

A 1H-NMR study of the casein phosphopeptide alpha s1-casein(59-79).

Complete sequence-specific resonance assignments have been determined for a calcium phosphate sequestering, phosphoseryl-containing, tryptic peptide alpha s1-casein(59-79) containing the phosphorylated motif -SSSEE-. Spectra have been recorded in the presence of excess Ca2+ and at three different values of sample pH to characterize the changes in peptide conformation as calcium binds to the phosphorylated residues. The secondary structure of the peptide was characterized by sequential (i,i + 1), medium-range (i,i + 2/3/4), and long-range (i,i + 5) NOE connectivities, C alpha H chemical shifts, NH to C alpha H coupling constants and the observation of slowly exchanging amide protons. Two structured regions have been identified: residues P73 to V76 implicated in beta-turn conformations, and residues E61 to sigma 67 involved in a loop-type structure.

Amino Acid Sequence↗
PubMed1995

High-level, stage- and mammary-tissue-specific expression of a caprine kappa-casein-encoding minigene driven by a beta-casein promoter in transgenic mice.

A 5' truncated caprine (ca) kappa-casein-encoding gene (kappa Cas) was fused to the 3' end of a 3' truncated ca beta Cas. The kappa Cas form comprised the 0.8-kb 3' end of intron 2, the remaining part of the transcription unit containing codons -2 to stop 172, and 0.43 kb of the 3' flanking region. The beta Cas form comprised a 3-kb 5' flanking region and the 5' end of the transcription unit terminating 69 bp downstream from exon 2 which encodes the 15-amino-acid (aa) signal peptide and the first 2 aa of mature beta Cas. The resulting hybrid gene driven by the beta Cas promoter was expressed in all eight lines of transgenic mice investigated, although at different levels. In two lines, the yield of recombinant (re-) kappa Cas was > or = 3 mg/ml of milk. The stage- and mammary tissue-specific expression was similar to that of endogenous beta Cas. The re-kappa Cas differed from its goat milk counterpart by the occurrence of four extra aa at the N-terminal end, indicating that the signal peptidase released the beta Cas signal peptide. According to sedimentation analyses of murine milk containing > or = 3 mg re-kappa Cas/ml, the latter essentially occurred in micelles. Preliminary comparative assays of the behavior of ca alpha s1Cas-kappa Cas and alpha s1Cas-re-kappa Cas mixtures upon incremental addition of Ca2+ showed that re-kappa Cas had the capacity to protect alpha s1Cas against Ca(2+)-induced precipitation in forming stable micelles.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed2002

Casein kinase I and casein kinase II differentially regulate axin function in Wnt and JNK pathways.

Axin uses different combinations of functional domains in down-regulation of the Wnt pathway and activation of the MEKK1/JNK pathway. We are interested in the elucidation of the functional switch of Axin. In the present study, we show that the Wnt activator CKIepsilon, but not CKIIalpha, Frat1, LRP5, or LRP6, inhibited Axin-mediated JNK activation. We also found that both CKIalpha and CKIepsilon interacted with Axin, whereas CKIIalpha did not bind to Axin and had no effect on Axin-mediated JNK activity even though CKIIalpha has also been suggested to be an activator for the Wnt pathway. The COOH-terminal region and the MEKK1-interacting domain of Axin are important for CKIalpha-Axin and CKIepsilon-Axin interaction. We further demonstrated that CKIepsilon and CKIalpha binding to Axin excluded MEKK1 binding, indicating that a competitive physical occupancy may underlie the inhibitory effect. Moreover, our data indicated that CKIepsilon kinase activity plays an additive role in this effect. Taken together, we have demonstrated that CKI and CKII exhibit differential effects on Axin-MEKK1 interaction and Axin-mediated JNK activation. Furthermore, our data suggest that CKI may provide a possible switch mechanism for Axin function in the regulation of Wnt and JNK pathways.

Animals↗