CCK receptor dysfunction in muscle membranes from human gallbladders with cholesterol stones.
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Human gallbladders with cholesterol stones exhibit impaired muscle contraction induced by agonists that act on transmembrane receptors, increased membrane cholesterol content, and abnormal cholesterol-to-phospholipid ratio compared with those with pigment stones. The present study was designed to investigate the functions of the CCK receptor of gallbladder muscle membranes by radioreceptor assay and cross-linking. 125I-labeled CCK-8 binding was time-dependent, competitive, and specific. Scatchard analysis showed that the maximum specific binding (Bmax) was significantly decreased in cholesterol compared with pigment stone gallbladders (0.18 +/- 0. 07 vs. 0.38 +/- 0.05 pmol/mg protein, P < 0.05). In contrast, the affinity for CCK was higher in cholesterol than pigment stone gallbladders (0.18 +/- 0.06 vs. 1.2 +/- 0.23 nM). Similar results were observed in binding studies with the CCK-A receptor antagonist [3H]L-364,718. Cross-linking and saturation binding studies also showed significantly less CCK binding in gallbladders with cholesterol stones. These abnormalities were reversible after incubation with cholesterol-free liposomes. The Bmax increased (P < 0.01) and the dissociation constant decreased (P < 0.001) after incubation with cholesterol-free liposomes. In conclusion, human gallbladders with cholesterol stones have impaired CCK receptor binding compared with those with pigment stones. These changes are reversed by removal of the excess membrane cholesterol. These receptor alterations may contribute to the defective contractility of the gallbladder muscle in patients with cholesterol stones. (+info)
Fluorescence polarization studies on four biliproteins and a bilin model for phycoerythrin 545.
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Fluorescence (excitation) polarization spectroscopy in the wavelength region of the bilin chromophores was applied to phycoerythrocyanin (CV-phycocyanin), phycocyanins 645 and 612, and phycoerythrin 545. The cryptomonad biliproteins - phycoerythrin 545 and phycocyanins 612 and 645 - were studied as both protein dimers having an alpha(2)beta(2) polypeptide structure and as alphabeta monomers. The cyanobacterial phycoerythrocyanin (CV-phycocyanin) was a trimeric oligomer. The changes in polarization across the spectrum were attributed to transfers of energy between bilins. Cryptomonad biliproteins are isolated as dimers. The similarities between their steady-state fluorescence polarization spectra and those of the corresponding monomers suggested that the monomers' conformations were analogous to the dimers. This supports the use of monomers in the study of dimer bilin organization. The unusual polarization spectrum of phycoerythrin 545 was explained using a model for the topography of its bilins. Obtaining the emission spectra of phycoerythrin 545 at several temperatures and a deconvolution of the dimer circular dichroism spectrum also successfully tested the bilin model. Circular dichroism spectroscopy was used to determine which polarization changes are formed by Forster resonance energy transfers and which may be produced by internal conversions between high- and low-energy states of pairs of exciton-coupled bilins. Attempts were made to assign energy transfer events to the corresponding changes in fluorescence polarization for each of the four biliproteins. (+info)
In vitro assembly of phytochrome B apoprotein with synthetic analogs of the phytochrome chromophore.
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Phytochrome B (PhyB), one of the major photosensory chromoproteins in plants, mediates a variety of light-responsive developmental processes in a photoreversible manner. To analyze the structural requirements of the chromophore for the spectral properties of PhyB, we have designed and chemically synthesized 20 analogs of the linear tetrapyrrole (bilin) chromophore and reconstituted them with PhyB apoprotein (PHYB). The A-ring acts mainly as the anchor for ligation to PHYB, because the modification of the side chains at the C2 and C3 positions did not significantly influence the formation or difference spectra of adducts. In contrast, the side chains of the B- and C-rings are crucial to position the chromophore properly in the chromophore pocket of PHYB and for photoreversible spectral changes. The side-chain structure of the D-ring is required for the photoreversible spectral change of the adducts. When methyl and ethyl groups at the C17 and C18 positions are replaced with an n-propyl, n-pentyl, or n-octyl group, respectively, the photoreversible spectral change of the adducts depends on the length of the side chains. From these studies, we conclude that each pyrrole ring of the linear tetrapyrrole chromophore plays a different role in chromophore assembly and the photochromic properties of PhyB. (+info)
Sequence of heme decomposition by the coupled oxidation of myoglobin with ascorbic acid.
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Occurrence of a biliverdin-iron complex or verdoheme as the final oxidation product of heme moiety in the coupled oxidation of myoglobin and ascorbic acid in air was evidenced and the sequence of heme decomposition in this reaction system was concluded to proceed in the order of protoheme, hydroxyheme and biliverdin-iron complex or verdoheme. The final oxidation product usually remains attaached to globin and appears to give a diffuse absorption possibly with a peak at 760 nm at neutral pH. In alkaline solution the compound exhibits an absorption peak at 840 nm, and when reduced with Na(2)S(2)O(4), it is readily converted to biliverdin which exhibits a large absorption with a peak originally at 800 nm, being followed by a gradual shift to 760 nm. (+info)
Effect of metiamide on the response to secretin and cholecystokinin in man.
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The effects of intravenous metiamide on the pancreatic exocrine response to intravenous infusion of secretin plus cholecystokinin has been studied in eight patients with duodenal ulceration. The secretion of bicarbonate and water was not altered by metiamide. The secretion of enzymes was significantly less than control during infusion of metiamide. The differences between the pancreatic and gastric responses to metiamide are discussed. (+info)
Bile bilirubin pigment analysis in disorders of bilirubin metabolism in early infancy.
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BACKGROUND: Early and accurate diagnosis of Crigler-Najjar syndrome, which causes prolonged unconjugated hyperbilirubinaemia in infancy, is important, as orthotopic liver transplantation is the definitive treatment. AIM: To determine whether bilirubin pigment analysis of bile in infants with prolonged unconjugated hyperbilirubinaemia provides useful diagnostic information in the first 3 months of life. METHODS: Retrospective review of patients with prolonged unconjugated hyperbilirubinaemia referred to the liver unit, Birmingham Children's Hospital, for the diagnosis of Crigler-Najjar syndrome. Bile bilirubin pigment composition was determined by high performance liquid chromatography. Initial diagnoses were made based on the result of bile bilirubin pigment composition. Final diagnoses were made after reviewing the clinical course, response to phenobarbitone, repeat bile bilirubin pigment composition analysis, and genetic studies. RESULTS: Between 1992 and 1999, nine infants aged less than 3 months of age with prolonged hyperbilirubinaemia underwent bile bilirubin pigment analyses. Based on these, two children were diagnosed with Crigler-Najjar syndrome (CNS) type 1, six with CNS type 2, and one with Gilbert's syndrome. Five children whose initial diagnosis was CNS type 2 had resolution of jaundice and normalisation of serum bilirubin after discontinuing phenobarbitone, and these cases were thought to be normal or to have Gilbert's syndrome. One of the initial cases of CNS type 1 responded to phenobarbitone with an 80% reduction in serum bilirubin consistent with CNS type 2. In all, the diagnoses of six cases needed to be reviewed. CONCLUSIONS: Early bile pigment analysis, performed during the first 3 months of life, often shows high levels of unconjugated bilirubin or bilirubin monoconjugates, leading to the incorrect diagnosis of both type 1 and type 2 Crigler-Najjar syndrome. (+info)
Separation by thin-layer chromatography and structure elucidation of bilirubin conjugates isolated from dog bile.
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1. A system for separation of bile pigments by t.l.c. and for their structure elucidation is presented. Separated bile pigments are characterized by t.l.c. of derived dipyrrolic azopigments. 2. At the tetrapyrrolic stage hydrolysis in strongly alkaline medium followed by t.l.c. demonstrates the presence of bilirubin-IIIalpha, -IXalpha and -XIIIalpha and allows assessment of their relative amounts. 3. Most structural information is derived from analysis of dipyrrolic azopigments. Such derivatives, obtained by treatment of separated bile pigments with diazotized ethyl anthranilate, were separated and purified by t.l.c. Micro methods showed (a) the nature of the dipyrrolic aglycone, (b) the nature of the bonds connecting aglycone to a conjugating group, (c) the ratio of vinyl/isovinyl isomers present in the aglycone and, (d) the nature of the conjugating groups (by suitable derivative formation and t.l.c. with reference to known compounds). 4. In bile of normal dogs at least 20 tetrapyrrolic, diazo-positive bile pigments could be recognized. Except for two pigments the tetrapyrrolic nucleus corresponded predominantly to bilirubin-IXalpha. All conjugated pigments had their conjugating groups connected in ester linkage to the tetrapyrrolic aglycone, Apart from bilirubin-IXalpha, monoconjugates and homogeneous and mixed diconjugates of bilirubin were demonstrated; conjugating groups of major importance were xylose, glucose and glucuronic acid. 5. Bilirubin isomer determination on native bile and isolated bile pigments, and dipyrrole-exchange assays with [14C8]bilirubin indicated (a) that the conjugates pre-exist in bile, and (b) that no significant dipyrrole exchange occurs during isolation of the pigments. (+info)
Recombinant holophytochrome in Escherichia coli.
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We have successfully co-expressed two genes from the bilin biosynthetic pathway of Synechocystis together with cyanobacterial phytochrome 1 (Cph1) from the same organism to produce holophytochrome in Escherichia coli. Heme oxygenase was used to convert host heme to biliverdin IXalpha which was then reduced to phycocyanobilin via phycocyanobilin:ferredoxin oxidoreductase, presumably with the aid of host ferredoxin. In this host environment Cph1 apophytochrome was able to autoassemble with the phycocyanobilin in vivo to form fully photoreversible holophytochrome. The system can be used as a tool for further genetic studies of phytochrome function and signal transduction as well as providing an excellent source of holophytochrome for physicochemical studies. (+info)