Photoreversible Aggregation of the Biliprotein Containing the First and Second GAF Domains of a Cyanobacteriochrome All2699 in Nostoc sp. PCC7120

As plant photoreceptors, phytochromes are capable of detecting red light and far-red light, thereby governing plant growth. All2699 is a photoreceptor found in Nostoc sp. PCC7120 that specifically responds to red light and far-red light. All2699g1g2 is a truncated protein carrying the first and second GAF (cGMP phosphodiesterase/adenylyl cyclase/FhlA) domains of All2699. In this study, we found that, upon exposure to red light, the protein underwent aggregation, resulting in the formation of protein aggregates. Conversely, under far-red light irradiation, these protein aggregates dissociated. We delved into the factors that impact the aggregation of All2699g1g2, focusing on the protein structure. Our findings showed that the GAF2 domain contains a low-complexity (LC) loop region, which plays a crucial role in mediating protein aggregation. Specifically, phenylalanine at position 239 within the LC loop region was identified as a key site for the aggregation process. Furthermore, our research revealed that various factors, including irradiation time, temperature, concentration, NaCl concentration, and pH value, can impact the aggregation of All2699g1g2. The aggregation led to variations in Pfr concentration depending on temperature, NaCl concentration, and pH value. In contrast, ΔLC did not aggregate and therefore lacked responses to these factors. Consequently, the LC loop region of All2699g1g2 extended and enhanced sensory properties.

Zinc-Induced Fluorescence Turn-On in Native and Mutant Phycoerythrobilin-Binding Orange Fluorescent Proteins

Cyanobacteriochrome (CBCR)-derived fluorescent proteins are a class of reporters that can bind bilin cofactors and fluoresce across the ultraviolet to the near-infrared spectrum. Derived from phytochrome-related photoreceptor proteins in cyanobacteria, many of these proteins use a single small GAF domain to autocatalytically bind a bilin and fluoresce. The second GAF domain of All1280 (All1280g2) from Nostoc sp. PCC7120 is a DXCF motif-containing protein that exhibits blue-light-responsive photochemistry when bound to its native cofactor, phycocyanobilin. All1280g2 can also bind non-photoswitching phycoerythrobilin (PEB), resulting in a highly fluorescent protein. Given the small size, high quantum yield, and that unlike green fluorescent proteins, bilin-binding proteins can be used in anaerobic organisms, the orange fluorescent All1280g2-PEB protein is a promising platform for designing new genetically encoded metal ion sensors. Here, we show that All1280g2-PEB undergoes a ∼5-fold reversible zinc-induced fluorescence enhancement with a blue-shifted emission maximum (572 to 517 nm), which is not observed for a related PEB-bound GAF from Synechocystis sp. PCC6803 (Slr1393g3). Zn2+ significantly enhances All1280g2-PEB fluorescence across a biologically relevant pH range from 6.0 to 9.0, with pH-dependent dissociation constants from 1 μM to ∼20-80 nM. Site-directed mutants aiming to sterically decrease and increase access to PEB show a decreased and similar amount of zinc-induced fluorescence enhancement. Mutation of the cysteine residue within the DXCF motif to alanine abolishes the zinc-induced fluorescence enhancement. Collectively, these results support the presence of a unique fluorescence-enhancing Zn2+ binding site in All1280g2-PEB likely involving coordination to the bilin cofactor and requiring a nearby cysteine residue.

On the evolution of the plant phytochrome chromophore biosynthesis

Phytochromes are biliprotein photoreceptors present in plants, algae, certain bacteria, and fungi. Land plant phytochromes use phytochromobilin (PΦB) as the bilin chromophore. Phytochromes of streptophyte algae, the clade within which land plants evolved, employ phycocyanobilin (PCB), leading to a more blue-shifted absorption spectrum. Both chromophores are synthesized by ferredoxin-dependent bilin reductases (FDBRs) starting from biliverdin IXα (BV). In cyanobacteria and chlorophyta, BV is reduced to PCB by the FDBR phycocyanobilin:ferredoxin oxidoreductase (PcyA), whereas, in land plants, BV is reduced to PФB by phytochromobilin synthase (HY2). However, phylogenetic studies suggested the absence of any ortholog of PcyA in streptophyte algae and the presence of only PФB biosynthesis-related genes (HY2). The HY2 of the streptophyte alga Klebsormidium nitens (formerly Klebsormidium flaccidum) has already indirectly been indicated to participate in PCB biosynthesis. Here, we overexpressed and purified a His6-tagged variant of K. nitens HY2 (KflaHY2) in Escherichia coli. Employing anaerobic bilin reductase activity assays and coupled phytochrome assembly assays, we confirmed the product and identified intermediates of the reaction. Site-directed mutagenesis revealed 2 aspartate residues critical for catalysis. While it was not possible to convert KflaHY2 into a PΦB-producing enzyme by simply exchanging the catalytic pair, the biochemical investigation of 2 additional members of the HY2 lineage enabled us to define 2 distinct clades, the PCB-HY2 and the PΦB-HY2 clade. Overall, our study gives insight into the evolution of the HY2 lineage of FDBRs.

The specificity of the bilin lyase CpcS for chromophore attachment to allophycocyanin in the chlorophyll f-containing cyanobacterium Halomicronima hongdechloris

Phycobilisomes are light-harvesting antenna complexes of cyanobacteria and red algae that are comprised of chromoproteins called phycobiliproteins. PBS core structures are made up of allophycocyanin subunits. Halomicronema hongdechloris (H. hongdechloris) is one of the cyanobacteria that produce chlorophyll f (Chl f) under far-red light and is regulated by the Far-Red Light Photoacclimation gene cluster. There are five genes encoding APC in this specific gene cluster, and they are responsible for assembling the red-shifted PBS in H. hongdechloris grown under far-red light. In this study, the five apc genes located in the FaRLiP gene cluster were heterologously expressed in an Escherichia coli reconstitution system. The canonical APC-encoding genes were also constructed in the same system for comparison. Additionally, five annotated phycobiliprotein lyase-encoding genes (cpcS) from the H. hongdechloris genome were phylogenetically classified and experimentally tested for their catalytic properties including their contribution to the shifted absorption of PBS. Through analysis of recombinant proteins, we determined that the heterodimer of CpcS-I and CpcU are able to ligate a chromophore to the APC-α/APC-β subunits. We discuss some hypotheses towards understanding the roles of the specialised APC and contributions of PBP lyases.

Crystal structure of a far-red-sensing cyanobacteriochrome reveals an atypical bilin conformation and spectral tuning mechanism

Cyanobacteriochromes (CBCRs) are small, linear tetrapyrrole (bilin)-binding photoreceptors in the phytochrome superfamily that regulate diverse light-mediated adaptive processes in cyanobacteria. More spectrally diverse than canonical red/far-red-sensing phytochromes, CBCRs were thought to be restricted to sensing visible and near UV light until recently when several subfamilies with far-red-sensing representatives (frCBCRs) were discovered. Two of these frCBCRs subfamilies have been shown to incorporate bilin precursors with larger pi-conjugated chromophores, while the third frCBCR subfamily uses the same phycocyanobilin precursor found in the bulk of the known CBCRs. To elucidate the molecular basis of far-red light perception by this third frCBCR subfamily, we determined the crystal structure of the far-red-absorbing dark state of one such frCBCR Anacy_2551g3 from Anabaena cylindrica PCC 7122 which exhibits a reversible far-red/orange photocycle. Determined by room temperature serial crystallography and cryocrystallography, the refined 2.7-Å structure reveals an unusual all-Z,syn configuration of the phycocyanobilin (PCB) chromophore that is considerably less extended than those of previously characterized red-light sensors in the phytochrome superfamily. Based on structural and spectroscopic comparisons with other bilin-binding proteins together with site-directed mutagenesis data, our studies reveal protein-chromophore interactions that are critical for the atypical bathochromic shift. Based on these analyses, we propose that far-red absorption in Anacy_2551g3 is the result of the additive effect of two distinct red-shift mechanisms involving cationic bilin lactim tautomers stabilized by a constrained all-Z,syn conformation and specific interactions with a highly conserved anionic residue.

The Arabidopsis CRUMPLED LEAF protein, a homolog of the cyanobacterial bilin lyase, retains the bilin-binding pocket for a yet unknown function

The photosynthetic bacterial phycobiliprotein lyases, also called CpcT lyases, catalyze the biogenesis of phycobilisome, a light-harvesting antenna complex, through the covalent attachment of chromophores to the antenna proteins. The Arabidopsis CRUMPLED LEAF (CRL) protein is a homolog of the cyanobacterial CpcT lyase. Loss of CRL leads to multiple lesions, including localized foliar cell death, constitutive expression of stress-related nuclear genes, abnormal cell cycle, and impaired plastid division. Notwithstanding the apparent phenotypes, the function of CRL still remains elusive. To gain insight into the function of CRL, we examined whether CRL still retains the capacity to bind with the bacterial chromophore phycocyanobilin (PCB) and its plant analog phytochromobilin (PΦB). The revealed structure of the CpcT domain of CRL is comparable to that of the CpcT lyase, despite the low sequence identity. The subsequent in vitro biochemical assays found, as shown for the CpcT lyase, that PCB/PΦB binds to the CRL dimer. However, some mutant forms of CRL, substantially compromised in their bilin-binding ability, still restore the crl-induced multiple lesions. These results suggest that although CRL retains the bilin-binding pocket, it seems not functionally associated with the crl-induced multiple lesions.

Characterization of the pheophorbide a oxygenase/phyllobilin pathway of chlorophyll breakdown in grasses

Although the PAO/phyllobilin pathway of chlorophyll breakdown is active in grass leaf senescence, the abundance of phyllobilins is far below the amount of degraded chlorophyll. The yellowing of fully developed leaves is the most prominent visual symptom of plant senescence. Thereby, chlorophyll is degraded via the so-called pheophorbide a oxygenase (PAO)/phyllobilin pathway to a species-specific set of phyllobilins, linear tetrapyrrolic products of chlorophyll breakdown. Here, we investigated the diversity and abundance of phyllobilins in cereal and forage crops, i.e. barley, rice, ryegrass, sorghum and wheat, using liquid chromatography-mass spectrometry. A total of thirteen phyllobilins were identified, among them four novel, not yet described ones, pointing to a rather high diversity of phyllobilin-modifying activities present in the Gramineae. Along with these phyllobilins, barley orthologs of known Arabidopsis thaliana chlorophyll catabolic enzymes were demonstrated to localize in the chloroplast, and two of them, i.e. PAO and pheophytin pheophorbide hydrolase, complemented respective Arabidopsis mutants. These data confirm functionality of the PAO/phyllobilin pathway in grasses. Interestingly, when comparing phyllobilin abundance with amounts of degraded chlorophyll in senescent leaves, in most analyzed grass species only minor fractions of chlorophyll were recovered as phyllobilins, opposite to A. thaliana where phyllobilin quantities match degraded chlorophyll rather well. These data show that, despite the presence and activity of the PAO/phyllobilin pathway in barley (and other cereals), phyllobilins do not accumulate stoichiometrically, implying possible degradation of chlorophyll beyond the phyllobilin level.

Decomposition of cyanobacterial light harvesting complexes: NblA-dependent role of the bilin lyase homolog NblB

Phycobilisomes, the macromolecular light harvesting complexes of cyanobacteria are degraded under nutrient-limiting conditions. This crucial response is required to adjust light excitation to the metabolic status and avoid damage by excess excitation. Phycobilisomes are comprised of phycobiliproteins, apo-proteins that covalently bind bilin chromophores. In the cyanobacterium Synechococcus elongatus, the phycobiliproteins allophycocyanin and phycocyanin comprise the core and the rods of the phycobilisome, respectively. Previously, NblB was identified as an essential component required for phycocyanin degradation under nutrient starvation. This protein is homologous to bilin-lyases, enzymes that catalyze the covalent attachment of bilins to apo-proteins. However, the nblB-inactivated strain is not impaired in phycobiliprotein synthesis, but rather is characterized by aberrant phycocyanin degradation. Here, using a phycocyanin-deficient strain, we demonstrate that NblB is required for degradation of the core pigment, allophycocyanin. Furthermore, we show that the protein NblB is expressed under nutrient sufficient conditions, but during nitrogen starvation its level decreases about two-fold. This finding is in contrast to an additional component essential for degradation, NblA, the expression of which is highly induced under starvation. We further identified NblB residues required for phycocyanin degradation in vivo. Finally, we demonstrate phycocyanin degradation in a cell-free system, thereby providing support for the suggestion that NblB directly mediates pigment degradation by chromophore detachment. The dependence of NblB function on NblA revealed using this system, together with the results indicating presence of NblB under nutrient sufficient conditions, suggests a rapid mechanism for induction of pigment degradation, which requires only the expression of NblA.

Ferredoxin-dependent bilin reductases in eukaryotic algae: Ubiquity and diversity

Linear tetrapyrroles (bilins) are produced from heme by heme oxygenase, usually forming biliverdin IXα (BV). Fungi and bacteria use BV as chromophore for phytochrome photoreceptors. Oxygenic photosynthetic organisms use BV as a substrate for ferredoxin-dependent bilin reductases (FDBRs), enzymes that produce diverse reduced bilins used as light-harvesting pigments in phycobiliproteins and as photoactive photoreceptor chromophores. Bilin biosynthesis is essential for phototrophic growth in Chlamydomonas reinhardtii despite the absence of phytochromes or phycobiliproteins in this organism, raising the possibility that bilins are more generally required for phototrophic growth by algae. We here leverage the recent expansion in available algal transcriptomes, cyanobacterial genomes, and environmental metagenomes to analyze the distribution and diversification of FDBRs. With the possible exception of euglenids, FDBRs are present in all photosynthetic eukaryotic lineages. Phylogenetic analysis demonstrates that algal FDBRs belong to the three previously recognized FDBR lineages. Our studies provide new insights into FDBR evolution and diversification.

Breakdown of Chlorophyll in Higher Plants--Phyllobilins as Abundant, Yet Hardly Visible Signs of Ripening, Senescence, and Cell Death

Fall colors have always been fascinating and are still a remarkably puzzling phenomenon associated with the breakdown of chlorophyll (Chl) in leaves. As discovered in recent years, nongreen bilin-type Chl catabolites are generated, which are known as the phyllobilins. Collaborative chemical-biological efforts have led to the elucidation of the key Chl-breakdown processes in senescent leaves and in ripening fruit. Colorless and largely photoinactive phyllobilins are rapidly produced from Chl, apparently primarily as part of a detoxification program. However, fluorescent Chl catabolites accumulate in some senescent leaves and in peels of ripe bananas and induce a striking blue glow. The structural features, chemical properties, and abundance of the phyllobilins in the biosphere suggest biological roles, which still remain to be elucidated.

Molecular Cloning of cpcU and Heterodimeric Bilin Lyase Activity Analysis of CpcU and CpcS for Attachment of Phycocyanobilin to Cys-82 on the β-Subunit of Phycocyanin in Arthrospira platensis FACHB314

A new bilin lyase gene cpcU was cloned from Arthrospira platensis FACHB314 to study the assembly of the phycocyanin β-Subunit. Two recombinant plasmids, one contained the phycocyanobilin (PCB) producing genes (hoxI and pcyA), while the other contained the gene of the β-Subunit of phycobiliprotein (cpcB) and the lyase gene (cpcU, cpcS, or cpcU/S) were constructed and separately transferred into Escherichia coli in order to test the activities of relevant lyases for catalyzing PCB addition to CpcB during synthesizing fluorescent β-PC of A. platensis FACHB314. The fluorescence intensity examination showed that Cys-82 maybe the active site for the β-Subunit binding to PCBs and the attachment could be carried out by CpcU, CpcS, or co-expressed cpcU/S in A. platensis FACHB314.

Adjusting to a sudden “aging” of the lens

Color perception is known to remain largely stable across the lifespan despite the pronounced changes in sensitivity from factors such as the progressive brunescence of the lens. However, the mechanisms and timescales controlling these compensatory adjustments are still poorly understood. In a series of experiments, we tracked adaptation in observers after introducing a sudden change in lens density by having observers wear glasses with yellow filters that approximated the average spectral transmittance of a 70-year-old lens. Individuals were young adults and wore the glasses for 5 days for 8 h per day while engaged in their normal activities. Achromatic settings were measured on a CRT before and after each daily exposure with the lenses on and off, and were preceded by 5 min of dark adaptation to control for short-term chromatic adaptation. During each day, there was a large shift in the white settings consistent with a partial compensation for the added lens density. However, there was little to no evidence of an afterimage at the end of each daily session, and participants’ perceptual nulls were roughly aligned with the nulls for short-term chromatic adaptation, suggesting a rapid renormalization when the lenses were removed. The long-term drift was also extinguished by brief exposure to a white adapting field. The results point to distinct timescales and potentially distinct mechanisms compensating for changes in the chromatic sensitivity of the observer.

Effect of bile pigments on the compromised gut barrier function in a rat model of bile duct ligation

Background

Studies have shown that the absence of bile in the gut lumen, either by bile duct ligation or bile diversion, induces mucosal injury. However, the mechanism remains elusive. In this study, the role of bile pigments in gut barrier function was investigated in a rat model of bile duct ligation.

Methods

Male Sprague Dawley (SD) rats were used in this study. After ligation of bile duct, the animals were administrated with free bilirubin, bilirubin ditaurate, or biliverdin by intragastric gavage. 1, 2, or 3 days later, the animals were sacrificed and the damage of mucosa was assessed by histological staining as well as biochemical parameters such as changes of diamine oxidase (DAO) and D-lactate (D-Lac) in the blood. Trypsin and chymotrypsin of the gut were also measured to determine how these digestive proteases may relate to the observed effects of bile pigments.

Results

Bile duct ligation (BDL) caused significant increases in gut trypsin and chymotrypsin along with damage of the mucosa as demonstrated by the histological findings under microscope, the reduced expression of tight junction molecules like occludin, and significant changes in DAO and D-lac in the blood. Free bilirubin but not bilirubin ditaurate or biliverdin showed significant inhibitions on trypsin and chymotrypsin as well as alleviated changes of histological and biochemical parameters related to gut barrier disruption.

Conclusion

Bile may protect the gut from damage through inhibiting digestive proteases like trypsin and chymotrypsin by free bilirubin.

[Indicators of exchange of bile pigments under the action of ecopathogenic factors on the organism and correction with liposomes]

High levels of anthropogenic impact on the environment requires a detailed study of the features of the influence of heavy metals and ionizing radiation on living organisms, and provides for the development and use of effective means of protecting the body from its negative influence. The purpose of the work was to study the characteristics of the exchange of bile pigments of rats under the action of ecopathogenic factors (ionizing radiation and cadmium) on the organism and the corrective properties of liposomes on the basis of milk phospholipids. An analysis of the chromatographic studies of bilirubin and derivatives (nonconjugated bilirubin, bilirubin sulfate, billirubin glucuronide, urobilin and stercobilin) in the whole blood, liver, jejunum contents and feces under the action on the animal organism of ecopathogenic factors (ionizing radiation and cadmium) indicate material violation of the exchange bile pigments that may be due to the destabilization of the structural and functional hot hepatocytes. Correction of the liposomal form of biologically active additive (BAA) FLP-MD is recommended; the latter is a mixture of phospholipids isolated from milk, with a mixture of unsaturated fatty acids (oleic, linoleic, linolenic) and antioxidants (alpha-tocopherol and retinol acetate). The additive components exhibit the reparative effect of the action in respect of the damaged membrane structures with simultaneous improving of cholepoietic and billiation liver function, and therefore contribute to the normalization of exchange og bile pigments in terms of action on the body ecopathogenic factors.

Molecular cloning and expression analysis of a new bilin lyase: the cpcT gene encoding a bilin lyase responsible for attachment of phycocyanobilin to Cys-153 on the β-subunit of phycocyanin in Arthrospira platensis FACHB314

To study the assembly of phycocyanin β subunit, the gene cpcT was first cloned from Arthrospira platensis FACHB314. To explore the function of cpcT, the DNA of phycocyanin β subunit and cpcT were transformed into Escherichia coli BL21 with the plasmid pET-hox1-pcyA, which contained the genes hemeoxygenase 1 (Hox1) and ferredoxin oxidoreductase (PcyA) needed to produce phycocyanobilin. The transformed strains showed specific phycocyanin fluorescence, and the fluorescence intensity was stronger than the strains with only phycocyanin β subunit, indicating that CpcT can promote the assembly of phycocyanin to generate fluorescence. To study the possible binding sites of apo-phycocyanin and phycocyanobilin, the Cys-82 and Cys-153 of the β subunit were individually mutated, giving two kinds of mutants. The results show that Cys-153 maybe the active site for β subunit binding to phycocyanobilins, which is catalyzed by CpcT in A. platensis FACHB314.

PAH metabolites, GST and EROD in European eel (Anguilla anguilla) as possible indicators for eel habitat quality in German rivers

The stock of the European eel (Anguilla anguilla L.) continues to decline and has reached a new minimum in 2011. Poor health status of the spawners due to organic contaminants is one of the possible causes for this dramatic situation. Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous contaminants, which are rapidly metabolized in vertebrates. EROD (ethoxyresorufin-O-deethylase) and GST (glutathione-S-transferase) are two enzymes involved in PAH detoxification in fish. In this study, PAH metabolites as well as EROD and GST activity in a large, comprising dataset of more than 260 migratory and pre-migratory eels from five large German river basin districts were used to describe PAH exposure and its metabolism as possible indicators for the habitat quality for eels. Eel from the river Elbe appear to be moderately contaminated with PAH. Highest mean values of PAH metabolites were analysed in fish from the river Rhine. However, the results suggest that contaminants such as PAH are metabolized in the fish and may have contributed to EROD activity in eels caught from the Elbe estuary to 600 km upstream. Since the eel's onset of cessation of feeding is closely linked to maturation and migration, we propose bile pigments as new indicators contributing to identify the proportion of migratory eel, which is crucial information for eel management plans. We showed that PAH metabolites normalized to bile pigments as well as EROD could be used to describe the habitat quality and might be suitable parameters in search for suitable stocking habitats.

Physiological and molecular biochemical mechanisms of bile formation

This review considers the physiological and molecular biochemical mechanisms of bile formation. The composition of bile and structure of a bile canaliculus, biosynthesis and conjugation of bile acids, bile phospholipids, formation of bile micellar structures, and enterohepatic circulation of bile acids are described. In general, the review focuses on the molecular physiology of the transporting systems of the hepatocyte sinusoidal and apical membranes. Knowledge of physiological and biochemical basis of bile formation has implications for understanding the mechanisms of development of pathological processes, associated with diseases of the liver and biliary tract.

The genetic background of gallstone formation: an update

Gallstone disease is one of the most prevalent gastrointestinal diseases with a substantial burden to health care systems that is expected to increase in ageing populations at risk. This review summarizes recent data on the genetic background of cholesterol gallstones and the role of biliary lipid composition. Three previously unknown non-synonymous mutations in the ABCB4 gene encoding the hepatobiliary phospholipid-flippase MDR3 are presented.

[Relationship between pigment gallstone and intestinal barrier function: experiment with guinea pigs and clinical observations]

OBJECTIVE

To investigate the relationship between the intestinal barrier function and pigment gallstone formation.

METHODS

Ninety Guinea pigs were divided randomly into 3 groups: normal control (CON) group receiving normal forage, pigment gallstone (PS) group receiving pigment gallstone-forming forage, and intestinal mucosa protection group receiving pigment gallstone-forming forage with supplemental glutamine intestinal (GLN), a mucosa protector. The guinea pigs were observed for 8 weeks, the gallstone-forming rate, plasma diamine oxidase ( DAO), serum endotoxin, proportionality of urine lactulose/mannitol, and biliary beta-glucuronidase were detected. PCR was used to detect the bacteria in abdominal lymph node taking 16SrRNA as the target gene common in most bacteria. 32 gallstone patients, 16 with cholesterol gallstone and 16 with pigmental gallstone, and 27 patients with non-gastroenterological diseases, as controls, underwent detection of the plasma DAO and serum endotoxin. Another 109 gallstone patients, 31 with cholesterol gallstone and 78 with pigmental gallstone, and 21 patients with nongastroenterological diseases, as controls, underwent detection of urine technetium-labeled diethylenetriamine-pentaacetate (99mTc-DTPA).

RESULTS

The gallstone-forming rate of the guinea pigs of the GLN group was 44.4% was, significantly lower than that of the PS group (73.9%, P < 0.05). The plasma DAO, serum endotoxin levels, proportionality of urine lactulose/mannitol, and activity of biliary beta-glucuronidase of the PS group were all significantly higher than those of the CON group (P < 0.05 or P < 0.01). The plasma endotoxin level of the pigmental GLN group was significantly lower than that of the PS group (P < 0.01). The positive rate of bacteria in abdominal lymph node of the PS group was 80%, significantly higher than those of the CON and GLN groups (30% and 45% respectively, P < 0.01 and P < 0.05). The level of plasma DAO and endotoxin of the pigmental gallstone patients were significantly higher than those of the controls (P < 0.05 and P < 0.01). The urine 99mTc-DTPA excretion rate of gallstone patients was 11.4%, significantly higher than that of the controls (4.7%, P < 0.01).

CONCLUSION

Intestinal barrier function is correlated with pigment gallstone forming. Intestinal barrier function disorder may promote pigment gallstone formation through bacteria translocation, endotoxemia, and increase of biliary beta-glucuronidase.

The anti-mutagenic properties of bile pigments

Bile pigments, including bilirubin and biliverdin, are endogenous compounds belonging to the porphyrin family of molecules. In the past, bile pigments and bilirubin in particular were thought of as useless by-products of heme catabolism that can be toxic if they accumulate. However, in the past 20 years, research probing the physiological relevance of bile pigments has been mounting, with evidence to suggest bile pigments possess significant antioxidant and anti-mutagenic properties. More specifically, bile pigments are potent peroxyl radical scavengers and inhibit the mutagenic effects of a number of classes of mutagens (polycyclic aromatic hydrocarbons, heterocyclic amines, oxidants). Coincidentally, persons with elevated circulating bilirubin concentrations have a reduced prevalence of cancer and cardio-vascular disease. Despite the encouraging in vitro anti-mutagenic effects of bile pigments, relatively little research has been conducted on their inhibitory capacity in bacterial and cultured cell assays of mutation, which might link the existing in vitro and in vivo observations. This is the first review to summarise the published data and it is our hope it will stimulate further research on these potentially preventative compounds.

Gallbladder inflammation is associated with increase in mucin expression and pigmented stone formation

Mucin is a high molecular weight glycoprotein that plays an important role in protecting the gallbladder epithelium from the detergent effect of bile. However, it also participates in gallstone formation. There is little information about a possible relationship between gallbladder inflammation and mucin expression or gallbladder stones' characteristics. The aims of this study were to investigate stone characteristics and patterns of mucin expression in the gallbladder epithelium and bile of gallstone patients, in relation to inflammation. Gallbladder bile and tissue samples from 21 patients were obtained at surgery. Mucin content was evaluated by gel filtration on a Sepharose CL-4B column. Dot blot for bile mucin apoproteins and immunohistochemistry staining for gallbladder mucosal mucin apoproteins were performed with antibodies to MUC2, MUC3, MUC5AC, MUC5B and MUC6. Staining intensity score (0-3) was used for assessment of antigen expression and the level of inflammation. Gallstone cholesterol content was determined in 16 patients. MUC 5AC and MUC 5B were demonstrated in 95.4 and 100% of gallbladder bile samples, respectively. Immunohistochemistry staining with antibodies to MUC 2, MUC 3, MUC 5AC, MUC 5B and MUC 6 were positive in 0, 100, 85.7, 100 and 95.4% of the gallbladder mucosal samples, respectively. Pigmented brown stones were associated with a higher level of gallbladder inflammation. Mucin species expressed in gallbladder epithelium are MUC3, MUC5AC, MUC5B and MUC6. MUC5AC and MUC5B are secreted into bile. Inflammation of the gallbladder is accompanied by a higher level of MUC5AC expression and is associated with pigmented brown stones.

Light-independent phytochrome signaling mediated by dominant GAF domain tyrosine mutants of Arabidopsis phytochromes in transgenic plants

The photoreversibility of plant phytochromes enables continuous surveillance of the ambient light environment. Through expression of profluorescent, photoinsensitive Tyr-to-His mutant alleles of Arabidopsis thaliana phytochrome B (PHYB(Y276H)) and Arabidopsis phytochrome A (PHYA(Y242H)) in transgenic Arabidopsis plants, we demonstrate that photoconversion is not a prerequisite for phytochrome signaling. PHYB(Y276H)-expressing plants exhibit chromophore-dependent constitutive photomorphogenesis, light-independent phyB(Y276H) nuclear localization, constitutive activation of genes normally repressed in darkness, and light-insensitive seed germination. Fluence rate analyses of transgenic plants expressing PHYB(Y276H), PHYA(Y242H), and other Y(GAF) mutant alleles of PHYB demonstrate that a range of altered light-signaling activities are associated with mutation of this residue. We conclude that the universally conserved GAF domain Tyr residue, with which the bilin chromophore is intimately associated, performs a critical role in coupling light perception to signal transduction by plant phytochromes.

Role of caveolae in the pathogenesis of cholesterol-induced gallbladder muscle hypomotility

Muscle cells from human gallbladders (GB) with cholesterol stones (ChS) exhibit a defective contraction, excess cholesterol (Ch) in the plasma membrane, and lower binding of CCK-1 receptors. These abnormalities improved after muscle cells were incubated with Ch-free liposomes that remove the excess Ch from the plasma membrane. The present studies were designed to investigate the role of caveolin-3 proteins (Cav-3) in the pathogenesis of these abnormalities. Muscle cells from GB with ChS exhibit higher Ch levels in the plasma membrane that were mostly localized in caveolae and associated with parallel increases in the expression of Cav-3 in the caveolae compared with that in GB with pigment stones (PS). The overall number of CCK-1 receptors in the plasma membrane was not different between muscle cells from GB with ChS and PS, but they were increased in the caveolae in muscle cells from GB with ChS. Treatment of muscle cells from GB with ChS with a Galpha(i3) protein fragment increased the total binding of CCK-1 receptors (from 8.3 to 11.2%) and muscle contraction induced by CCK-8 (from 11.2 to 17.3% shortening). However, Galpha(q/11) protein fragment had no such effect. Moreover, neither fragment had any effect on muscle cells from GB with PS. We conclude that the defective contraction of muscle cells with excessive Ch levels in the plasma membrane is due to an increased expression of Cav-3 that results in the sequestration of CCK-1 receptors in the caveolae, probably by inhibiting the functions of Galpha(i3) proteins.

[Effect of clearing heat and removing dampness method on formation of pigment gallstones in rabbits]

OBJECTIVE

To observe dynamically the effect of drugs for clearing heat and removing dampness (CHRD) on biliary components in rabbits with pigment gallstones (PGS).

METHODS

Forty rabbits were established into PGS model and randomly divided into 3 groups, the bacterial infection group, the CHRD low-dose group and the CHRD high-dose group. Besides, a normal group was set up with healthy rabbits for control. Changes of total bilirubin (TB), unconjugated bilirubin (UCB), total bile acid (TBA), Ca2+, bacterial and endogenous beta-glucuronidase (beta-Gase) in bile were observed.

RESULTS

CHRD drugs significantly decreased the contents of UCB, Ca2+, bacterial and endogenous beta-Gase (P < 0.05), and increased TBA in bile (P < 0.05).

CONCLUSION

CHRD drugs have good effect in reducing the lithogenesis of the pigment gallstones.

[The relationship between Oddi's sphincter and bile duct pigment gallstone]

OBJECTIVE

To investigate the relationship between anatomic abnormalities and malfunction of Oddi sphincter with formation of bile duct pigment gallstone.

METHODS

One hundred and twenty-three patients with a T tube after cholecystectomy and choledochotomy were divided into reflux group and control group by measuring the amounts of radioactivity of (99m)Tc-DTPA in the bile. Among them 53 were selected randomly to undergo choledochoscopic manometry. Basal pressure of Oddi's sphincter (SOBP), amplitude of Oddi's sphincter (SOCA), frequency of contraction (SOF), duration of contraction (SOD), duodenal pressure (DP), common bile duct pressure (CBDP) were scored and analyzed. The level of plasma motilin and serum gastrin of 45 patients and 12 healthy volunteers were measured by radioimmunoassay. The incidence rates of duodenal descending part diverticulum in patients with bile duct pigment stones, patients without alimentary tract diseases, patients with gallbladder polyps, patients with gallbladder stones were studied by means of barium meal examination. The incidence rates of intraduodenal peri-ampullary diverticulum in patients with primary bile duct pigment stones, patients with bile duct stone and gallbladder stones, patients with bile duct stones originating from the gallbladder, patients with inflammation and stricture of the extremity of bile duct and papilla, patients with cancer of the extremity of bile duct and papilla, patients with post-cholecystectomy syndrome were detected by duodenoscope.

RESULTS

Of the patients, 44 were detected with duodenal-biliary reflux (35.8%). SOBP, SOCA and CBDP in the reflux group were much lower than those in control group (P < 0.001). The level of serum gastrin and plasma motilin of the reflux group were much lower than those of control group (P < 0.01). Positive correlation was found between level of motilin and SOBP while level of gastrin was positively correlated with SOBP and CBDP. The incidence of duodenal diverticulum in patients with bile duct pigment stone was 36.62%, which was higher than that of the other 3 groups. The incidence rate of intraduodenal peri-ampullary diverticulum in patients with primary bile duct pigment stone was higher than that of patients with inflammation and stricture of the extremity of bile duct and papilla, patients with cancer of the extremity of bile duct and papilla and patients with bile duct stones originating from the gallbladder.

CONCLUSIONS

The patients with bile duct pigment stone have apparent duodenal-biliary reflux and infection of the bile duct. The state of structure and function of Oddi's sphincter is correlated significantly with bile duct pigment stone. The anatomic abnormalities and malfunction of Oddi's sphincter played an important role in the formation of bile duct pigment stone.

Characterization of a major secretory protein in the cane toad (Bufo marinus) choroid plexus as an amphibian lipocalin-type prostaglandin D synthase

Here we report the enzymatic and ligand-binding properties of a major secretory protein in the choroid plexus of cane toad, Bufo marinus, whose protein is homologous with lipocalin-type prostaglandin (PG) D synthase (L-PGDS) and is recombinantly expressed in Xenopus A6 cells and Escherichia coli. The toad protein bound all-trans retinal, bile pigment, and thyroid hormones with high affinities (K(d)=0.17 to 2.00 microM). The toad protein also catalysed the L-PGDS activity, which was accelerated in the presence of GSH or DTT, similar to the mammalian enzyme. The K(m) value for PGH(2) (17 microM) of the toad protein was almost the same as that of rat L-PGDS (14 microM), whereas the turnover number (6 min(-1)) was approximately 28 fold lower than that of rat L-PGDS. Site-directed mutagenesis based on a modeled structure of the toad protein revealed that Cys(59) and Thr(61) residues were crucial for the PGDS activity. The quadruple Gly(39)Ser/Ala(75)Ser/Ser(140)Thr/Phe(142)Tyr mutant of the toad protein, resembling mouse L-PGDS, showed a 1.6 fold increase in the turnover number and a shift in the optimum pH for the PGDS activity from 9.0 to 8.5. Our results suggest that the toad protein is a prototype of L-PGDS with a highly functional ligand-binding pocket and yet with a primitive catalytic pocket.

[Effects of Shengqing Capsules on expression of nuclear factor-kappaB protein in liver cells of guinea pigs with pigment gallstone]

OBJECTIVE

To study the mechanisms of Shengqing Capsules, a compound Chinese herbal medicine for dispersing stagnated liver qi and promoting bile flow, in prevention and treatment of pigment gallstone.

METHODS

Liver cells from guinea pigs with pigment gallstone were primarily cultured in vitro. The serums containing different concentrations of Shengqing Capsules were prepared by serum pharmacological method. The primary cultured hepatocytes with excessive expression of nuclear factor-kappaB (NF-kappaB) were stimulated with lipopolysaccharides (LPS) and the effects of the drug-containing serums on the NF-kappaB expression were detected by Western-blotting.

RESULTS

Shengqing Capsules down-regulated the NF-kappaB expression increased by LPS stimulation. The effect is dose-dependent.

CONCLUSION

Shengqing Capsules can down-regulate the NF-kappaB expression increased by LPS stimulation. It may be one of the important mechanisms of this Chinese herbal medicine in prevention and treatment for pigment gallstone formation and the inflammatory reaction in biliary tract.

Biosynthesis of fluorescent allophycocyanin alpha-subunits by autocatalytic bilin attachment

Allophycocyanin (APC) is one of the phycobiliproteins expressed in cyanobacteria. Phycobiliproteins contain a covalently bound chromophore, and thus, they are valuable as fluorescent probes. Biosynthesis of a functional phycobiliprotein is achieved by a bilin attachment process between the chromophore and apoprotein. Chromophore lyases are necessary to catalyze the chromophorylation of cyanobacterial phycobiliproteins, such as C-phycocyanin, and phycoerythrocyanin. To identify the lyase that catalyzes the chromophorylation of the APC alpha-subunit (ApcA), we searched the entire genomes of two cyanobacteria, Synechocystis sp. PCC6803 and Anabaena sp. PCC 7120; however, these genomes do not appear to encode an APC-specific chromophore lyase. In this study, chromophorylated ApcA (chromo-ApcA) was obtained via a spontaneous bilin attachment reaction. The absorption and fluorescence characteristics of chromo-ApcA were similar to those of the native APC alpha-subunit. The extent of chromophore attachment to apo-ApcA was comparable to that of the lyase-catalyzed reactions for other phycobiliproteins. These results indicate that ApcA has autocatalytic bilin:biliprotein lyase activity.

Reconstitution of blue-green reversible photoconversion of a cyanobacterial photoreceptor, PixJ1, in phycocyanobilin-producing Escherichia coli

PixJ1, a photoreceptor in the unicellular cyanobacterium Synechocystis sp. PCC 6803, mediates positive phototactic motility and contains two GAF domains, the latter of which binds a bilin chromophore. Full-length PixJ1 expressed and purified from Synechocystis showed unique reversible photoconversion between a blue light-absorbing (Pb) form and a green light-absorbing (Pg) form (1) in contrast to the reversible phototransformation between the red light-absorbing form and far-red light-absorbing form of the other GAF-containing photoreceptors such as plant or bacterial phytochromes. To clarify the origin of the blue-shifted photoconversion, we tried to reconstitute this blue-green reversible phototransformation by synthesizing the second GAF domain in Escherichia coli transformed with genes for biosynthesis of four different bilins, biliverdin (BV), bilirubin (BR), phycocyanobilin (PCB), and phycocyanorubin (PCR), as final products. The three expression systems, the BR system being the exception, produced a GAF polypeptide with a covalently bound bilin. The GAF polypeptide from the BV-synthesizing system exhibited an irreversible photoconversion, while that from the PCB-synthesizing system revealed photoconversion between Pb and Pg almost identical to that of the full-length PixJ1, indicating that PCB is responsible for the blue-green reversible photoconversion. Furthermore, the GAF polypeptide from the PCR-producing system exhibited almost the same reversible spectral change, possibly coming from the PCB accumulated in the PCR-biosynthetic pathway. Mass spectrometry (MS) of the main tryptic chromopeptide revealed that the chromophore binds to a 21-amino acid peptide that contains a cysteine-histidine motif for phytochrome chromophore binding and that an ion signal can be assigned to desorbed PCB. The absorption spectra of the denatured GAF polypeptide suggested that PCB is attached to the protein moiety in a twisted conformation that disrupts the pi-electron conjugation between the A and B rings, possibly being held in position through a second covalent linkage.

[The activity of gastrointestinal enzymes in chronic viral hepatitis B and C]

The study was undertaken to evaluate the enzymatic activity of the gastrointestinal tract in patients with chronic viral hepatitis (CVH) B and C. Fecal tests were made in 44 patients. The general pancreatic maldigestion syndrome was observed in 18% of patients with CVH B and C. A direct relationship was found between the content of starch, and indigested muscle fibers, neutral fat, and digested cellulose, which points to the fact that there is a decrease in the pancreatic acinous tissue synthesis of just several enzymes, i.e. generalized pancreatic insufficiency was observed. It is recommended that all patients with CVH should undergo a fecal test whereby the enzymatic activity of the gastrointestinal tract may be, if a certain diet is given, evaluated to prescribe timely enzyme replacement therapy.

A light-sensing knot revealed by the structure of the chromophore-binding domain of phytochrome

Phytochromes are red/far-red light photoreceptors that direct photosensory responses across the bacterial, fungal and plant kingdoms. These include photosynthetic potential and pigmentation in bacteria as well as chloroplast development and photomorphogenesis in plants. Phytochromes consist of an amino-terminal region that covalently binds a single bilin chromophore, followed by a carboxy-terminal dimerization domain that often transmits the light signal through a histidine kinase relay. Here we describe the three-dimensional structure of the chromophore-binding domain of Deinococcus radiodurans phytochrome assembled with its chromophore biliverdin in the Pr ground state. Our model, refined to 2.5 A resolution, reaffirms Cys 24 as the chromophore attachment site, locates key amino acids that form a solvent-shielded bilin-binding pocket, and reveals an unusually formed deep trefoil knot that stabilizes this region. The structure provides the first three-dimensional glimpse into the photochromic behaviour of these photoreceptors and helps to explain the evolution of higher plant phytochromes from prokaryotic precursors.

Molecular bases of the excretion of fetal bile acids and pigments through the fetal liver-placenta-maternal liver pathway

Since the excretion of potentially toxic cholephilic organic anions (COAs) produced by the fetus, such as bile acids and biliary pigments, cannot be performed by the fetal liver alone, the placenta and the maternal liver must play a key role collaborating in this function. COAs are transported across the plasma membranes of fetal and maternal hepatocytes and trophoblastic cells via similar carrier proteins. OATPs (organic anion-transporting polypeptides), mainly OATP1B1 and OATP1B3 are involved in COA uptake across the basal membrane of adult hepatocytes and trophoblastic cells. Certain OATPs may also play a role in COA efflux from fetal hepatocytes toward the fetal blood and from the trophoblast to the maternal blood. Either unmodified or biotransformed during their transit across the placenta, COAs are transferred to the maternal blood by MRPs (multidrug resistance-associated proteins), such as MRP1, MRP2 and MRP3. BCRP (breast cancer resistance protein) may also be involved in this step. Under physiological circumstances, fetal COAs are taken up by the maternal liver, which eliminates them across the canalicular membrane via MRP2 and BSEP (bile salt export pump). However, when normal biliary excretion is not possible, the accumulation of COAs, in particular in the fetal liver, placenta and maternal liver trio, induces oxidative stress and apoptosis, which has noxious repercussions on normal fetal development and even challenges pregnancy outcome. Treatment of pregnant rats with ursodeoxycholic acid, even though maternal hypercholanemia is not corrected, prevents oxidative damage and the subsequent deleterious effects on the placenta and fetal liver.

Effect of Capsaicin on Bile Secretion in the Rat

Capsaicin is a popular food ingredient. This study aimed to determine if capsaicin can affect bile flow and bile protein secretion, and the extent to which capsaicin can reach bile in the rat. The effect of capsaicin was studied in anesthetized rats equipped with cannulas inserted into the common bile duct. Capsaicin was administered by intragastric, intraduodenal (4-400 microg/ml; 10-1,000 microg/kg), intravenous (10 microg/kg) routes or applied on the serosal surface of the duodenum at 4 microg/ml. The administration of capsaicin decreased bile flow in comparison to the corresponding basal values, the maximum effect being reached at a concentration of 400 microg/ml of intragastric capsaicin (30.2%; p < 0.01), and 40 microg/ml (30.8%; p < 0.01) of intraduodenal capsaicin, 75 min after drug administration. Meanwhile, a decrease of 24.7 and 40% was observed 60 min after serosal and intravenous capsaicin administration, respectively. Biliary protein secretion was also reduced following capsaicin administration. High-performance liquid chromatography (HPLC) analysis showed that capsaicin was readily excreted into bile, peak levels were reached 75 or 60 min following its intragastric or intraduodenal administration, respectively (range 100-248 and 144-698.6 ng/ml after intragastric or intraduodenal capsaicin at 4-400 microg/ml, respectively). Capsaicin concentrations of 86 and 75 ng/ml could be detected in bile 15 min after intravenous administration or serosal application of the agent, respectively. Results suggest that capsaicin is readily absorbed after its intragastric or intraduodenal administration and goes through hepatobiliary excretion. Results also indicate that administration of capsaicin reduces bile flow and biliary proteins in the rat.

Generation of bile pigments by haem oxygenase: a refined cellular strategy in response to stressful insults

The family of haem oxygenase enzymes is unique in nature for its role in haem degradation. Haem is cleaved at the α-meso position by haem oxygenase with the support of electrons donated by cytochrome P450 reductase, the first products of this reaction being CO, iron and biliverdin. Biliverdin is then converted to bilirubin by biliverdin reductase. If haem is viewed as a substrate for an anabolic pathway, it becomes evident that haem oxygenases do not break down haem for elimination from the body, but rather use haem to generate crucial molecules that can modulate cellular functions. The facts that biliverdin and bilirubin are potent antioxidants and that CO is both a vasoactive and signalling molecule sustain this idea. The existence of a constitutive haem oxygenase (HO-2), mainly present in the vasculature and nervous system, and an inducible haem oxygenase (HO-1), which is highly expressed during stress conditions in all tissues, also suggests that cells have evolved a fine control of this enzymic pathway to ultimately regulate haem consumption and to ensure production of CO, biliverdin/bilirubin and iron during physiological and pathophysiological situations. This review will focus primarily on the biological actions of biliverdin and bilirubin derived from the haem oxygenase/biliverdin reductase systems and their potential roles in counteracting oxidative and nitrosative stress.

Inhibition of cholesterol crystallization under bilirubin deconjugation: partial characterization of mechanisms whereby infected bile accelerates pigment stone formation

Pigment gallstones have been reported to be closely associated with biliary tract infection. We previously reported that addition of unconjugated bilirubin (UCB), which is deconjugated by beta-glucuronidase in infected bile, could enhance cholesterol crystal formation in supersaturated model bile (MB). The present study evaluated the effect of beta-glucuronidase on the processes of pigment gallstone formation and cholesterol crystallization. Supersaturated MB (taurocholate/lecithin/cholesterol at 71:18:11, a total lipid concentration of 10.0 g/dl and a cholesterol saturation index (CSI) of 2.0) and native rat bile were mixed at a ratio of 3:1. Then, mixed bile was incubated with or without beta-glucuronidase and changes of the following parameters were investigated over time: (1) the UCB/total bilirubin ratio; (2) cholesterol crystal formation; (3) the precipitate weight and the cholesterol concentration in the precipitate and supernatant; and (4) the lipid distribution of vesicles in the supernatant. Compared with beta-glucuronidase-free bile, (1) beta-glucuronidase-containing bile showed a significant increase of the UCB/total bilirubin ratio, (2) as well as a significantly longer nucleation time (96+/-17.0 vs. 114+/-20.0) and fewer cholesterol crystals. (3) The precipitate weight and the cholesterol concentration in the precipitate were significantly increased, while the cholesterol concentration in supernatant was decreased. (4) When mixed bile was incubated with beta-glucuronidase, the cholesterol concentration in the vesicles was lower than in bile without beta-glucuronidase. The precipitate weight and the cholesterol concentration in the precipitate was increased by incubation with beta-glucuronidase, while cholesterol concentration was decreased in the supernatant (especially in the vesicles). This means that bile vesicles were more stable and it was more difficult for cholesterol crystals to form. Thus, the presence of beta-glucuronidase may inhibit the formation of pure cholesterol stones even in the presence of cholesterol supersaturation.

Biochemical properties of CikA, an unusual phytochrome-like histidine protein kinase that resets the circadian clock in Synechococcus elongatus PCC 7942

We recently described the cikA (circadian input kinase A) gene, whose product supplies environmental information to the circadian oscillator in the cyanobacterium Synechococcus elongatus PCC 7942. CikA possesses three distinct domains: a GAF, a histidine protein kinase (HPK), and a receiver domain similar to those of the response regulator family. To determine how CikA functions in providing circadian input, we constructed modified alleles to tag and truncate the protein, allowing analysis of each domain individually. CikA covalently bound bilin chromophores in vitro, even though it lacks the expected ligand residues, and the GAF domain influenced but did not entirely account for this function. Full-length CikA and truncated variants that carry the HPK domain showed autophosphorylation activity. Deletion of the GAF domain or the N-terminal region adjacent to GAF dramatically reduced autophosphorylation, whereas elimination of the receiver domain increased activity 10-fold. Assays to test phosphorelay from the HPK to the cryptic receiver domain, which lacks the conserved aspartyl residue that serves as a phosphoryl acceptor in response regulators, were negative. We propose that the cryptic receiver is a regulatory domain that interacts with an unknown protein partner to modulate the autokinase activity of CikA but does not work as bona fide receiver domain in a phosphorelay.

The hepatobiliary-like excretory function of the placenta. A review

In the adult, several endogenous compounds, such as bile acids and biliary pigments, as well as many xenobiotics are mainly biotransformed and eliminated by the hepatobiliary system. However, because this function is immature in the foetus, this role is carried out by the placenta during the intrauterine life. This review describes current knowledge of the trophoblastic machinery responsible for this function, which includes transport and metabolic processes, similar in part to those existing in the mature liver. Because many of the studies reviewed here were conducted on human or rat near-term placentae, two aspects should be borne in mind: (i) although both types of placenta are haemochorial, profound species-specific differences at the structural, molecular and functional levels do exist, and (ii) the placenta is an organ undergoing continuous developmental changes, including its hepatobiliary-like excretory function.

Carbon monoxide and bile pigments: surprising mediators of vascular function

Heme oxygenase (HO) catalyzes the degradation of heme to CO, iron, and biliverdin. Biliverdin is subsequently metabolized to bilirubin by the enzyme biliverdin reductase. Although long considered irrelevant byproducts of heme catabolism, recent studies indicate that CO and the bile pigments biliverdin and bilirubin may play an important physiological role in the circulation. The release of CO by vascular cells may modulate blood flow and blood fluidity by inhibiting vasomotor tone, smooth muscle cell proliferation, and platelet aggregation. CO may also maintain the integrity of the vessel wall by directly blocking vascular cell apoptosis and by inhibiting the release of pro-apoptotic inflammatory cytokines from the vessel wall. These effects of CO are mediated via multiple pathways, including activation of soluble guanylate cyclase, potassium channels, p38 mitogen-activated protein kinase, or inhibition of cytochrome P450. In addition, the release of bile pigments may serve to sustain vascular homeostasis by protecting vascular cells from oxidative stress and by inhibiting the adhesion and infiltration of leukocytes into the vessel wall. Induction of HO-1 gene expression and the subsequent release of CO and bile pigments are observed in numerous vascular disorders and may provide an important adaptive mechanism to preserve homeostasis at sites of vascular injury. Thus, the HO-catalyzed formation of CO and bile pigments by vascular cells may function as a critical endogenous vasoprotective system. Moreover, pharmacological or genetic approaches targeting HO-1 to the vessel wall may represent a novel therapeutic approach in treating vascular disease.

Phytochrome ancestry: sensors of bilins and light

Phytochromes were long thought to have evolved in non-motile photosynthetic eukaryotes for adaptation to unfavorable light environments, but recent studies suggest that phytochromes evolved billions of years earlier from a tetrapyrrole sensor protein progenitor. These investigations have identified phytochromes and phytochrome-related proteins in photosynthetic bacteria (cyanobacteria and purple bacteria), nonphotosynthetic eubacteria and fungi - an observation that has opened new avenues for investigating the origins, molecular evolution and biochemical functions of this ecologically important family of plant photoreceptors.

Bilirubin/biliverdin-Cu(II) induced DNA breakage; reaction mechanism and biological significance

Bilirubin and its metabolic precursor biliverdin are heme degradation products but have been proposed as physiological antioxidants. Reports from another laboratory as well as from ours have shown bilirubin to form a complex with the transition metal ion-Cu(II). Such a complex was shown by us to cause oxidative DNA damage. Further, biliverdin was also shown to be capable of causing similar DNA damage. In the present studies we have aimed to elucidate the mechanism of DNA breakage reaction by these bile pigments. Absorption and fluorescence studies indicate binding of bile pigments to DNA and copper ions. Cu(II) is reduced by these compounds to Cu(I) which is an essential intermediate in the DNA breakage reaction. Redox recycling of Cu(II) leads to generation of reactive oxygen species. Strand scission by the bile pigments-Cu(II) system is found to be biologically significant as assayed by bacteriophage inactivation. Our results, therefore are suggestive of one of the mechanisms through which endogenous DNA damage may occur.

Regioselective oxidative liberation of aryl-substituted tripyrrinone metal complexes from N-confused porphyrin

[reaction: see text] A Cu(II) complex of the first aryl-substituted tripyrrinone derivative, 14-benzoyl-5,10-diphenyl-1-oxo-tripyrrinato copper(II) (3-Cu) was obtained in the reaction of N-confused tetraphenylporphyrin (NCTPP) and Cu(OAc)(2) in refluxing toluene, and subsequent treatment with acid afforded a free tripyrrolic ligand that could bind a variety of transition metals.

Does bilirubin play a role in the pathogenesis of both cholesterol and pigment gallstone formation? Direct and indirect influences of bilirubin on bile lithogenicity

Bilirubin is found in the center of cholesterol gallstones, but its pathogenic role in their formation is unknown. Bilirubin causes a disproportionate reduction of biliary lipid secretion without affecting bile salt secretion in association with a change of biliary lecithin species, which modulates the cholesterol crystallization process. Therefore, the present study investigated whether bilirubin can influence the cholesterol crystallization procedure, and the mechanism(s) of any such action. Supersaturated model bile was prepared (taurocholate/lecithin/cholesterol at 71:18:11, a total lipid concentration of 9.0 g/dl, and cholesterol saturation index of 1.8), and cholesterol crystallization was monitored over time using a spectrophotometer and video-enhanced differential contrast microscopy in the absence or presence of bilirubin (at a final concentration of 10 microM, 20 microM, 40 microM, and 100 microM). Bilirubin enhanced the onset of cholesterol crystallization by 50%, whereas the crystal growth rate and final crystal mass were reduced at a high concentration of bilirubin. Taken together, these results suggest that bilirubin influences the cholesterol crystallization process, by either a direct interaction with biliary lipids that alters metastability, an indirect alteration of the bile salt-micellar lipid holding capacity, or both. Thus, bilirubin may play a role in the pathogenesis of both cholesterol and pigment gallstones.

Defining the bilin lyase domain: lessons from the extended phytochrome superfamily

Through pattern searches of genomic databases, new members of the growing family of phytochrome-related genes were identified and used to construct a 130-180 amino acid motif that delimits the bilin lyase domain, a subdomain of the extended phytochrome family that is sufficient for covalent attachment of linear tetrapyrroles (bilins). To test this hypothesis, portions of locus sll0821, a novel phytochrome-related gene from Synechocystis sp. PCC6803 that encodes a large protein with two potential bilin binding sites, were amplified, and the recombinant apoproteins were tested for bilin binding and phytochrome photoactivity. Our experiments indicated that both sites of this protein, termed Cph2 for cyanobacterial phytochrome 2, possessed bilin lyase activity, revealing two distinct classes of bilin lyase domains--those whose bilin adducts are red, far-red reversible and a second class whose bilin adducts are nonphotochromic. Spectroscopic analysis of photochromic phycocyanobilin and fluorescent phycoerythrobilin adducts of a 24-kDa fragment of Cph2 definitively established that the motif identified by pattern searches represents a bona fide bilin lyase domain. Site-directed mutagenesis of highly conserved charged residues within bilin lyase domains of nearly all members of the extended phytochrome superfamily has identified a glutamate residue critical for bilin binding.

Melatonin prevents pigment gallstone formation induced by bile duct ligation in guinea pigs

Free radical-mediated oxidative stress has been implicated in the genesis of gallstone in vitro. This study was designed to examine the oxidative stress changes during pigment gallstone formation and to investigate whether melatonin (MLT) could act as a chemopreventive agent for cholelithiasis in a guinea pig model. The common bile duct of guinea pigs was ligated with or without MLT pretreatment. Animals were studied on day 7, 9, 12, and 14 after surgery. Stone and/or sludge developed in ligated guinea pigs without MLT. Fourier transform infrared spectra of the sludge showed the presence of calcium bilirubinate, whose peak height per milligram of sludge gradually increased with time after ligation. Total antioxidant activity (TAA) in bile of guinea pigs at day 14 after ligation reduced to one third of the level in sham-operated controls (P <.001). In addition, the bile of ligated guinea pigs had increased pH (P <.001), bile salts (P <.01), and malondialdehyde (MDA) (P <.05), compared to sham controls. Pretreatment of guinea pigs with MLT at a dose of 1,000 microg/kg significantly decreased the incidence of pigment gallstone formation at day 14 after ligation, as compared to no pretreatment (0/7 vs. 8/10). MLT also reverted the ligation-induced changes in biliary bile salts, pH, MDA, and TAA to control levels. These in vivo findings support a causative role of oxidative stress in the bile duct ligation-induced pigment gallstone formation. Antioxidants may prove useful in preventing pigment gallstone formation in humans.