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C Funk

Publications and source records attributed to C Funk.

At least 19 recordsLinked to original sources
PubMed2001

Troglitazone-induced intrahepatic cholestasis by an interference with the hepatobiliary export of bile acids in male and female rats. Correlation with the gender difference in troglitazone sulfate formation and the inhibition of the canalicular bile salt export pump (Bsep) by troglitazone and troglitazone sulfate.

Troglitazone is a thiazolidinedione insulin sensitizer drug for the treatment of type 2 non-insulin-dependent diabetes mellitus (NIDDM). Based on an increasing number of reports on troglitazone-associated liver toxicity, the cholestatic potential of troglitazone and its major metabolite troglitazone sulfate has been investigated. In isolated perfused rat livers troglitazone (10 microM) reduced the bile flow by 25% (female) to 50% (male) within 60 min. After single intravenous administrations of troglitazone to rats of both genders, rapid and dose-dependent increases in the plasma bile acid concentrations were observed, with male rats being more sensitive than female rats. In male rat liver tissue fivefold higher troglitazone sulfate levels were measured as compared to female rat liver tissue. This difference was due to the formation rate of troglitazone sulfate, which was four times faster in cytosolic fractions of male rat liver as compared to female rat liver (Clint=132 and 35 microl min(-1) mg(-1), respectively). Troglitazone sulfate strongly inhibited the ATP-dependent taurocholate transport mediated by the canalicular bile salt export pump (Bsep) in isolated canalicular rat liver plasma membrane preparations of both genders (IC(50) value of 0.4-0.6 microM), while troglitazone was 10 times less potent (IC(50) values of 3.9 microM). This high Bsep inhibition potential and the efficient formation and accumulation of troglitazone sulfate in liver tissue, suggested that troglitazone sulfate was mainly responsible for the interaction with the hepatobiliary export of bile acids at the level of the canalicular Bsep in rats. Such an interaction might lead potentially also in man to a troglitazone-induced intrahepatic cholestasis, potentially contributing to the formation of troglitazone-induced liver injuries.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2001

D1' centers are less efficient than normal photosystem II centers.

One prominent difference between the photosystem II (PSII) reaction center protein D1' in Synechocystis 6803 and normal D1 is the replacement of Phe-186 in D1 with leucine in D1'. Mutants of Synechocystis 6803 producing only D1', or containing engineered D1 proteins with Phe-186 substitutions, were analyzed by 77 K fluorescence emission spectra, chlorophyll a fluorescence induction yield and decay kinetics, and flash-induced oxygen evolution. Compared to D1-containing PSII centers, D1' centers exhibited a 50% reduction in variable chlorophyll a fluorescence yield, while the flash-induced O(2) evolution pattern was unaffected. In the F186 mutants, both the P680(+)/Q(A)(-) recombination and O(2) oscillation pattern were noticeably perturbed.

Amino Acid Substitution↗
PubMed2001

The endothelin antagonist bosentan inhibits the canalicular bile salt export pump: a potential mechanism for hepatic adverse reactions.

BACKGROUND: During clinical trials bosentan, the first orally active endothelin receptor antagonist, caused asymptomatic transaminase elevations in some patients. In this study we investigated whether inhibition of the hepatocanalicular bile salt export pump (rodents, Bsep; humans, BSEP ABCB11) could account for bosentan-induced liver injury. METHODS: We reanalyzed the safety database of the bosentan trials for cholestatic liver injury, determined the cholestatic potency of bosentan in the rat, and studied the effects of bosentan and its metabolites on Bsep-mediated taurocholate transport in vitro. RESULTS: Bosentan caused dose-dependent and reversible liver injury in 2% to 18% of patients and caused a significant increase of serum bile salt levels (P <.01). Concomitant administration of glyburide (INN, glibenclamide) enhanced the cholestatic potency of bosentan. Similar effects were seen in rats, in which serum bile salt levels were increased by glyburide less than by bosentan, which increased the levels less than a combination of bosentan and glyburide. In vitro, Bsep-mediated taurocholate transport was inhibited by bosentan (inhibition constant, approximately 12 micromol/L) and metabolites (inhibition constant, approximately 8.5 micromol/L for metabolite Ro 47-8634). CONCLUSIONS: These results indicate that bosentan-induced liver injury is mediated, at least in part, by inhibition of Bsep/BSEP-causing intracellular accumulation of cytotoxic bile salts and bile salt induced liver cell damage. The data further emphasize the pathophysiologic importance of drug-Bsep interactions in acquired forms of cholestatic liver injury.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2001

Subtotal pedal amputations. Biomechanical and intraoperative considerations.

Proper treatment for the compromised diabetic foot often requires surgical correction and subtotal pedal amputation. This article discusses various levels of amputation of the human foot, including digital, ray, transmetatarsal, midfoot, and Syme amputations. Surgical techniques and biomechanical considerations are presented in order to assist the surgeon in planning for the most functional outcome of the patient. A review of the literature and the experiences of the authors are presented.

Amputation, Surgical↗
PubMed2001

Cholestatic potential of troglitazone as a possible factor contributing to troglitazone-induced hepatotoxicity: in vivo and in vitro interaction at the canalicular bile salt export pump (Bsep) in the rat.

Troglitazone is a thiazolidinedione insulin sensitizer drug for the treatment of type 2 non-insulin-dependent diabetes mellitus (NIDDM). Based on an increasing number of reports on troglitazone-associated liver toxicity, the cholestatic potential of troglitazone has been investigated. Rapid and dose-dependent increases in the plasma bile acid concentrations were observed in rats after a single intravenous administration of troglitazone. A radiolabeled taurocholic acid tracer accumulated in liver tissue, indicating an interference with the hepatobiliary export of bile acids. In isolated canalicular rat liver plasma membrane preparations, troglitazone competitively inhibited the ATP-dependent taurocholate transport (apparent K(i) value, 1.3 microM), mediated by the canalicular bile salt export pump (Bsep). Troglitazone sulfate, the main troglitazone metabolite eliminated into bile, also showed competitive Bsep inhibition with an apparent K(i) value of 0.23 microM. A comparable inhibition was observed for both compounds in canalicular plasma membrane vesicles prepared from Mrp2-deficient (TR(-)) rats, suggesting a direct (cis-) inhibition of Bsep by troglitazone and troglitazone sulfate. A high accumulation potential was observed for troglitazone sulfate in rat liver tissue, indicating that the hepatobiliary export of this conjugated metabolite might represent a rate-limiting step in the overall elimination process of troglitazone. This accumulation in combination with the high Bsep inhibition potential suggested that mainly troglitazone sulfate was responsible for the interaction with the hepatobiliary export of bile acids at the level of the canalicular Bsep in rats. Such an interaction might lead to a troglitazone-induced intrahepatic cholestasis in humans as well, contributing to the formation of a troglitazone-induced liver toxicity.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2000

Supermolecular structure of photosystem II and location of the PsbS protein.

This paper addresses the question of whether the PsbS protein of photosystem two (PS II) is located within the LHC II PS II supercomplex for which a three-dimensional structure has been obtained by cryoelectron microscopy and single particle analysis. The PsbS protein has recently been implicated as the site for non-photochemical quenching. Based both on immunoblotting analyses and structural considerations of an improved model of the spinach LHC II PS II supercomplex, we conclude that the PsbS protein is not located within the supercomplex. Analyses of other fractions resulting from the solubilization of PS Il-enriched membranes derived from spinach suggest that the PsbS protein is located in the LHC II-rich regions that interconnect the supercomplex within the membrane.

Photosynthetic Reaction Center Complex Proteins↗
PubMed2000

Functional analysis of the PsbX protein by deletion of the corresponding gene in Synechocystis sp. PCC 6803.

The psbX gene (sml0002) coding for a 4.1 kDa protein in Photosystem II of plants and cyanobacteria was deleted in both wild type and in a Photosystem I-less mutant of the cyanobacterium Synechocystis sp. PCC 6803. Polymerase chain reaction and sequencing analysis showed that the mutants had completely segregated. Deletion of the PsbX protein does not seem to influence growth rate, electron transport or water oxidation ability. Whereas a high light induction of the psbX mRNA could be observed in wild type, deletion of the gene did not lead to high light sensibility. Light saturation measurements and 77K fluorescence measurements indicated a minor disconnection of the antenna in the deletion mutant. Furthermore, fluorescence induction measurements as well as immuno-staining of the D1 protein showed that the amount of Photosystem II complexes in the mutants was reduced by 30%. Therefore, PsbX does not seem to be necessary for the Photosystem II electron transport, but directly or indirectly involved in the regulation of the amount of functionally active Photosystem II centres in Synechocystis sp. PCC 6803.

Algal Proteins↗
PubMed2000

Photoactive protochlorophyllide regeneration in cotyledons and leaves from higher plants.

Chlorophyll accumulation during greening implies the continuous transformation of photoactive protochlorophyllide (Pchlide) to chlorophyllide. Since this reaction is a light-dependent step, the study of regeneration of photoactive Pchlide under a continuous illumination is difficult. Therefore this process is best studied on etiolated plants during a period of darkness following the initial photoreduction of photoactive Pchlide. In this study, the regeneration process has been studied using spinach cotyledons, as well as barley and bean leaves, illuminated by a single saturating flash. The regeneration was characterized using 77 K fluorescence emission and excitation spectra and high-performance liquid chromatography. The fluorescence data indicated that the same spectral forms of photoactive Pchlide are regenerated by different pathways: (1) photoactive Pchlide regeneration starts immediately after the photoreduction through the formation of a nonphotoactive Pchlide form, emitting fluorescence at approximately 651 nm. This form is similar to the large aggregate of photoactive Pchlide present before the illumination, but it contains oxidized form of nicotinamide adenine dinucleotide phosphate, instead of the reduced form (NADPH), in the ternary complexes; and (2) after the dislocation of the large aggregates of chlorophyllide-light-dependent NADPH:Pchlide a photooxidoreductase-NADPH ternary complexes, the regeneration occurs at the expense of the several nonphotoactive Pchlide spectral forms present before the illumination.

Cotyledon↗
PubMed2000

Greening of intermittent-light-grown bean plants in continuous light: thylakoid components in relation to photosynthetic performance and capacity for photoprotection.

Phaseolus vulgaris (cvv. Windsor longpod and snap bean) plants, etiolated during germination, were exposed to intermittent light (2 min light every 2 hr) for up to 68 hr and then transferred to continuous white light. On transfer of the plants to continuous light (100 photons mumol m-2 s-1, 24 degrees C), the quantum yield of oxygen evolution increased two-fold in about 30 hr. The chlorophyll content per unit leaf area or unit fresh weight increased dramatically, but the fresh weight per unit leaf area was relatively constant. The changes were expressed on the basis of fresh weight or leaf area. On this basis, the contents of photosystem (PS) I and II increased in continuous light, by a factor of 3 and 8, respectively. While the chlorophyll b content and the contents of apoproteins of light-harvesting chlorophyll-protein complexes (LHCIIb, CP29, CP26 and CP24) increased markedly, neither the total carotenoid content nor the de-epoxidation state of the xanthophylls [ratio of zeaxanthin(Z) + antheraxanthin(A) to (Z + A + violaxanthin) was about 0.4)] responded significantly on transfer to continuous light. The fast rise of the flash-induced electrochromic signal (delta A518) was well correlated with the increases in PS I and PS II reaction centres, and with chlorophyll b and total carotenoid contents. The increase in the quantum yield of oxygen evolution during greening in continuous light is attributed to a more balanced distribution of excitation energy between the two photosystems, facilitated by the increased number of PS II units, the increased antenna size of each unit and the enhancement of grana formation. The chloroplast in intermittent light was found to contain abundant xanthophyll cycle pigments and the psbS gene product, presumably adequate for photoprotection in continuous light as soon as chlorophyll a/b- protein complexes are synthesized. The results suggest that greening in continuous light is accompanied by adjustments that include enhanced quantum efficiency of photosynthesis and development of a capacity for harmless dissipation of excess excitation energy.

Fabaceae↗
PubMed1999

A cyanobacterial gene family coding for single-helix proteins resembling part of the light-harvesting proteins from higher plants.

In the cyanobacterium Synechocystis sp. PCC 6803 five genes were identified with significant sequence similarity to regions of members of the eukaryotic chlorophyll a/b binding gene family (Cab family) and to hliA, a gene coding for a small high-light-induced protein in Synechococcus sp. PCC 7942. Four of these five genes are 174-213 bp in length and code for small proteins predicted to have a single transmembrane helix. The fifth Cab-like gene in Synechocystis sp. PCC 6803 is much longer and codes for a protein of which the N-terminal 80% resemble ferrochelatase but the C-terminal domain has similarity to Cab regions. The small genes were expressed preferentially in the absence of photosystem I, but gene expression was not significantly enhanced at moderately high light intensity. Therefore they were not designated as hli (high-light-induced) as was done for the Synechococcus sp. PCC 7942 homolog. Instead, the genes have been named scp, as the corresponding polypeptides of Synechocystis sp. PCC 6803 are small Cab-like proteins (SCP). The scpA gene, which codes for ferrochelatase with a C-terminal Cab-like extension, was interrupted by the insertion of a kanamycin-resistance cassette between the ferrochelatase and Cab-like gene domains. In the PS I-less background, interruption of scpA was found to lead to increased tolerance to high light intensity and to the requirement of a slightly higher light intensity to drive photosystem II electron transfer, suggestive of decreased light-harvesting efficiency in the absence of the C-terminal extension of ScpA. Immunodetection of ScpC and ScpD indicated that either or both accumulated in PS I-less strains. These proteins were also detected in bands of more than 45 kDa on denaturing gels, raising the possibility that they may occur as stable oligomers. The SCPs represent a new group of cyanobacterial proteins that, in view of their primary structure and response to deletion of photosystem I, are likely to be involved in transient pigment binding.

Amino Acid Sequence↗
PubMed1998

Engineering of N-terminal threonines in the D1 protein impairs photosystem II energy transfer in Synechocystis 6803.

Mutants of the cyanobacterium Synechocystis sp. PCC 6803 with N-terminal changes in the photosystem (PSII) II D1 protein were analysed by flash-induced oxygen evolution, chlorophyll a fluorescence decay kinetics and 77 K fluorescence emission spectra. The data presented here show that mutations of the Thr-2, Thr-3 and Thr-4 in D1 do not influence the oxygen evolution. A perturbation on the acceptor side was observed and the importance of the N-terminal threonines for an efficient energy transfer between the phycobilisome and PSII and for stability of the PSII complex was demonstrated.

Amino Acid Substitution↗
PubMed1998

[Functional MRT of the LS in an open magnet system--the initial results].

PURPOSE: Description of the procedure and first results with functional MRI of the lumbar spine for the investigation of discoligamentous instability. MATERIAL AND METHOD: 21 patients--11 female and 10 male--were studied with rapid True-FISP- and FLASH sequences. With the intention to document movements in maximal ante- and retroflexion a special kidney belt was used containing an inserted multi-purpose flexible coil. With this approach reproducible functional studies can be obtained. RESULTS: Movements in ante- and retroflexion could be performed manually and gradually without technical limitation of restrictions due to the equipment. The location of a patient's pain was determined by indication from the patient and correlated with the finding on the functional MR images. In 71% of patients a gain of information was obtained with regard to discoligamentous instability of the lumbar spine when compared to earlier studies (CT, MRI in neutral position). CONCLUSIONS: Functional MRI of the lumbar spine can contribute additional segmental information and contribute to further therapy planning. With this method discoligamentous instability can be documented, which is less likely with static MRI in a closed MR system.

Adolescent↗
PubMed1996

Developmental regulation of the PsbS gene expression in spinach seedlings: the role of phytochrome.

The PsbS gene product (PSII-S) which is an integral subunit of photosystem II has recently been reported to be a new type of pigment-binding protein [11]. The chlorophylls of the PSII-S protein exhibit weak excitonic coupling and this protein is stable also in the absence of pigments. Here we investigated the expression of the PsbS gene in etiolated spinach seedlings grown either in complete darkness or exposed to light of various qualities. The results obtained reveal that the PsbS gene expression in etiolated spinach plants is subjected to endogenous control. This developmental control occurs at different levels of gene expression and results in transient accumulation of the PsbS transcripts with progressing etiolation. During the first two days after emerging of the cotyledons from the seed coat the steady-state level of the PsbS transcripts is regulated mainly through increased transcriptional activity of the PsbS gene. Prolonged growth of the seedlings in the dark resulted in additional post-transcriptional control of the PsbS transcript level. Translational activity of PsbS mRNA estimated by an integration of mRNA into polysomal complexes shows that the translation rate of PsbS mRNA is less influenced by seedling age. The maximal rate of translation is reached at the first day after cotyledons emergence but the translational activity of PsbS mRNA remains still high (50% of maximum) in 8-day old etiolated spinach plants. In addition to the light-independent developmental control, the PsbS gene expression is positively regulated by phytochrome in etiolated seedlings exposed to light. Red light, however, negatively influences the abundance of PsbS transcripts at post-transcriptional level. Studies on blue or far-red light effects reveal that the accumulation of PsbS transcripts exhibits the characteristics of very-low-fluence responses of the phytochrome receptor.

Cell Nucleus↗
PubMed1996

Metabolic profiles of minimally absorbed orlistat in obese/overweight volunteers.

To determine the metabolic profile of minimally absorbed orlistat in obese/overweight patients, an open-label, single-dose study was performed in eight obese/overweight volunteers between 23 and 68 years of age. Each subject received a single oral dose of 360 mg orlistat containing approximately 400 muCi of 14C-labeled orlistat. Serial blood samples were collected at specified times over 10 hours after administration of orlistat for determination of total radioactivity, unchanged orlistat, and major metabolites in the plasma. Urine samples were collected over 24 hours and analyzed to evaluate the urinary recovery of total radioactivity and the profile of orlistat metabolites in the urine. In addition, all fecal samples were collected and analyzed for total radioactivity. Urinary and fecal recovery of the administered dose of total radioactivity were 1.13 +/- 0.50% (24-hour data only) and 96.4 +/- 18.1% (n = 7), respectively. Maximum observed concentration (Cmax) and time to Cmax (tmax) values of plasma total radioactivity were 150 +/- 51 ng.eq/mL and 6.8 +/- 1.5 hrs, respectively. All these parameters obtained in obese/ overweight subjects were similar to those reported previously in healthy subjects. On the basis of the area under the concentration-time curve from 0 to 10 hours (AUC0-10), two major metabolites comprise a total of approximately 42% of the total radioactivity in plasma. The primary metabolite (M1) has a short half-life (approximately 2 hours), whereas the secondary metabolite (M3) disappeared at a slower rate. No strikingly apparent difference in the urinary metabolic profile was observed between two gender groups. It is concluded that the disposition of orlistat appears to be similar between normal and obese/overweight subjects. Of the minimal fraction of the dose that was absorbed systemically, the presence of two major metabolites accounts for approximately 42%.

Absorption↗
PubMed1995

The nuclear-encoded chlorophyll-binding photosystem II-S protein is stable in the absence of pigments.

The 22-kDa chlorophyll a/b-binding protein (CAB) (psbS gene product) is associated with photosystem II and related to the CAB gene family. Here we report that the PSII-S protein unlike other chlorophyll-binding proteins is stable in the absence of pigments. It is present in etiolated spinach plants and accumulates in the dark progressively with the cellular development of the seedlings. Furthermore, it is present in several pigment-deficient mutants. Analysis of the pigment composition of the PSII-S protein isolated from etiolated plants suggests that neither carotenoids nor chlorophyll precursors are involved in its stabilization in the dark. Exposure of etiolated spinach to light leads to further accumulation of the PSII-S protein, which appears more early than other chlorophyll-binding proteins. Accumulation of the PSII-S protein in green plants is developmentally regulated and restricted to photosynthetic tissues. It is suggested that the function of the PSII-S protein may not be light-harvesting but it could act as a ligand chaperone required for transient binding of pigments during biogenesis or turnover of chlorophyll-binding proteins. Such function would be essential for coordination between pigment biosynthesis and ligation as well as avoiding toxic effects of non-bound chlorophyll molecules.

Carotenoids↗
PubMed1995

The PSII-S protein of higher plants: a new type of pigment-binding protein.

An intrinsic 22 kDa protein of photosystem II has been shown to possess high sequence homology with the CAB gene products, but differs from these proteins by an additional putative fourth transmembrane helix. This protein, designated PSII-S in accordance with the assignment of the name psbS to its gene, has been isolated by nonionic detergents and preparative isoelectric focusing in this study. The isolated PSII-S protein was shown to bind 5 chlorophyll molecules (a and b) per protein unit and also several different kinds of carotenoids. The room temperature absorption spectrum of the Qy transition of the chlorophylls bound to the isolated protein is characterized by a broad band with a maximum at 671 nm. The 77 K fluorescence spectrum exhibits a peak at 672 nm. A single photon counting technique was applied to resolve the room temperature decay kinetics of the first excited singlet states in the chlorophyll ensemble of the PSII-S protein. The data can be satisfactorily described by triexponential kinetics with lifetimes of tau 1 = 1.8 ns, tau 2 = 4.4 ns, and tau 3 = 6.1 ns and normalized amplitudes of 0.09, 0.60, and 0.31, respectively. Circular dichroism spectra suggest that, in contrast to LHCII, virtually no pigment coupling exists in the PSII-S protein. Two copies of the PSII-S protein were found per PSII in spinach thylakoids. It displays an unusually extreme lateral heterogeneity, since the PSII beta centers located in the stroma exposed thylakoid regions contained only residual amounts of the PSII-S protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Carrier Proteins↗
PubMed1995

A nuclear-encoded subunit of the photosystem II reaction center.

A nuclear-encoded polypeptide of 6.1 kDa was identified in isolated photosystem II (PSII) reaction center from Spinacia oleracea. The hydrophobic membrane protein easily escapes staining procedures such as Coomassie R-250 or silver staining, but it is clearly detected by immunodecoration with peptide-directed IgG. This additional subunit was found to be present in PSII reaction centers previously known to contain only the D1/D2/cytb559 proteins and the psbI gene product. Furthermore, cross-linking experiments using 1-(3-dimethylaminopropyl-) 3-ethylcarbodiimide showed that the nearest neighbors were the D1 and D2 proteins and the cytb559. The 6.1-kDa protein was purified by immune affinity chromatography. N-terminal sequence analysis of the isolated protein confirmed the identity of the 6.1-kDa protein and enabled finding of strong similarities with a randomly obtained cDNA from Arabidopsis thaliana. Using enzyme-linked immunosorbent assay in combination with thylakoid membrane preparations of different orientation, the N terminus of the protein, predicted to span the membrane once, is suggested to be exposed at the lumen side of the membrane. Consequently the 6.1-kDa protein seems to be the only subunit in the PSII reaction center that is nuclear encoded and has its N terminus on the lumen side of the membrane. These findings open for new interesting suggestions concerning the properties of photosystem II reaction center with respect to the photosynthetic activity, regulation and assembly in higher plants.

Amino Acid Sequence↗