The work describes a novel approach for sustained photobiological production of H 2 gas via the reversible hydrogenase pathway in the green alga Chlamydomonas reinhardtii. This single-organism, two-stage H 2 production method circumvents the severe O 2 sensitivity of the reversible hydrogenase by temporally separating photosynthetic O 2 evolution and carbon accumulation (stage 1) from the consumption of cellular metabolites and concomitant H 2 production (stage 2). A transition from stage 1 to stage 2 was effected upon S deprivation of the culture, which reversibly inactivated photosystem II (PSII) and O 2 evolution. Under these conditions, oxidative respiration by the cells in the light depleted O 2 and caused anaerobiosis in the culture, which was necessary and sufficient for the induction of the reversible hydrogenase. Subsequently, sustained cellular H 2 gas production was observed in the light but not in the dark. The mechanism of H 2 production entailed protein consumption and electron transport from endogenous substrate to the cytochrome b 6 -f and PSI complexes in the chloroplast thylakoids. Light absorption by PSI was required for H 2 evolution, suggesting that photoreduction of ferredoxin is followed by electron donation to the reversible hydrogenase. The latter catalyzes the reduction of protons to molecular H 2 in the chloroplast stroma.

We have isolated and characterized a second [Fe]-hydrogenase gene from the green alga, Chlamydomonas reinhardtii. The HydA2 gene encodes a protein of 505 amino acids that is 74% similar and 68% identical to the known HydA1 hydrogenase from C. reinhardtii. HydA2 contains all the conserved residues and motifs found in the catalytic core of the family of [Fe]-hydrogenases. We demonstrate that both the HydA1 and the HydA2 transcripts are expressed upon anaerobic induction, achieved either by neutral gas purging or by sulfur deprivation of the cultures. Furthermore, the expression levels of both transcripts are regulated (in some cases differently) by incubation conditions, such as the length of anaerobiosis, the readdition of O 2 , the presence of acetate, and/or the absence of nutrients such as sulfate during growth. Antibodies specific for HydA2 recognized a protein of about 49 kDa in extracts from anaerobically induced C. reinhardtii cells, strongly suggesting that HydA2 encodes for an expressed protein. Homology-based 3D modeling of the HydA2 hydrogenase shows that its catalytic site models well to the known structure of Clostridium pasteurianum CpI, including the H 2 -gas channel. The major differences between HydA1, HydA2 and CpI are the absence of the N-terminal Fe-S centers and the existence of extra sequences in the algal enzymes. To our knowledge, this work represents the first systematic study of expression of two algal [Fe]hydrogenases in the same organism.

This study investigated the immature platelet fraction (IPF) in assessing treatment effects in immune thrombocytopenia (ITP). IPF was measured on the Sysmex XE2100 autoanalyzer. The mean absolute-IPF (A-IPF) was lower for ITP patients than for healthy controls (3.2 vs 7.8 ؋ 10 9 /L, P < .01), whereas IPF percentage was greater (29.2% vs 3.2%, P < .01).

Objective-Plant-derived ␣-linolenic acid (ALA) may constitute an attractive cardioprotective alternative to fish-derived n-3 fatty acids. However, the effect of dietary ALA on arterial thrombus formation remains unknown. Methods and Results-Male C57Bl/6 mice were fed a high-ALA or low-ALA diet for 2 weeks. Arterial thrombus formation was delayed in mice fed a high-ALA diet compared with those on a low-ALA diet (nϭ7; PϽ0.005). Dietary ALA impaired platelet aggregation to collagen and thrombin (nϭ5; PϽ0.005) and decreased p38 mitogen-activated protein kinase activation in platelets. Dietary ALA impaired arterial tissue factor (TF) expression, TF activity, and nuclear factor-B activity (nϭ7; PϽ0.05); plasma clotting times and plasma thrombin generation did not differ (nϭ5; Pϭnot significant). In cultured human vascular smooth muscle and endothelial cells, ALA inhibited TF expression and activity (nϭ4; PϽ0.01). Inhibition of TF expression occurred at the transcriptional level via the mitogen-activated protein kinase p38 in smooth muscle cells and p38, extracellular signal-regulated kinases 1 and 2, and c-Jun N-terminal kinases 1 and 2 in endothelial cells. Conclusion

Ca 2؉ signals mediate the hepatic effects of numerous hormones and growth factors. Hepatic Ca 2؉ signals are elicited by the inositol trisphosphate receptor, an intracellular Ca 2؉ channel. Three isoforms of this receptor have been identified; they are expressed and regulated differently. We investigated the effect of liver fibrosis and cirrhosis on the hepatic expression of the inositol trisphosphate receptor isoforms. Two different rat models were used: bile duct ligation (fibrosis) and chronic exposure to CCl 4 /phenobarbital (cirrhosis). Messenger RNA levels were determined by ribonuclease protection assay (RPA), competitive polymerase chain reaction (PCR) followed by Southern blotting, and real-time quantitative PCR. Protein expression was assessed by Western blotting; tissue distribution was assessed by immunohistology. In control animals, isoform 2 was the predominant isoform, isoform 1 represented less than one third, and isoform 3 less than 1%. After bile duct ligation, expression of types 1 and 3 increased 1.9-and 5.7-fold, and expression of type 2 decreased 2.5-fold at the protein level. After exposure to CCl 4 /phenobarbital, expression of types 1, 2, and 3 were 2.4-, 0.9-, and 4.2-fold their expression in control animals. Type 2 was localized to the apical domain of hepatocytes, consistent with a role for Ca 2؉ signals in canalicular function. Type 3 was detectable in intrahepatic bile duct epithelial cells and not in hepatocytes, suggesting that Ca 2؉ signals may be regulated differently in these cells. Signaling through inositol trisphosphate receptor participates in the pathogenesis of cirrhosis, because this process affects the expression of its isoforms. (HEPATOLOGY 1999;30:1018-1026.)Development of cirrhosis implies not only remodeling of the liver architecture, but also dramatic changes in the functions of hepatic cells. These changes are orchestrated by a network of receptors, protein-kinases, and transducers that compose complex signaling pathways. Among them, the inositol 1,4,5-trisphosphate receptor (IP 3 R) plays a central role. 1 Numerous hormones and growth factors bind to receptors on plasma membrane to stimulate the production of inositol 1,4,5-trisphosphate (IP 3 ) and to trigger IP 3 -dependent Ca 2ϩ release through the Ca 2ϩ channel of the IP 3 R. 2 Ca 2ϩ signals regulate many cellular functions from gene expression and cellular division to metabolic pathways and cellular secretion. 1 Both hepatocytes and biliary epithelial cells demonstrate complex Ca 2ϩ signals, which rely essentially on IP 3 R, because the ryanodine receptor, another intracellular Ca 2ϩ channel, could not be detected in liver. 3 In response to hormonal stimulation, intracellular Ca 2ϩ concentration oscillates in hepatocytes and even forms Ca 2ϩ waves through the entire lobule. 4 Hepatocellular Ca 2ϩ signals start in a specific apical location and diffuse in an apical to basal manner. 5 IP 3 -dependent Ca 2ϩ signals stimulate bile canalicular contractions, an effect blocked by nitric oxide. 6 In intrahepatic bil...

SummaryWe studied the inhibition of platelet microparticle (MP) formation and thrombin generation under high shear forces. We hypothesized that an inhibitor of the GPIbα-von Willebrand factor (vWF) interaction would be more effective in suppressing MP formation and thrombin generation than GPIIb/IIIa inhibitors. Platelet-rich plasma (PRP) anticoagulated with PPACK (D-Phe-Pro-Arg chloromethyl ketone) was exposed in a coneand-plate viscometer (shear: 5,000 s−1 for5 min) in the presence of antagonists to GPIbα (the monoclonal antibody [Mab] Ib-23) or to GPIIb/IIIa (abciximab, tirofiban, eptifibatide) at their IC90 determined in platelet aggregometry with ristocetin or ADP, respectively. We used double labeling (CD41-PE and annexin-V-FITC) for flow cytometric detection of MP and their aminophospholipid exposure. Thrombin generation was measured using PRP prepared fromACD anticoagulated blood. About 40% of the thrombin generation was found to be mediated by the MP fraction of the PRP. Blockade of GPIbα with Mab Ib-23 reduced MP formation and thrombin generation by 50%, and was more effective than any GPIIb/IIIa antagonist. The combination of Mab Ib-23 with one of the GPIIb/IIIa inhibitors further reduced the MP formation to ∼30%. The antibody also partially inhibited thrombin induced platelet aggregation. Epitope mapping suggested that Mab Ib-23 binds between the amino acids 201 and 268 of GPIbα, explaining the interference with vWF and thrombin interaction. In contrast to the commonly used GPIIb/IIIa antagonists, the blockade of GPIbα with Mab Ib-23 effectively reduces the prothrombotic MP generation and thrombin formation at shear rates typically found in arterial stenoses.

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It has been known for over half a century that homocysteine levels are elevated in liver cirrhosis, but the basis for it is not fully understood. Using differential display, we identified betaine homocysteine methyltransferase (BHMT) as a gene down-regulated in rat liver cirrhosis and most likely involved in this dysregulation. A partial BHMT clone was isolated by screening of a cDNA library with the differential display fragment. The full-length gene was generated by primer extension of cDNA. Expression levels of BHMT in cirrhotic livers of bile duct ligated rats were compared to controls by Northern and Western blotting as well as by enzyme activity measurements. BHMT mRNA levels were reduced to 29+/-23% in established liver cirrhosis induced by bile duct ligation (BDL) as compared to controls. Enzyme assays in crude liver homogenates showed a similar reduction in BHMT activity in bile duct ligated rat livers. By Western blotting, BHMT could be detected in crude liver homogenates of control animals, but was reduced to below the limit of detection in cirrhotic livers. In conclusion, these findings establish a reduced BHMT enzyme activity in cirrhotic rat livers, which may explain the elevated plasma homocysteine levels in cirrhosis.