Microalgae: a green source of renewable H(2)

This article summarizes recent advances in the field of algal hydrogen production. Two fundamental approaches are being developed. One involves the temporal separation of the usually incompatible reactions of O(2) and H(2) production in green algae, and the second involves the use of classical genetics to increase the O(2) tolerance of the reversible hydrogenase enzyme. The economic and environmental impact of a renewable source of H(2) are also discussed.

Photosynthetic apparatus organization and function in the wild type and a chlorophyll b-less mutant of Chlamydomonas reinhardtii. Dependence on carbon source

The assembly, organization and function of the photosynthetic apparatus was investigated in the wild type and a chlorophyll (Chl) b-less mutant of the unicellular green alga Chlamydomonas reinhardtii, generated via DNA insertional mutagenesis. Comparative analyses were undertaken with cells grown photoheterotrophically (acetate), photomixotrophically (acetate and HCO3-) or photoautotrophically (HCO3-). It is shown that lack of Chl b diminished the photosystem-II (PSII) functional Chl antenna size from 320 Chl (a and b) to about 95 Chl a molecules. However, the functional Chl antenna size of PSI remained fairly constant at about 290 Chl molecules, independent of the presence of Chl b. Western blot and kinetic analyses suggested the presence of inner subunits of the Chl a-b light-harvesting complex of PSII (LHCII) and the entire complement of the Chl a-b light-harvesting complex of PSI (LHCI) in the mutant. It is concluded that Chl a can replace Chl b in the inner subunits of the LHCII and in the entire complement of the LHCI. Growth of cells on acetate as the sole carbon source imposes limitations in the photon-use efficiency and capacity of photosynthesis. These are manifested as a lower quantum yield and lower light-saturated rate of photosynthesis, and as lower variable to maximal (Fv/Fmax) chlorophyll fluorescence yield ratios. This adverse effect probably originates because acetate shifts the oxidation-reduction state of the plastoquinone pool, and also because it causes a decrease in the amount and/or activity of Rubisco in the chloroplast. Such limitations are fully alleviated upon inclusion of an inorganic carbon source (e.g. bicarbonate) in the cell growth medium. Further, the work provides evidence to show that transformation of green algae can be used as a tool by which to generate mutants exhibiting a permanently truncated Chl antenna size and a higher (per Chl) photosynthetic productivity of the cells.

Insulin-like growth factor inhibits vascular contraction to 5-hydroxytryptamine: involvement of tyrosine phosphatase

This study tests the hypothesis that insulin-like growth factor 1 (IGF-1)-induced vasodilation is due to the stimulation of tyrosine phosphatase. Rat aortic segments (endothelium intact) were placed in muscle baths for force measurement. Segments were contracted to serotonin [5-hydroxytyptamine (5-HT), 10(-7)-10(-5) M] before and after incubation with IGF-1 (10-100 nM; 90 min). IGF-1 caused a 20% inhibition of 5-HT-induced contractions. This inhibition was reversed by the tyrosine phosphatase inhibitors sodium orthovanadate and molybdate. Orthovanadate did not alter inhibitory properties of the calcium channel antagonist verapamil, suggesting that the phosphatase inhibitors were relatively specific. IGF-1-induced inhibition was not altered by blockade of nitric oxide synthase. Western blot analysis confirmed that the 5-HT-induced stimulation of tyrosine phosphorylation of the 42-kDa extracellular signal-regulated mitogen-activated protein kinase protein was reduced by IGF-1 (52% inhibition), an inhibition that was attenuated by orthovanadate. These data are consistent with the hypothesis that the vasodilator activity of IGF-1 is mediated by the activation of a tyrosine phosphatase.

Sustained photobiological hydrogen gas production upon reversible inactivation of oxygen evolution in the green alga Chlamydomonas reinhardtii

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.

Transforming growth factor beta, fibrogenesis and hyperglycemia in patients with chronic pancreatitis

It has been suggested that transforming growth factor beta (TGFb) mediates liver fibrosis, which can be monitored by the serum determination of the N-terminal peptide of type III procollagen (PIIIP) and laminin. Fibrosis is also an important phenomenon in patients with chronic pancreatitis (CP). In 23 patients with CP, 38 with liver cirrhosis (LC) and 20 healthy controls we compared the serum patterns of PIIIP, laminin and TGFb and assessed whether in CP these markers are correlated with exocrine and endocrine function. In patients with LC, PIIIP and laminin levels were significantly higher, whereas TGFb levels were significantly lower than those of controls. In CP patients, no significant variations were found for PIIIP and laminin, although levels were high in 7/23 and in 5/23 patients, respectively. TGFb levels in CP patients were higher than those in LC patients, levels being raised in 6/23 patients. In LC patients an inverse correlation was found between PIIIP and TGFb, whereas in CP patients, a direct correlation was found between TGFb and PIIIP. Moreover, in CP patients, there was also a positive correlation between TGFb and fasting serum glucose levels, while laminin was correlated with PABA test results.

IN CONCLUSION

serum biochemical markers of liver fibrosis can be considered of limited value in assessing pancreatic fibrosis; in liver cirrhosis there may be a negative feed-back regulation between TGFb production and the fibrogenetic process; and in chronic pancreatitis TGFb appears to favor fibrosis on the one hand and the development of hyperglycemia on the other.

Primary sclerosing cholangitis (PSC): clinical, laboratory and survival analysis in children and adults

BACKGROUND

Primary sclerosing cholangitis (PSC) is an uncommon disorder, rarely diagnosed in children, moreover, data on its natural history and survival are still lacking.

AIM

The study was undertaken to compare clinical, laboratory and survival rates in two series of PSC: one in a pediatric group (group A) and the other in an adult population (group B).

METHODS

Group A included 9 patients (5 males, 4 females, mean age 10 yrs, range 7-15); group B included 28 patients (19 males, 9 females, mean age 32 years, range 19-60). The mean follow-up was 5.2 years in group A and 6.9 years in group B (range 1-14 years). ERCP and colonoscopy were performed in each case. Survival was analyzed using the Kaplan-Meier method.

RESULTS

At presentation children showed significantly higher levels of IgG and AST compared to adults (p<0.05); moreover, interface hepatitis occurred in 50% of children and in 14.2% in adults (p=ns). During follow-up the following major events occurred: oesophageal bleeding (n=2) in group A; progressive liver failure (n=6), cholangiocarcinoma (n=3), colonic cancer (n=1) in group B. Liver transplantation (OLTx) was performed in 4 adults (one died after a retransplantation). No deaths were observed in children. The Kaplan-Meier curve in adults shows a 65% rate of survival at 10 years.

CONCLUSIONS

The present findings on PSC suggest a more severe activity of the disease in children than in adults at presentation; nonetheless, the prognosis seems to be better in children than in adults. The Mayo score prognostic index does not predict the development of liver/colonic cancer. A poor outcome (defined as death or being listed for OLTx) only occurred in adults.

Oxygen-derived free radical production by peripheral blood neutrophils in chronic cholestatic liver diseases

BACKGROUND/AIMS

Patients with chronic cholestasis, particularly those with associated cirrhosis, are susceptible to infectious complications. From animal models it has been postulated that cholestasis affects systemic polymorphonuclear leukocyte (PMNL) function by impeding chemotaxis, phagocytosis and superoxide release, which are necessary for an adequate immune response. The aim of this study was to evaluate neutrophil activity in the production of oxygen-derived free radicals in chronic cholestatic liver diseases.

METHODOLOGY

The following groups were included in the study: 27 primary biliary cirrhosis (PBC) patients, 12 primary sclerosing cholangitis (PSC) patients, and 3 control groups (29 healthy subjects, 19 patients with HCV-related cirrhosis and 23 ulcerative colitis (UC) patients). Peripheral neutrophils were isolated from heparinized blood samples and PMNL activity was measured by free radical production, using a chemiluminometer, after stimulation with fMLP, PMA and Zymosan. The effect of liver disease severity and degree of cholestasis on PMNL function was also evaluated.

RESULTS

Both PBC and PSC patients exhibited a normal PMNL activity compared to healthy subjects after the three stimuli used. In PBC patients only (but not in PSC patients), the histological stage of the disease seems to positively influence ROS production. Stage IV PBC patients showed a significantly higher PMNL activity compared to HCV-related cirrhotic patients. PSC patients failed to show any difference according to the association with UC.

CONCLUSIONS

The increased susceptibility to bacterial infections in patients with chronic cholestatic liver disease is not related to an impaired PMNL activity. However, our findings may support the influence of biohumoral factors (cytokines?) on PMNL activation.

Photosystem-II damage and repair cycle in chloroplasts: what modulates the rate of photodamage ?

Organisms that rely on oxygenic photosynthesis are subject to the effects of photo-oxidative damage, which impairs the function of photosystem-II (PSII). This phenomenon has the potential to lower rates of photosynthesis and diminish plant growth. Experimental evidence shows that the steady-state oxidation-reduction level of the primary quinone acceptor (QA) of PSII is the parameter that controls photodamage under a variety of physiological and environmental conditions. When QA is reduced, excitation energy at PSII is dissipated via a charge-recombination reaction. Such non-assimilatory dissipation of excitation generates singlet oxygen that might act to covalently modify the photochemical reaction center chlorophyll. Under steady-state photosynthesis conditions, the reduction state of QA increases linearly with irradiance, thereby causing a correspondingly linear increase in the probability of photodamage. It is concluded that there is a low probability that photodamage will occur when QA is oxidized and excitation energy is utilized in electron transport, and a significantly higher probability when QA is reduced in the course of steady-state photosynthesis.

Tumour necrosis factor alpha and cellular proliferation in primary biliary cirrhosis

AIMS

1) To evaluate serum levels and tissue expression of Tumour necrosis factor alpha in primary biliary cirrhosis: 2) to correlate serum tumour necrosis factor alpha levels and cellular proliferation with the severity and prognosis of liver disease.

METHODS

Twenty-nine primary biliary cirrhosis patients (6 stage I, 8 II, 8 III, and 7 IV) entered the study. Serum tumour necrosis factor alpha was measured by EIA (Innogenetics, Antwerp, Belgium). Tissue tumour necrosis factor alpha and Ki-67 were tested by indirect immunoperoxidase staining on liver sections.

RESULTS

Serum tumour necrosis factor alpha increased with the severity of histological stage (from 10.8 +/- 11 pg/ml in stage II to 17.1 +/- 10 in stage III and 22.8 +/- 8.7 in stage IV, p < 0.036). A positive correlation was also found between tumour necrosis factor alpha serum levels and the Mayo score (p < 0.05). A weak and sporadic expression of tumour necrosis factor alpha was observed in the inflammatory infiltrate around the bile ducts. Tissue Ki-67 (expressed as the labelling index in the hepatocellular nuclei) was evaluated in all stages of the disease (1.09 +/- 0.6% in stage I, 1.14 +/- 0.6% in stage II, 2.11 +/- 1.9% in stage III, and 2.67 +/- 2.8% in stage IV; the labelling index was significantly lower in early stages (I/II) than in late stages (III/IV), p < 0.05. A strong correlation between Ki-67 and the Mayo score was observed (p < 0.0005).

CONCLUSIONS

1) tumour necrosis factor alpha production seems related to the severity and the prognosis of primary biliary cirrhosis; 2) liver mononuclear cells in the inflammatory infiltrate do not seem to be the major site of tumour necrosis factor alpha release; 3) cellular proliferation is correlated with the severity of liver disease.

Separation of oligonucleotides and DNA fragments by capillary electrophoresis in dynamically and permanently coated capillaries, using a copolymer of acrylamide and beta-D-glucopyranoside as a new low viscosity matrix with high sieving capacity

New copolymers of acrylamide and beta-D-glucopyranoside were synthesized and characterized. The different reactivity of the two monomers towards radical polymerization meant we could control the growth of the polymer chains whose length was inversely related to the number of glucose residues incorporated in the copolymers. The properties of these polymers were investigated in the separation of oligonucleotides and double-stranded DNA by capillary electrophoresis (CE) in coated and uncoated capillaries. The new copolymers were a suitable matrix for CE due to their high-resolving capacity and low viscosity. We also looked into the advantages of a new method of dynamic suppression of electroosmotic flow based on the addition of small amounts (0.03-0.05%) of dimethylacrylamide to the sieving and to the running buffer. A complete test was run on the reproducibility and efficiency of separations carried out in a permanently and dynamically coated capillary, and the advantages and disadvantages of the two methods were compared.

Photoinhibitory damage is modulated by the rate of photosynthesis and by the photosystem II light-harvesting chlorophyll antenna size

We investigated the effect of photosynthetic electron transport and of the photosystem II (PSII) chlorophyll (Chl) antenna size on the rate of PSII photoinhibitory damage. To modulate the rate of photosynthesis and the light-harvesting capacity in the unicellular chlorophyte Dunaliella salina Teod., we varied the amount of inorganic carbon in the culture medium. Cells were grown under high irradiance either with a limiting supply of inorganic carbon, provided by an initial concentration of 25 mM NaHCO3, or with supplemental CO2 bubbled in the form of 3% CO2 in air. The NaHCO3-grown cells displayed slow rates of photosynthesis and had a small PSII light-harvesting Chl antenna size (60 Chl molecules). The half-time of PSII photodamage was 40 min. When switched to supplemental CO2 conditions, the rate of photodamage was retarded to a t1/2 = 70 min. Conversely, CO2-supplemented cells displayed faster rates of photosynthesis and a larger PSII light-harvesting Chl antenna size (500 Chl molecules). They also showed a rate of photodamage with t1/2 = 40 min. When depleted of CO2, the rate of photodamage was accelerated (t1/2 = 20 min). These results indicate that the in-vivo susceptibility to photodamage is modulated by the rate of forward electron transport through PSII. Moreover, a large Chl antenna size enhances the rate of light absorption and photodamage and, therefore, counters the mitigating effect of forward electron transport. We propose that under steady-state photosynthesis, the rate of light absorption (determined by incident light intensity and PS Chl antenna size) and the rate of forward electron transport (determined by CO2 availability) modulate the oxidation/reduction state of the primary PSII acceptor QA, which in turn defines the low/high probability for photodamage in the PSII reaction center.

The regulation of photosynthetic electron transport during nutrient deprivation in Chlamydomonas reinhardtii

The light-saturated rate of photosynthetic O2 evolution in Chlamydomonas reinhardtii declined by approximately 75% on a per-cell basis after 4 d of P starvation or 1 d of S starvation. Quantitation of the partial reactions of photosynthetic electron transport demonstrated that the light-saturated rate of photosystem (PS) I activity was unaffected by P or S limitation, whereas light-saturated PSII activity was reduced by more than 50%. This decline in PSII activity correlated with a decline in both the maximal quantum efficiency of PSII and the accumulation of the secondary quinone electron acceptor of PSII nonreducing centers (PSII centers capable of performing a charge separation but unable to reduce the plastoquinone pool). In addition to a decline in the light-saturated rate of O2 evolution, there was reduced efficiency of excitation energy transfer to the reaction centers of PSII (because of dissipation of absorbed light energy as heat and because of a transition to state 2). These findings establish a common suite of alterations in photosynthetic electron transport that results in decreased linear electron flow when C. reinhardtii is limited for either P or S. It was interesting that the decline in the maximum quantum efficiency of PSII and the accumulation of the secondary quinone electron acceptor of PSII nonreducing centers were regulated specifically during S-limited growth by the SacI gene product, which was previously shown to be critical for the acclimation of C. reinhardtii to S limitation (J.P. Davies, F.H. Yildiz, and A.R. Grossman [1996] EMBO J 15: 2150-2159).

S-adenosylmethionine versus ursodeoxycholic acid in the treatment of intrahepatic cholestasis of pregnancy: preliminary results of a controlled trial

OBJECTIVES

To evaluate the efficacy of S-adenosylmethionine (SAMe) and ursodeoxycholic acid (UDCA) in intrahepatic cholestasis of pregnancy (ICP).

METHODS

Twenty patients in the last trimester of pregnancy were randomly assigned to receive either SAMe (1000 mg/day i.m.) or UDCA (450 mg/day) until delivery; the treatment lasted at least 15 days in all cases.

RESULTS

After UDCA the women exhibited significantly lower levels of total bile acids (P < 0.02), but no significant differences were noted in AST, ALT, or alkaline phosphatase. All ten patients showed a complete resolution of pruritus. After SAMe no significant changes were noted in pruritus, total bile acids or liver function tests. No adverse reactions on mother or child were recorded during either UDCA or SAMe treatment and the outcome of pregnancy was favorable in both groups.

CONCLUSIONS

These findings show that UDCA is more effective than SAMe in controlling pruritus and total bile acids, which are considered a prognostic parameter in ICP with respect to the fetus. Nevertheless, before UDCA is introduced as an effective and safe treatment for ICP, which also has a beneficial effect on fetal prognosis, we believe these results should be confirmed and extended in other clinical trials.

Chromatic regulation inChlamydomonas reinhardtii alters photosystem stoichiometry and improves the quantum efficiency of photosynthesis

The work addressed the adjustment of the photosystem ratio in the green algaChlamydomonas reinhardtii. It is shown that green algae, much like cyanophytes and higher plants, adjust and optimize the ratio of the two photosystems in chloroplasts in response to the quality of irradiance during growth. Such adjustments are compensation reactions and helpC. reinhardtii to retain a quantum efficiency of oxygen evolution near the theoretical maximum. Results show variable amounts of PS I and a fairly constant amount of PS II in chloroplasts and suggest that photosystem stoichiometry adjustments, occurring in response to the quality of irradiance during plant growth, are mainly an adjustment in the concentration of PS I. The work delineates chromatic effects on chlorophyll accumulation in the chloroplast ofC. reinhardtii from those pertaining to the regulation of the PS I/PS II ratio. The detection of the operation of a molecular feedback mechanism for the PS I/PS II ratio adjustment in green algae strengthens the notion of the highly conserved nature of this mechanism among probably all oxygen evolving photosynthetic organisms. Findings in this work are expected to serve as the basis of future biochemical and mutagenesis experiments for the elucidation of the photosystem ratio adjustment in oxygenic photosynthesis.

Localization and characterization of a novel 20 kDa polypeptide in the chloroplast of the green alga Dunaliella salina

Recent work with the green alga Dunaliella salina showed the presence of a approximately 20 kDa chloroplast protein that was recognized by polyclonal antibodies raised against the isolated LHC-II [Webb M.R. and Melis A. (1995) Plant Physiol. 107: 885]. In this report, a characterization of the approximately 20 kDa polypeptide is presented. It is shown that it is localized in the chloroplast envelope membrane of D. salina. The abundance of this protein is constant on a per cell basis and independent of the light regime during cell growth. The approximately 20 kDa polypeptide is easily degraded to a approximately 19 kDa product during sample preparation. A limited amino acid sequence of 21 residues from the free N-terminus of the approximately 19 kDa product was obtained. On the basis of this partial sequence, it was concluded that the approximately 20 kDa polypeptide is not a degradation product of a known LHC-II but rather a novel protein. The approximately 20 kDa polypeptide did not cross-react with antibodies raised against the Cbr (carotene biosynthesis-related) gene product and showed a different electrophoretic mobility from the latter. Light-shift experiments suggest that the approximately 20 kDa polypeptide is not an ELIP (early light-inducible protein). Possible functions of the approximately 20 kDa protein are discussed.

Characterization of a 160 kD Photosystem II reaction center complex isolated from photoinhibited Dunaliella salina thylakoids

Photoinhibition in the green alga Dunaliella salina is accompanied by the formation of inactive Photosystem II reaction centers. In SDS-PAGE analysis, the latter appear as 160 kD complexes. These complexes are structurally stable, enough to withstand re-electrophoresis of excised gel slices from the 160 kD region. Western blot analyses with specific polyclonal antibodies raised against the D1 or D2 reaction center proteins provided evidence for the presence of both of these polypeptides in the re-electrophoresed 160 kD complex. Incubation of excised gel slices from the 160 kD region, under aerobic conditions at 4°C for a prolonged period of time, caused a break-up of the 160 kD complex into a ∽52 kD D1-containing and ∽80 and ∽26 kD D2-containing pieces. Western blot analysis with polyclonal antibodies raised against the apoproteins of CPI (reaction center proteins of PS I) did not show cross-reaction either with the 160 kD complex or with the ∽52, ∽80 and ∽26 kD pieces. The results show the presence of both D1 and D2 in the 160 kD complex and strengthen the notion of a higher molecular weight D1- and D2-containing complex that forms upon disassembly of photodamaged PS II units.

The role of chloroplast-encoded protein biosynthesis on the rate of D1 protein degradation in Dunaliella salina

Mechanistic aspects of the Photosystem II (PS II) damage and repair cycle in Dunaliella salina were investigated. The work addressed the role of chloroplast-encoded protein biosynthesis on the rate of the D1 protein (chloroplast psbA gene product) degradation, following photoinhibition of PS II under in vivo conditions. Cells were grown under different light-intensities and the rate of D1 photodamage and degradation was measured via pulse-chase measurements with ((35)S)sulfate. It is shown that no detectable difference exists in the rate of D1 degradation in D. salina, measured in the presence or absence of lincomycin, a chloroplast protein biosynthesis inhibitor. The results suggest that de novo D1 biosynthesis does not play a role in the regulation of D1 degradation. In low-light (100 μmol photons m(-2) s(-1)) grown cells, the rate of photodamage to D1 did not exceed the rate of its degradation and replacement. In high-light (2200 μmol photons m(-1) s(-1)) grown cells, the rate of D1 photodamage was faster than the rate of its degradation, resulting in a significant accumulation of photoinactivated PS II centers in the chloroplast thylakoids (chronic photoinhibition). The latter was coincident with the appearance of a 160 kD complex that contained photodamaged D1. Electron micrographs of D. salina thylakoids revealed extensive grana stacks in the thylakoid membrane of low-light grown cells. Only rudimentary appressions consisting of simple membrane pairings were found in the high-light grown cells. The results are discussed in terms of the regulation of D1 degradation in chloroplasts under in vivo conditions.

Isolation of a differentially regulated splicing isoform of human NF-E2

The transcription factor NF-E2 (nuclear factor erythroid 2), interacting via DNA motifs within regulatory regions of several hematopoietic genes, is thought to mediate the enhancer activity of the globin locus control regions. By screening a human fetal liver cDNA library with probes derived from mouse NF-E2, we have isolated a splicing variant of the NF-E2 gene (fNF-E2) that differs in the 5' untranslated region from the previously reported cDNA (aNF-E2). The fNF-E2 isoform is transcribed from an alternative promoter located in the 3' end of the first intron and joined by alternative splicing to the second and third exons, which are shared by both RNA isoforms. Although the two forms produce the same protein, they are expressed in different ratios during development. fNF-E2 is more abundant in the fetal liver and less abundant in the adult bone marrow compared to the previously described form. Their distribution apparently follows the differential expression of fetal and adult hemoglobins.

Chloroplast Response in Dunaliella salina to Irradiance Stress (Effect on Thylakoid Membrane Protein Assembly and Function)

The chloroplast response in the green alga Dunaliella salina to irradiance stress was investigated. Cells were grown under low light (LL) at 100 [mu]mol photons m-2 s-1 or high light (HL) at 2000 [mu]mol photons m-2 s-1 incident intensity. LL-grown cells had a low chlorophyll (Chl) a/b ratio, an abundance of light-harvesting complex II proteins (LHC-II), and a large Chl antenna size. HL-grown cells had a higher Chl a/b ratio, relatively fewer LHC-II, and a small Chl antenna size. The more abundant higher molecular mass subunits of the LHC-II (approximately 31 kD) were selectively depleted from the thylakoid membrane of HL-grown cells. Light-shift experiments defined the kinetics of change in the subunit composition of the LHC-II and suggested distinct mechanisms in the acclimation of thylakoids to HL or LL conditions. The results showed that irradiance exerts a differential regulation on the expression of various Lhcb genes. The specific polyclonal antibodies used in this work, raised against the purified LHC-II, cross-reacted with a polypeptide of approximately 20 kD in HL-grown samples. In this work we examined the dynamics of induction of this novel protein and discuss its function in terms of a chloroplast response to the level of irradiance.

Hyperinsulinemia and hypertension. Do intestinal hormones play a role?

Gastric inhibitory polypeptide (GIP) is one of the strongest insulinotropic gut factors. Its secretion is induced by oral (but not intravenous) glucose and it has been implicated in the pathogenesis of hyperinsulinemic states (NIDDM, obesity). To determine its relevance to hypertension, 54 subjects were studied: 26 normotensives (12 with and 14 without family history of essential hypertension), and 28 essential hypertensive subjects. Plasma glucose, serum insulin (IRI), and GIP were evaluated after a mixed meal containing a total of 82 g of carbohydrates, and 2 g sodium chloride. Venous blood was collected at baseline and every 15 min during a 3-h period. Baseline levels of glucose, IRI, and GIP were comparable in the three groups. At 30 min, however, IRI and GIP were higher in normotensives with a family history of hypertension and in established hypertensive versus control subjects. Both in normotensive and in hypertensive groups, glucose, IRI, and GIP responses to the meal were significantly correlated. Our data suggest the contribution of altered GIP secretion in the pathogenesis of hyperinsulinemia in essential hypertension.

Photosystem II reaction center damage and repair cycle: chloroplast acclimation strategy to irradiance stress

A daily occurrence in the life of a plant is the function of a photosystem II (PSII) damage and repair cycle in chloroplasts. This unique phenomenon involves the frequent turnover of D1, the 32-kDa reaction-center protein of PSII (chloroplast psbA gene product). In the model organism Dunaliella salina (a green alga), growth under low light (100 mol of photons per m2 per sec) entails damage, degradation, and replacement of D1 every 7 hr. Growth under irradiance stress (2200 micromol of photons per m2 per sec) entails damage to D1 every 20 min. The rate of de novo D1 biosynthesis under conditions of both low light and irradiance stress was found to be fairly constant on a per chloroplast or cell basis. The response of D. salina to the enhanced rate of damage entails an accumulation of photodamaged centers (80% of all PSII) and the formation of thylakoid membranes containing a smaller quantity of photosystem I (PSI) centers (about 10% of that in cells grown under low light). These changes contribute to a shift in the PSII/PSI ratio from 1.4:1 under low-light conditions to 15:1 under irradiance stress. The accumulation of photodamaged PSII under irradiance stress reflects a chloroplast inability to match the rate of D1 degradation or turnover with the rate of damage for individual PSII complexes. The altered thylakoid membrane organization ensures that a small fraction of PSII centers remains functional under irradiance stress and sustains electron flow from H2O to ferredoxin with rates sufficient for chloroplast photosynthesis and cell growth.

Markers of hepatitis C virus infection in Sardinian blood donors: relationship with alanine aminotransferase levels

Serum samples from 1,765 consecutive Sardinian blood donors, negative for hepatitis B surface antigen (HBsAg) and for antibodies to human immunodeficiency virus (HIV) (anti-HIV), were evaluated for the presence of antibodies to hepatitis C virus (anti-HCV) by second-generation ELISA. Anti-HCV was detected in 25 (1.45%) of the 1,765 donors examined. Anti-HCV was found in 15 of the 1,690 (0.9%) donors with normal alanine aminotransferase (ALT) and in 10 of the 75 (13%) donors with elevated ALT (P < 0.0001). Of the 15 anti-HCV-positive donors with normal ALT, only five (33%) were confirmed to be positive by second-generation RIBA, six (40%) were indeterminate, while four (27%) were RIBA negative. HCV RNA, as detected by polymerase chain reaction (PCR) using a set of primers from the 5'-noncoding region, was found in six of the 15 (40%) donors with normal ALT, including five RIBA positive and one indeterminant. Of the 10 anti-HCV-positive donors with elevated ALT, all were RIBA positive and eight (80%) had detectable HCV RNA. Thus, among ELISA-reactive donors, those with elevated ALT had a significantly higher probability of being positive for second-generation RIBA and HCV RNA compared to those with normal ALT levels (P = 0.028). None of the 65 donors with elevated ALT but negative for anti-HCV by ELISA had detectable serum HCV RNA, as compared to eight of 10 anti-HCV ELISA-positive donors (P < 0.0001). However, although negative for HBsAg, 12 of the 65 (18%) had serum HBV DNA by PCR.(ABSTRACT TRUNCATED AT 250 WORDS)

Assembly and composition of the chlorophyll a-b light-harvesting complex of barley (Hordeum vulgare L.): Immunochemical analysis of chlorophyll b-less and chlorophyll b-deficient mutants

The chlorina-f2 mutant of barley (Hordeum vulgare L.) contains no chlorophyll b in its light-harvesting antenna, whereas the chlorina-103 mutant contains approximately 10% of the chlorophyll b found in wild-type. The absolute chlorophyll antenna size for Photosystem-II in wild-type, chlorina-103 and chlorina-f2 mutant was 250, 58 and 50 chlorophyll molecules, respectively. The absolute chlorophyll antenna size for Photosystem-I in wild-type, chlorina-103 and chlorina-f2 mutant was 210, 137 and 150 chlorophyll molecules, respoectively. In spite of the smaller PS I antenna size in the chlorina mutants, immunochemical analysis showed the presence of polypeptide components of the LHC-I auxiliary antenna with molecular masses of 25, 19.5 and 19 kDa. The chlorophyll a-b-binding LHC-II auxiliary antenna of PS II contained five polypeptide subunits in wild-type barley, termed a, b, c, d and e, with molecular masses of 30, 28, 27, 24 and 21 kDa, respectively. The polypeptide composition of the LHC-II auxiliary antenna of PS II was found to be identical in the two mutants, with only the 24 kDa subunit d present at an equal copy number per PS II in each of the mutants and in the wild-type barley. This d subunit assembles stably in the thylakoid membrane even in the absence of chlorophyll b and exhibits flexibility in its complement of bound chlorophylls. We suggest that polypeptide subunit d binds most of the chlorophyll associated with the residual PS II antenna in the chlorina mutants and that is proximal to the PS II-core complex.

Photosystem II Reaction Center Damage and Repair in Dunaliella salina (Green Alga) (Analysis under Physiological and Irradiance-Stress Conditions)

Mechanistic aspects of the photosystem II (PSII) damage and repair cycle in chloroplasts were investigated. The D1/32-kD reaction center protein of PSII (known as the psbA chloroplast gene product) undergoes a frequent light-dependent damage and turnover in the thylakoid membrane. In the model organism Dunaliella salina (green alga), growth under a limiting intensity of illumination (100 [mu]mol of photons m-2 s-1; low light) entails damage, degradation, and replacement of D1 every about 7 h. Growth under irradiance-stress conditions (2000 [mu]mol of photons m-2 s-1; high light) entails damage to and replacement of D1 about every 20 min. Thus, the rate of damage and repair of PSII appears to be proportional to the light intensity during plant growth. Low-light-grown cells do not possess the capacity for high rates of repair. Upon transfer of low-light-grown cells to high-light conditions, accelerated damage to reaction center proteins is followed by PSII disassembly and aggregation of neighboring reaction center complexes into an insoluble dimer form. The accumulation of inactive PSII centers that still contain the D1 protein suggests that the rate of D1 degradation is the rate-limiting step in the PSII repair cycle. Under irradiance-stress conditions, chloroplasts gradually acquire a greater capacity for repair. The induction of this phenomenon occurs with a half-time of about 24 h.

Dynamics of Photosystem Stoichiometry Adjustment by Light Quality in Chloroplasts

Long-term imbalance in light absorption and electron transport by photosystem I (PSI) and photosystem II (PSII) in chloroplasts brings about changes in the composition, structure, and function of thylakoid membranes. The response entails adjustment in the photosystem ratio, which is optimized to help the plant retain a high quantum efficiency of photosynthesis (W.S. Chow, A. Melis, J.M. Anderson [1990] Proc Nat Acad Sci USA 87: 7502-7506). The dynamics of photosystem ratio adjustment were investigated upon the transfer of pea {Pisum sativum} plants from a predominantly PSI-light to a predominantly PSII-light environment and vice versa. The concentration of functional components (primary electron accepting plastoquinone of PSII [QA], P700) and that of constituent proteins were monitored during acclimation by A difference spectrophotometry and immunoblot analysis, respectively. Fully reversible changes in photosystem ratio occurred with a half-time of about 20 h. They involved closely coordinated changes in the concentration of the QA, reaction center protein D1, D2, and the 9-kD apoprotein of the cytochrome b559 for PSII. Similarly, closely coordinated changes in the relative concentration of P700 and reaction center proteins of PSI were observed. The level of chlorophyll b and that of the light-harvesting complex II changed in accordance with the concentration of PSII in the acclimating thylakoids. Overall, adjustments in the photosystem ratio in response to PSI- or PSII-light conditions appeared to be a well-coordinated reaction in the chloroplast. The response was absent in the chlorophyll b-less chlorina f2 mutant of barley (Hordeum vulgare) and in a phycobilisomeless mutant of Agmenellum quadruplicatum, suggesting that photosystem accessory pigments act as the light-quality perception molecules and that PSI and PSII themselves play a role in the signal transduction pathway.