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J Barber

Publications and source records attributed to J Barber.

At least 145 records · Page 8Linked to original sources
PubMed1993

Further characterization of the psbH locus of Synechocystis sp. PCC 6803: inactivation of psbH impairs QA to QB electron transport in photosystem 2.

The psbH gene encodes a small protein which copurifies with photosystem 2. In the cyanobacterium Synechocystis sp. PCC 6803, psbH is located upstream of the cytochrome b6-f complex genes petC and petA. In striking contrast, in the genomes of plant chloroplasts, psbH is cotranscribed with petB and petD, encoding the other two major subunits of the cytochrome b6-f complex. We report that in Synechocystis sp. PCC 6803 monocistronic psbH and dicistronic petCA transcripts are probably initiated separately, each from DNA regions bearing some similarity to Escherichia coli sigma 70 promoters. Synechocystis sp. PCC 6803 psbH null mutants were generated by cartridge mutagenesis. Studies using a rapid screening procedure involving in situ complementation showed that the PsbH protein is not absolutely required for the assembly of a functionally active photosystem 2 complex since psbH insertion and deletion strains were able to grow photoautotrophically. The rate of photoautotrophic growth was, however, slower than the wild type, and studies of oxygen evolution, chlorophyll fluorescence, and thermoluminescence indicated that this reduction in growth rate is probably due mainly to an impairment in electron flow from QA to QB. We conclude, therefore, that the PsbH protein is not an absolute requirement for photosystem 2 activity but that it functions to optimize electron flow between the two secondary plastoquinone acceptors by interacting with the QB site on the D1 protein.

Base Sequence↗
PubMed1993

The role of insulin-like growth factors and epidermal growth factor-related peptides in intraovarian regulation in the pig ovary.

The autocrine and paracrine role of the insulin-like growth factors (IGFs) and epidermal growth factor (EGF)-related peptides in pig ovary are reviewed. For convenience, each of these regulatory systems is divided into several interactive components: regulated expression of the growth factors, growth factor reception at the cell surface and intracellular action of the growth factors. In addition, the concept of regulated bioavailability and targeting of growth factors in the extracellular space is developed as an important control locus and area for future study. With regard to the IGF system, these components include two ligands--IGF-I and -II, both expressed in the porcine ovary--and the possibility of three receptors. IGF-I and the type I IGF receptor appear to be the most important in stimulating ovarian function and amplifying hormone action. In addition, the 'set-point' of the ovarian IGF system may be determined by the activity of several IGF-binding proteins (IGFBPs). At least four of these proteins are expressed in the pig ovary. Studies of their regulation and action in ovarian cells indicate that they can function as antagonists to FSH and the IGFs. However, preliminary evidence suggests a more dynamic model in which these proteins may direct the site and timing of IGF effects. There are fewer data on the EGF system. At least four EGF-related peptides are expressed in pig ovaries, but insufficient information is available to predict their physiological regulation. These peptides are potent mitogens for ovarian cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Very high level overexpression of bacterial elongation factor Tu.

The tufA gene, which encodes the bacterial elongation factor Tu of E. coli, was isolated as a 1226 bp DNA fragment using the polymerase chain reaction(1). EcoR1 restriction enzyme digestion sites were incorporated at the 3' and 5' termini of the gene. The tufA gene was ligated into the plasmid vector pUC19 and was sequenced fully. A plasmid shown to contain the tufA gene in the correct orientation with respect to the lac promoter of pUC19 was then used to transform E.coli strain JM105 and expression of EFTu in induced cultures of the resulting clone, JM105 pJBDB01, was measured using a continuous monitoring procedure. The clone was shown to produce up to 95 mg of bacterial elongation factor Tu per litre of cell culture.

Base Sequence↗
PubMed1993

Acceleration-induced effects on baboon blood chemistry.

Gravity-induced loss of consciousness (G-LOC) is known to have occurred in pilots since the early 1920's. Most of the research in this area has shown that G-LOC occurs due to a decrease in cerebral blood pressure and a concomitant reduction in brain perfusion. Since a reduction in cerebral blood flow can cause transient hypoxia, it is important to study the cerebral metabolism during high +Gz exposure. One component of these studies should include measurements of substrate availability and degradative products. In the present study, adult baboons were given multiple high +Gz exposures (2 to 6) using the Armstrong Laboratory human centrifuge. Venous blood was collected by an automatic syringe withdrawal pump before, during and after centrifuge exposures. The concentration of blood gases, glucose and lactate tended to decrease during the centrifuge exposure followed by an increase after the run. Total creatine kinase activity in serum was not significantly altered. These results suggest that during +Gz exposure, anaerobic glycolysis is stimulated resulting in elevated lactate production due to a reduction in cerebral blood flow (CBF). The elevated tissue lactate is released into the central circulation upon resumption of normal CBF (after the termination of centrifuge run). Therefore, the observed decrease in lactate concentration during the run may result from a lag in the release of tissue lactate into the blood due to a reduction in CBF. It is speculated that at high +6 Gz, G-LOC may occur as a protective response to reduce the brain metabolic rate, to maintain energy levels and to prevent severe cellular acidosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Acceleration↗
PubMed1992

Subpicosecond equilibration of excitation energy in isolated photosystem II reaction centers.

Photosystem II reaction centers have been studied by femtosecond transient absorption spectroscopy. We demonstrate that it is possible to achieve good photoselectivity between the primary electron donor P680 and the majority of the accessory chlorins. Energy transfer can be observed in both directions between P680 and these accessory chlorins depending on which is initially excited. After excitation of either P680 or the other chlorins, the excitation energy is observed to equilibrate between the majority of these pigments at a rate of 100 +/- 50 fs-1. This energy-transfer equilibration takes place before any electron-transfer reactions and must therefore be taken into account in studies of primary electron-transfer reactions in photosystem II. We also show further evidence that the initially excited P680 excited singlet state is delocalized over at least two chlorins and that this delocalization lasts for at least 200 fs.

Chloroplasts↗
PubMed1992

Observation of pheophytin reduction in photosystem two reaction centers using femtosecond transient absorption spectroscopy.

Photosystem two reaction centers have been studied using a sensitive femtosecond transient absorption spectrometer. Measurements were performed at 295 K using different excitation wavelengths and excitation intensities which are shown to avoid multiphoton absorption by the reaction centers. Analyses of results collected over a range of time scales and probe wavelengths allowed the resolution of two exponential components in addition to those previously reported [Durrant, J. R., Hastings, G., Hong, Q., Barber, J., Porter, G., & Klug, D. R. (1992) Chem. Phys. Lett. 188, 54-60], plus the long-lived radical pair itself. A 21-ps component was observed. The process(es) responsible for this component was (were) found to produce bleaching of a pheophytin ground-state absorption band at 545 nm and the simultaneous appearance of a pheophytin anion absorption band at 460 nm resulting in a transient spectrum which was that of the radical pair P680+Ph-. This component is assigned to the production of reduced pheophytin. A lower limit of 60% of the final pheophytin reduction was found to occur at this rate. Despite subtle differences in transient spectra, the lifetime and yield of this pheophytin reduction are essentially independent of excitation wavelength within the signal to noise limitations of these experiments. A long-lived species was also observed. This species is produced by those processes which result in the 21-ps component, and it has a spectrum which is found to be independent of excitation wavelength. This spectrum is characteristic of the primary radical pair state P680+Ph-. In addition, a 200-ps component was found which is tentatively assigned to a slow energy-transfer/trapping process. This component was absent if P680 was excited directly and is therefore not integral to primary radical pair formation. Overall, it is concluded that the rate of pheophytin reduction is limited to (21 ps)-1, even when P680 is directly excited.

Fabaceae↗
PubMed1992

Two sites of primary degradation of the D1-protein induced by acceptor or donor side photo-inhibition in photosystem II core complexes.

Depending on experimental conditions we have found that photo-inhibitory treatment of photosystem II (PSII) core complexes, isolated from wheat, can generate two fragments of about 23-24 kDa that contain either the C-terminal or N-terminal regions of the D1-protein. A 24 kDa C-terminal fragment appears when the water splitting reaction is not functional and an electron acceptor is present. This 'donor'-side inhibition also generates an N-terminal fragment of about 10 kDa and is suggested to be due to the cleavage of a peptide bond in the region connecting transmembrane segments I and II of the D1-protein. In contrast, an N-terminal 23 kDa D1-protein fragment is detected when the water splitting reactions of the isolated complex are active, and occurs in the absence of an added electron acceptor. This 'acceptor'-side photo-inhibition also generates a C-terminal fragment of about 10 kDa.

Amino Acid Sequence↗
PubMed1992

Characterisation of photoinduced breakdown of the D1-polypeptide in isolated reaction centres of Photosystem II.

When the isolated reaction centre of Photosystem II, reconstituted with the quinone, 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB), is exposed to photoinhibitory illumination, a D1-polypeptide breakdown product of 24 kDa is detected by immunoblotting. In addition, weaker bands are also detected at 17, 13 and 10 kDa. It is suggested that the 24 kDa D1-polypeptide breakdown product is the same as that first observed in vivo by Greenberg et al. (1987) EMBO J. 6, 2865-2869. Its appearance in isolated Photosystem II reaction centres requires the presence of an electron acceptor, but occurs under both aerobic and anaerobic conditions. In our in vitro experimental system the photoinduced degradation of the D1-polypeptide to the 24 kDa fragment was related to the functional activity of the reaction centre and the enzymatic nature of the proteolysis was characterised by a pH optimum of about 8.0 and by inhibition with proteinase inhibitors, especially the serine-type soybean trypsin inhibitor. The results support our earlier findings (Shipton and Barber (1991) Proc. Natl. Acad. Sci. USA 88, 6691-6695) that the appearance of the light-induced D1-polypeptide breakdown pattern of fragments occurs as a consequence of donor side photoinhibition when highly oxidising species accumulate in the reaction centre and bring about pigment oxidation and degradation. We suggest that it is this selective loss of pigments that induces a conformational change in the D1-polypeptide which triggers its autoproteolytic cleavage.

Blotting, Western↗
PubMed1992

Too much of a good thing: light can be bad for photosynthesis.

Even though light is the ultimate substrate for photosynthetic energy conversion, it can also harm plants. This toxicity is targeted to the water-splitting photosystem II and leads to damage and degradation of the reaction centre D1-polypeptide. The degradation of this very important protein appears to be a direct consequence of photosystem II chemistry involving highly oxidizing radicals and toxic oxygen species. The frequency of this damage is relatively low under normal conditions but becomes a significant problem for the plant with increasing light intensity, especially when combined with other environmental stress factors. However, the plant survives this photoinhibition through an efficient repair system which involves an autoproteolytic activity of the photosystem II complex, D1-polypeptide synthesis and reassembly of active complexes.

Amino Acid Sequence↗
PubMed1992

Inhibition of Water Splitting Increases the Susceptibility of Photosystem II to Photoinhibition.

Photosystem II (PSII)-enriched membrane particles were isolated from peas (Pisum sativum L.) and treated in several different ways to inhibit the water oxidation reactions, but not reaction center function itself, as judged by the light-induced rate of reduction of 2,6-dichlorophenol indophenol with and without the artificial electron donor, diphenyl carbazide. It was shown that such treatments increased the susceptibility of the PSII-enriched membranes to photoinhibition. This trend was further observed if 2,6-dichlorophenol indophenol was present during the illumination with photoinhibitory light. On the other hand, protection against the enhanced photoinhibition was found when the water-splitting activity was reconstituted or when the artificial electron donor diphenyl carbazide was present during the preillumination. The results indicate that irreversible photodamage occurred within the PSII reaction center as a consequence of illumination with strong light and that the rate of this damage was enhanced under conditions that are expected to give rise to a photoaccumulation of oxidizing species such as P680(+) on the donor side of PSII. This mechanism of photoinhibitory damage occurred under both aerobic and anaerobic conditions.

Journal Article↗
PubMed1992

Effect of Cold Treatments on the Binding Stability of Photosystem II Extrinsic Proteins and an Associated Increase in Susceptibility to Photoinhibition.

When pea plants (Pisum sativum L. cv Feltham First) are subjected to freezing conditions (-18 degrees C) followed by a thaw to 18 degrees C, there is a significant inhibition of water-splitting capacity judged by the rate of light-induced reduction of 2,6-dichlorophenol indophenol using isolated thylakoid membrane fragments enriched in photosystem II (PSII). The freeze-thaw-induced inhibition of water-splitting activity has been correlated with the loss of the 17- and 23-kilodalton extrinsic protein of PSII and with a weakening of the binding of the 33-kilodalton protein. There was no apparent loss of bound manganese. Addition of 10 millimolar CaCl(2), however, allowed a full recovery of the water-splitting activity of these modified PSII-enriched particles. The freeze-thaw-induced changes in the organization and functional capacity of PSII was found to increase its susceptibility to photoinhibition in agreement with the concepts presented in the accompanying paper, that oxidative damage can occur within the PSII reaction center as a consequence of extending the lifetime of P680(+).

Journal Article↗
PubMed1992

Longterm drug therapy for rheumatoid arthritis in seven rheumatology private practices: I. Nonsteroidal antiinflammatory drugs.

The probability of continuation of a particular nonsteroidal antiinflammatory drug (NSAID) over 5 years was estimated for 1,775 courses taken by 532 patients with rheumatoid arthritis treated in 7 rheumatology private practices. Similar results were seen for 15 different NSAID--48% of courses were continued at 12 months, 36% at 24 months, and 20% at 60 months. Only acetylated salicylates, other than plain aspirin, were continued significantly longer than any of the other NSAID. The probability of continuation of plain aspirin was similar to other NSAID, including nonacetylated salicylates and nonsalicylate NSAID. The first NSAID taken by an individual patient was continued only marginally longer than the 4th NSAID taken by the same patient. While most NSAID courses were not continued for long periods, 20% were continued for longer than 5 years, suggesting effective longterm results in this minority of courses.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed1991

New evidence suggests that the initial photoinduced cleavage of the D1-protein may not occur near the PEST sequence.

When isolated reaction centres of photosystem 2 from pea or wheat are exposed to photoinhibitory illumination in the presence of an electron acceptor, breakdown products of the D1-protein are observed having molecular masses ranging from about 24 to 10 kDa. By using antibodies raised to the C-terminal or N-terminal portions of D1 it was shown that the major breakdown fragment of 24 kDa was derived from the C-terminus. This conclusion was supported by phosphorylation studies and from the digestion pattern obtained by lysine specific endoprotease-induced proteolysis. The complementary N-terminal breakdown fragment was found to have an apparent molecular mass of 10 kDa. The implications of these data are discussed in terms of the possible relationship between the 24 kDa C-terminal fragment and the 23.5 kDa breakdown fragment detected in vivo by Greenberg et al. [1987, EMBO J. 6, 2865-2869] and it is suggested, based on limited proteolysis using papain, that the latter may not be derived from the N-terminus as previously thought but also originates from the C-terminus.

Blotting, Western↗