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1.
Clifford Hawkins 《BMJ (Clinical research ed.)》1985,290(6484):1816-1817
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Clifford Hawkins 《BMJ (Clinical research ed.)》1983,287(6408):1874-1875
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The gill surface area of 0-group, post-metamorphic Pleuronectes flesus L. was examined using digital image analysis software and expressed in relation to body mass according to the equation log Y=loga+c logW ( a =239·02; c =0·723). The components that constitute gill area, total filament length, interlamellar space and unilateral lamellar area were measured. The measurement of the length of every filament on all eight arches showed that commonly used methods of calculation can lead to an under-estimation of up to 24% of total filament length. Direct measurements of unilateral lamellar area with digital image analysis showed that previously reported gill area data for the same species was over-estimated by as much as 58%. In addition, in this species the neglect of gill pouch asymmetry after metamorphosis, can bring about a 14% over-estimation of total gill area. 相似文献
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Multiple metabolic pools of phosphoinositides and phosphatidate in human erythrocytes incubated in a medium that permits rapid transmembrane exchange of phosphate. 总被引:10,自引:6,他引:4 下载免费PDF全文
1. A Hepes-based medium has been devised which allows rapid Pi exchange across the plasma membrane of the human erythrocyte. This allows the metabolically labile phosphate pools of human erythrocytes to come to equilibrium with [32P]Pi in the medium after only 5 h in vitro. 2. After 5-7 h incubation with [32P]Pi in this medium, only three phospholipids, phosphatidic acid (PtdOH), phosphatidylinositol 4-phosphate (PtdIns4P) and phosphatidylinositol 4,5-bisphosphate (PtdIns4,5P2) are radioactively labelled. The concentrations of PtdIns4P and PtdIns4,5P2 remain constant throughout the incubation, so this labelling process is a reflection of the steady-state turnover of their monoester phosphate groups. 3. During such incubations, the specific radioactivities of the monoesterified phosphates of PtdIns4, PtdIns4,5P2 and PtdOH come to a steady value after 5 h that is only 25-30% of the specific radioactivity of the gamma-phosphate of ATP at that time. We suggest that this is a consequence of metabolic heterogeneity. This heterogeneity is not a result of the heterogeneous age distribution of the erythrocytes in human blood. Thus it appears that there is metabolic compartmentation of these lipids within cells, such that within a time-scale of a few hours only 25-30% of these three lipids are actively metabolized. 4. The phosphoinositidase C of intact human erythrocytes, when activated by Ca2+-ionophore treatment, only hydrolyses 50% of the total PtdIns4,5P2 and 50% of 32P-labelled PtdIns4,5P2 present in the cells: this enzyme does not discriminate between the metabolically active and inactive compartments of lipids in the erythrocyte membrane. Hence at least four metabolic pools of PtdIns4P and PtdIns4,5P2 are distinguishable in the human erythrocyte plasma membrane. 5. The mechanisms by which multiple non-mixing metabolic pools of PtdOH, PtdIns4P and PtdIns4,5P2 are sustained over many hours in the plasma membranes of intact erythrocytes are unknown, although some possible explanations are considered. 相似文献
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Turkey erythrocyte membranes as a model for regulation of phospholipase C by guanine nucleotides 总被引:6,自引:0,他引:6
T K Harden L Stephens P T Hawkins C P Downes 《The Journal of biological chemistry》1987,262(19):9057-9061
Phosphoinositides of human, rabbit, rat, and turkey erythrocytes were radiolabeled by incubation of intact cells with [32P]Pi. Guanosine 5'-O-(thiotriphosphate) (GTP gamma S) and NaF, which are known activators of guanine nucleotide regulatory proteins, caused a large increase in [32P]inositol phosphate release from plasma membranes derived from turkey erythrocytes, but had no effect on inositol phosphate formation by plasma membranes prepared from the mammalian erythrocytes. High performance liquid chromatography analysis indicated that inositol bisphosphate, inositol 1,3,4-trisphosphate, inositol 1,4,5-trisphosphate, and inositol 1,3,4,5-tetrakisphosphate all increased by 20-30-fold during a 10-min incubation of turkey erythrocyte membranes with GTP gamma S. The increase in inositol phosphate formation was accompanied by a similar decrease in radioactivity in phosphatidylinositol 4-phosphate (PIP) and phosphatidylinositol 4,5-bisphosphate (PIP2). GTP gamma S increased inositol phosphate formation with a K0.5 of 600 nM; guanosine 5'-(beta, gamma-imido)trisphosphate was 50-75% as efficacious as GTP gamma S and expressed a K0.5 of 36 microM. Although GTP alone had little effect on inositol phosphate formation, it blocked GTP gamma S-stimulated inositol phosphate formation, as did guanosine 5'-O-(2-thiodiphosphate). Turkey erythrocytes were also shown to express phosphatidylinositol synthetase activity in that incubation of cells with [3H] inositol resulted in incorporation of radiolabel into phosphatidylinositol, PIP, and PIP2. Incubation of membranes derived from [3H]inositol-labeled erythrocytes with GTP gamma S resulted in large increases in [3H] inositol phosphate formation and corresponding decreases in radiolabel in PIP and PIP2. The data suggest that, in contrast to mammalian erythrocytes, the turkey erythrocyte expresses a guanine nucleotide-binding protein that regulates phospholipase C, and as such, should provide a useful model system for furthering our understanding of hormonal regulation of this enzyme. 相似文献
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Anaerobic respiration in the Rhodospirillaceae: characterisation of pathways and evaluation of roles in redox balancing during photosynthesis 总被引:2,自引:0,他引:2
Abstract Recent discoveries relating to pathways of anaerobic electron transport in the Rhodospirillaceae are reviewed. The main emphasis is on the organism Rhodobacter capsulatus ** but comparisons are made with Rhodobacter sphaeroides ** f. sp. denitrificans and Rhodopseudomonas palustris . The known electron acceptors for anaerobic respiration in Rhodobacter capsulatus are trimethylamine- N -oxide (TMAO), dimethyl sulphoxide (DMSO), nitrate and nitrous oxide. In each case respiration generates a proton electrochemical gradient and in some cases can support growth on non-fermentable carbon sources. However, the principal objective of this review is to discuss the possibility that, apart from a role in energy conservation, anaerobic respiration in the photosynthetic bacteria may have a special function in maintaining redox balance during photosynthetic metabolism. Thus the electron acceptors mentioned above may serve as auxiliary oxidants: (a) to maintain an optimal redox poise of the photosynthetic electron transport chain; (b) to provide a sink for electrons during phototrophic growth on highly reduced carbon substrates.
Molecular properties of the nitrate reductase, nitrous oxide reductase and a single enzyme responsible for reduction of TMAO and DMSO are discussed. These enzymes are all located in the periplasm. Electrons destined for all three enzymes can originate from the rotenone-sensitive NADH dehydrogenase but do not proceed through the antimycin- and myxothiazol-sensitive cytochrome b/c1 complex. It is likely, therefor, that the pathways of anaerobic respiration overlap with the cyclic photosynthetic electron transport chain only at the level of the ubiquinone pool. Redox components which might be involved in the terminal branches of anaerobic respiration are discussed. 相似文献
Molecular properties of the nitrate reductase, nitrous oxide reductase and a single enzyme responsible for reduction of TMAO and DMSO are discussed. These enzymes are all located in the periplasm. Electrons destined for all three enzymes can originate from the rotenone-sensitive NADH dehydrogenase but do not proceed through the antimycin- and myxothiazol-sensitive cytochrome b/c
10.
Clifford Hawkins 《BMJ (Clinical research ed.)》1987,294(6566):241-242