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61.
62.
Actin binding proteins that change extent and rate of actin monomer-polymer distribution by different mechanisms 总被引:3,自引:0,他引:3
Weber A 《Molecular and cellular biochemistry》1999,190(1-2):67-74
Actin binding proteins control actin assembly and disassembly by altering the critical concentration and by changing the kinetics of polymerization. All of these control mechanisms in some way or the other make use of the energy of hydrolysis of actin-bound ATP. Capping of barbed filament ends increases the critical concentration as long as ATP hydrolysis maintains a difference in the actin monomer binding constants of the two ends. A further increase in the critical concentration on adding a second cap, tropomodulin, to the other, pointed filament end also requires ATP hydrolysis as described by the model presented here. Changes in the critical concentration are amplified into much larger changes of the monomer pool by actin sequestering proteins, provided their actin binding equilibrium constants fall within a relatively narrow range around the values for the two critical concentrations of actin. Cofilin greatly speeds up treadmilling, which requires ATP hydroysis, by increasing the rate constant of depolymerization. Profilin increases the rate of elongation at the barbed filament end, coupled to a lowering of the critical concentration, only if ATP hydrolysis makes profilin binding to the barbed end independent of its binding constant for actin monomers. 相似文献
63.
Kazuhiko?HOSHIZAKIEmail author Kaoru?NIIYAMA Katsuhiko?KIMURA Tamon?YAMASHITA Yukiko?BEKKU Toshinori?OKUDA Eng Seng?QUAH Nur SUPARDI Md.?Noor 《Ecological Research》2004,19(3):357-363
To clarify consistency in the size of carbon pool of a lowland tropical rainforest, we calculated changes in above-ground biomass in the Pasoh Forest Reserve, Peninsular Malaysia. We estimated the total above-ground biomass of a mature stand using tree census data obtained in a 6-ha plot every 2years from 1994 to 1998. The total above-ground biomass decreased consistently from 1994 (431Mgha–1) to 1998 (403Mgha–1) (1Mg=103 kg). These are much lower than that in 1973 for a 0.2ha portion of the same area, suggesting that the the total above-ground biomass reduction might have been consistent in recent decades. This trend contrasted with a major trend for neotropical forests. During 1994–1998, the forest gained 23.0 and 0.88Mgha–1 of the total above-ground biomass by tree growth and recruitment, respectively, and lost 51.9Mgha–1 by mortality. Overall, the biomass decreased by 28.4Mgha–1 (i.e. 7.10Mgha–1·year–1), which is almost equivalent to losing a 76-cm-diameter living tree per hectare per year. Analysis of positive and negative components of biomass change revealed that deaths of large trees dominated the total above-ground biomass decrease. The forest biomass also varied spatially, with the total above-ground biomass density ranging 212–655Mgha–1 on a 0.2-ha basis (n= 30 subplots, 1998) and 365–440Mgha–1 on a 1ha basis. A large decrease of the total above-ground biomass density (>50Mg per ha per 2years) in several 0.2-ha subplots contributed to the overall decrease in the 6-ha total above-ground biomass. In the present study, we discuss the association between forest dynamics and biomass fluctuation, and the implication for carbon cycling in mature forests with emphasis on forest monitoring and assessments of soil and decomposition systems. 相似文献
64.
Ethanol production from H2 and CO2 by a newly isolated thermophilic bacterium, Moorella sp. HUC22-1 总被引:1,自引:0,他引:1
Sakai S Nakashimada Y Yoshimoto H Watanabe S Okada H Nishio N 《Biotechnology letters》2004,26(20):1607-1612
The thermophilic bacterium, Moorella sp. HUC22-1, newly isolated from a mud sample, produced ethanol from H(2) and CO(2) during growth at 55 degrees C. In batch cultures in serum bottles, 1.5 mM ethanol was produced from 270 mM H(2) and 130 mM CO(2) after 156 h, whereas less than 1 mM ethanol was produced from 23 mM fructose after 33 h. Alcohol dehydrogenase and acetaldehyde dehydrogenase activities were higher in cells grown with H(2) and CO(2) than those grown with fructose. The NADH/NAD(+) and NADPH/NADP(+) ratios in cells grown with H(2) and CO(2) were also higher than those in cells grown with fructose. When the culture pH was controlled at 5 with H(2) and CO(2) in a fermenter, ethanol production was 3.7-fold higher than that in a pH-uncontrolled culture after 220 h. 相似文献
65.
The impact of syntaxin and SNAP-25 cleavage on [3H]noradrenaline ([3H]NA) and [3H]dopamine ([3H]DA) exocytotic release evoked by different stimuli was studied in superfused rat synaptosomes. The external Ca2+-dependent K+-induced [3H]catecholamine overflows were almost totally abolished by botulinum toxin C1 (BoNT/C1), which hydrolyses syntaxin and SNAP-25, or by botulinum toxin E (BoNT/E), selective for SNAP-25. BoNT/C1 cleaved 25% of total syntaxin and 40% of SNAP-25; BoNT/E cleaved 40% of SNAP-25 but left syntaxin intact. The GABA uptake-induced releases of [3H]NA and [3H]DA were differentially affected: both toxins blocked the former, dependent on external Ca2+, but not the latter, internal Ca2+-dependent. BoNT/C1 or BoNT/E only slightly reduced the ionomycin-evoked [3H]catecholamine release. More precisely, [3H]NA exocytosis induced by ionomycin was sensitive to toxins in the early phase of release but not later. The Ca2+-independent [3H]NA exocytosis evoked by hypertonic sucrose, thought to release from the readily releasable pool (RRP) of vesicles, was significantly reduced by BoNT/C1. Pre-treating synaptosomes with phorbol-12-myristate-13-acetate, to increase the RRP, enhanced the sensitivity to BoNT/C1 of [3H]NA release elicited by sucrose or ionomycin. Accordingly, cleavage of syntaxin was augmented by the phorbol-ester. To conclude, our results suggest that clostridial toxins selectively target exocytosis involving vesicles set into the RRP. 相似文献
66.
67.
What determines the intracellular ATP concentration 总被引:1,自引:0,他引:1
Analysis is made of the mechanisms that control the intracellular ATP level. The balance between energy production and expenditure determines the energy charge of the cell and the ratio of [ATP] to the adenylate pool. The absolute ATP concentration is determined by the adenylate pool, which, in its turn, depends on the balance between the rates of AMP synthesis and degradation. Experimental data are discussed that demonstrate an increase in the adenylate pool in response to activation of energy-consuming processes. A hypothesis is proposed according to which variation in the adenylate pool and absolute ATP concentration affords a cell the possibility of additional control over processes fulfilling useful work. A mechanism involved in this regulation is described using human erythrocytes as an example. The hypothesis explains why different metabolic pathways (protein and DNA syntheses, polysaccharide synthesis, and lipid synthesis) use different trinucleotides (GTP, UTP, and CTP, respectively) as an energy source. This allows the cell to independently control these metabolic processes by varying the individual nucleotide pools. 相似文献
68.
69.
Microglial activation is common in several neurodegenerative disorders. In the present study, we used the murine BV-2 microglial cell line stimulated with gamma-interferon and lipopolysaccharide to gain new insights into the effects of endogenously produced NO on mitochondrial respiratory capacity, iron regulatory protein activity, and redox-active iron level. Using polarographic measurement of respiration of both intact and digitonin-permeabilized cells, and spectrophotometric determination of individual respiratory chain complex activity, we showed that in addition to the reversible inhibition of cytochrome-c oxidase, long-term endogenous NO production reduced complex-I and complex-II activities in an irreversible manner. As a consequence, the cellular ATP level was decreased in NO-producing cells, whereas ATPase activity was unaffected. We show that NO up-regulates RNA-binding of iron regulatory protein 1 in microglial cells, and strongly reduces the labile iron pool. Together these results point to a contribution of NO derived from inflammatory microglia to the misregulation of energy-producing reactions and iron metabolism, often associated with the pathogenesis of neurodegenerative disorders. 相似文献
70.
Richard K. Watt Robert J. Hilton D. Matthew Graff 《Biochimica et Biophysica Acta (BBA)/General Subjects》2010