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171.
C. B. Osmond J. A. M. Holtum M. H. O'Leary C. Roeske O. C. Wong R. E. Summons P. N. Avadhani 《Planta》1988,175(2):184-192
The labeling patterns in malic acid from dark 13CO2 fixation in seven species of succulent plants with Crassulacean acid metabolism were analysed by gas chromatography-mass spectrometry and 13C-nuclear magnetic resonance spectrometry. Only singly labeled malic-acid molecules were detected and on the average, after 12–14 h dark 13CO2 fixation the ratio of [4-13C] to [1-13C] label was 2:1. However the 4-C carboxyl contained from 72 to 50% of the label depending on species and temperature. The 13C enrichment of malate and fumarate was similar. These data confirm those of W. Cockburn and A. McAuley (1975, Plant Physiol. 55, 87–89) and indicate fumarase randomization is responsible for movement of label to 1-C malic acid following carboxylation of phosphoenolpyruvate. The extent of randomization may depend on time and on the balance of malic-acid fluxes between mitochondria and vacuoles. The ratio of labeling in 4-C to 1-C of malic acid which accumulated following 13CO2 fixation in the dark did not change during deacidification in the light and no doubly-labeled molecules of malic acid were detected. These results indicate that further fumarase randomization does not occur in the light, and futile cycling of decarboxylation products of [13C] malic acid (13CO2 or [1-13C]pyruvate) through phosphoenolpyruvate carboxylase does not occur, presumably because malic acid inhibits this enzyme in the light in vivo. Short-term exposure to 13CO2 in the light after deacidification leads to the synthesis of singly and multiply labeled malic acid in these species, as observed by E.W. Ritz et al. (1986, Planta 167, 284–291). In the shortest times, only singly-labeled [4-13C]malate was detected but this may be a consequence of the higher intensity and better detection statistics of this ion cluster during mass spectrometry. We conclude that both phosphoenolpyruvate carboxylase (EC 4.1.1.32) and ribulose-1,5-biphosphate carboxylase (EC 4.1.1.39) are active at this time.Abbreviations CAM
Crassulacean acid metabolism
- GCMS
gas chromatography-mass spectrometry
- MS
mass spectrometry
- NMR
nuclear magnetic resonance spectrometry
- PEP
phosphoenolpyruvate
- RuBP
ribulose 1,5-bisphosphate 相似文献
172.
Airway responsiveness to inhaled cholinergic agonist during the early stage of pulmonary O2 toxicity was examined to determine whether normobaric hyperoxia alters airway function. Eight healthy nonsmoking males with moderate base-line methacholine responsiveness breathed normobaric O2 (greater than or equal to 95%) over 12 h and on another occasion breathed air in an identical protocol. Vital capacity, expiratory flow, airway responsiveness to methacholine, and respiratory symptoms were measured at 0, 4, 8, and 12 h while subjects breathed O2 and 12 h afterwards. After 12 h, forced vital capacity was significantly decreased with O2 breathing but not with air breathing. At 4, 8, or 12 h of exposure and 12 h after exposure, there was no difference in methacholine sensitivity or reactivity between O2 and air-exposure trials. The earliest manifestations of pulmonary normobaric O2 toxicity in normal adults include diminished vital capacity and the onset of respiratory symptoms, but early O2 toxicity does not produce altered responsiveness to inhaled methacholine. 相似文献
173.
beta 2-Adrenergic bronchodilator and muscarinic cholinergic bronchoconstrictor agonists both stimulate ciliary activity in vitro. To test the hypothesis that increases in autonomic activity would result in increases in ciliary beat frequency (CBF) in vivo, a correlation analysis heterodyne laser light-scattering system was developed and validated to measure the stimulating effects of sympathomimetic and parasympathomimetic agonists on tracheal CBF in intact, anesthetized beagles. The mean baseline CBF from 42 studies of 274 measurements in 9 (5 male and 4 female) adult beagles was 6.6 +/- 1.1 Hz. The stimulating effects of a beta 2-adrenergic agonist, fenoterol, and a muscarinic cholinergic agonist, methacholine, on CBF were studied on four and eight beagles, respectively. The studies were randomized and blinded. Aerosolized 10(-5) M fenoterol stimulated the CBF from the base line of 6.8 +/- 2.5 to 32.0 +/- 17.9 Hz in four dogs. Aerosolized methacholine stimulated the CBF from the base line of 5.8 +/- 0.7 to 9.4 +/- 3.0 Hz for 10(-8) M, and to 12.6 +/- 3.1 Hz for 10(-6) M in eight dogs. These are the first data obtained in intact animals that demonstrate CBF in the lower respiratory tract is regulated by autonomic agonists. 相似文献
174.
Modulation of the epidermal growth factor receptor by brain-derived growth factor in Swiss mouse 3T3 cells 总被引:3,自引:0,他引:3
Incubation of Swiss mouse 3T3 cells at 37 degrees C with bovine brain-derived growth factor (BDGF) decrease the cell surface 125I-EGF binding activity of these cells by 70-80%. This down-modulation of the EGF receptor by BDGF was time, temperature, and dose dependent. Scatchard plot analysis indicated that BDGF binding led to a selective decrease in the number of high-affinity EGF receptors. The BDGF-induced down-modulation of the EGF receptor was completely blocked by protamine, a potent inhibitor of receptor binding and mitogenic activities of BDGF. BDGF down-modulated the EGF receptor in phorbol myristic acetate (PMA)-pretreated cells, as well as in control cells. Furthermore, PMA-pretreated cells responded mitogenically to BDGF, whereas PMA itself failed to stimulate the mitogenic response of PMA-pretreated cells. This BDGF-induced down-modulation of the EGF receptor in PMA-desensitized cells suggests that BDGF down-regulates the EGF receptor by a mechanism distinct from that of PMA. Incubation of cells with compounds which are known to inhibit pinocytosis blocked the down-modulation induced either by BDGF or by platelet-derived growth factor (PDGF) but had no effect on the PMA-induced down-modulation. Incubation of cells with inhibitors of receptor recycling enhanced the BDGF-induced down-modulation of the EGF receptor. These results suggest that BDGF and PDGF induce down-modulation of the EGF receptor by increasing the internalization of cell surface high-affinity receptors and that the internalization process may not be required for down-modulation induced by PMA. 相似文献
175.
A Mok T Wong O Filgueiras P G Casola D W Nicholson W C McMurray P G Harding F Possmayer 《Biochimie et biologie cellulaire》1988,66(5):425-435
CDPdiacylglycerol pyrophosphatase (E.C. 3.6.1.26) activity has been examined in rat lung mitochondrial and microsomal fractions. While the mitochondrial hydrolase exhibited a broad pH optimum from pH 6-8, the microsomal activity decreased rapidly above pH 6.5. Apparent Km values of 36.2 and 23.6 microM and Vmax values of 311 and 197 pmol.min-1.mg protein-1 were observed for the mitochondrial and microsomal preparations, respectively. Addition of parachloromercuriphenylsulphonic acid led to a marked inhibition of the microsomal fraction but slightly stimulated the mitochondrial activity at low concentrations. Mercuric ions were inhibitory with both fractions. Although biosynthetic reactions utilizing CDPdiacylglycerol require divalent cations, addition of Mg2+, Mn2+, Ca2+, Zn2+, Co2+, and Cu2+ all inhibited the catabolic CDPdiacylglycerol hydrolase activity in both fractions. EDTA and EGTA also produced an inhibitory effect, especially with the mitochondrial fraction. Although addition of either adenine or cytidine nucleotides led to a decrease in activity with both fractions, the marked susceptibility to AMP previously reported for this enzyme in Escherichia coli membranes, guinea pig brain lysosomes, and pig liver mitochondria was not observed. These results indicate that rat lung mitochondria and microsomes contain specific CDPdiacylglycerol hydrolase activities, which could influence the rate of formation of phosphatidylinositol and phosphatidylglycerol for pulmonary surfactant. 相似文献
176.
Clustering of hypervariable minisatellites in the proterminal regions of human autosomes 总被引:42,自引:0,他引:42
Six of the human minisatellites detected by DNA fingerprint probes have been localized by in situ hybridization to human metaphase chromosomes. These hypervariable loci are not dispersed at random in the human genome, but show preferential, though not exclusive, localization to terminal G-bands of human autosomes. Two of the proterminal minisatellites are very closely linked to other variable loci. Sequence analysis of one of these additional minisatellites suggests that the two linked minisatellites arose by independent amplification of different repeat units. The proterminal regions of human autosomes may therefore be rich in minisatellites, analogous to the pseudoautosomal terminal pairing region of human sex chromosomes that is similarly abundant in hypervariable minisatellites. 相似文献
177.
178.
179.
修剪强度对乌桕产量的影响 总被引:5,自引:0,他引:5
对乌桕Sapium sebiferum(L.)Roxb.林进行四种不同强度的修剪试验,结果表明,以中度修剪产量最高,结实性状最好。 相似文献
180.
图论在中国慈姑属数量分类研究中的应用 总被引:1,自引:0,他引:1
.黄德世;.钟扬;.陈家宽 《武汉植物学研究》1988,6(4):405-406
慈姑属(Sagittaria L.)是水生单子叶植物泽泻科(Alismataceae)的一个重要属。近年来,陈家宽等对中国慈姑属进行了系统研究。作者应用聚类分析和主成分分析进行了中国慈姑属的数量分类,取得了良好的效果。由于慈姑属分类性状数目较大,因而在压缩后的三维空间中描述分类群间的距离, 相似文献