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91.
Glycine decarboxylase is confined to the bundle-sheath cells of leaves of C3−C4 intermediate species
Christopher M. Hylton Stephen Rawsthorne Alison M. Smith D. Alan Jones Harold W. Woolhouse 《Planta》1988,175(4):452-459
Immunogold labelling has been used to determine the cellular distribution of glycine decarboxylase in leaves of C3, C3–C4 intermediate and C4 species in the genera Moricandia, Panicum, Flaveria and Mollugo. In the C3 species Moricandia foleyi and Panicum laxum, glycine decarboxylase was present in the mitochondria of both mesophyll and bundle-sheath cells. However, in all the C3–C4 intermediate (M. arvensis var. garamatum, M. nitens, M. sinaica, M. spinosa, M. suffruticosa, P. milioides, Flaveria floridana, F. linearis, Mollugo verticillata) and C4 (P. prionitis, F. trinervia) species studied glycine decarboxylase was present in the mitochondria of only the bundle-sheath cells. The bundle-sheath cells of all the C3–C4 intermediate species have on their centripetal faces numerous mitochondria which are larger in profile area than those in mesophyll cells and are in close association with chloroplasts and peroxisomes. Confinement of glycine decarboxylase to the bundle-sheath cells is likely to improve the potential for recapture of photorespired CO2 via the Calvin cycle and could account for the low rate of photorespiration in all C3–C4 intermediate species.Abbreviation and symbol kDa
kilodaltons
-
CO2 compensation point 相似文献
92.
Summary The relative hydraulic conductivities of major and minor longitudinal veins, and the apoplastic permeability of the bundle sheaths surrounding all longitudinal and transverse veins were investigated in representatives of the C3, C4/NAD-ME, C4/NAD-ME/PCK intermediate, C4/PCK and C4/NADP-ME photosynthetic types. Using the Hagen-Poiseuille equation and measurements of tracheary element diameters, the number of elements in each vein type and the numbers of each vein type, we calculated that 87–99% of the water flow in a longitudinal direction would be expected to occur in the major veins. The permeability of the mestome sheaths and parenchymatous bundle sheaths surrounding the veins was tested using the negatively-charged, fluorescent dye, trisodium 3-hydroxy-5,8,10-pyrenetrisulfonate (PTS). This dye proved nontoxic to plant tissue at a concentration of 0.5%, according to a deplasmolysis test with onion epidermal strips. The PTS concentration achieved in the tested grass leaves was about 0.035%, well below the toxic limit. When a solution of PTS was fed to the leaves by means of a basal cut, the dye moved into the veins of all orders. From there, it moved outward into the surrounding tissues, indicating that the sheaths surrounding the veins of all orders in all species tested were permeable. Therefore, contrary to previous predictions based on structural observations and some tracer studies, bundle sheaths with suberized cell walls do not function as endodermal layers. 相似文献
93.
The leaf ultrastructure of NADP-malic enzyme type C4 species possessing different anatomical features in the Cyperaceae was examined: types were the Rhynchosporoid type, a normal
Kranz type in which mesophyll cells are adjacent to Kranz cells, and Fimbristyloid and Chlorocyperoid types, unusual Kranz
types in which nonchlorophyllous mestome sheath intervenes between the two types of green cells. They show structural characteristics
basically similar to the NADP-malic enzyme group of C4 grasses, that is, centrifugally located chloroplasts with reduced grana and no increase of mitochondrial frequency in the
Kranz cells. However, the Kranz cell chloroplasts of the Fimbristyloid and Chlorocyperoid types exhibit convoluted thylakoid
systems and a trend of extensive development of peripheral reticulum, although those of the Rhynchosporoid type do not possess
such particular membrane systems. The suberized lamella, probably a barrier for CO2 diffusion, is present in the Kranz cell walls of the Rhynchosporoid type and in the mestome sheath cell walls of the other
two types, and tightly surrounds the Kranz cells (sheaths) that are the sites of the decarboxylation of C4 acids. These ultrastructural features are discussed in relation to C4 photosynthetic function. 相似文献
94.
95.
Koji Sode Nobuaki Hori Yoichi Mikami Isao Karube 《Biocatalysis and Biotransformation》1988,2(1):51-57
Asymmetric reduction of 2,6,6,-trimethyl-2-cyclohexene-l,4-dione (4-oxoisophrone) to (6R)-2,2,6-trimethyl-1,4-cyclohexane-dione((3R)-dihydro-4-oxoisophorone) was catalysed by immobilized thermophilic bacteria, Thermomonospora curvata JTS 321. Because of leakage of entrapped cells from gel beads during reactions using culture medium, we optimized the medium to allow the microbial conversion under conditions of controlled cell growth. Of the media screened, liver infusion medium was found to be the most suitable and microbial conversion was achieved without cell leakage from the immobilized gels. Immobilized T. curvata cells were repeatedly used for the asymmetric reduction of 4-oxoisophorone, more than 15 times, with an extent of conversion of 50%. 相似文献
96.
马齿苋叶片PEPCase由四个相同的亚基组成,亚基分子量为83kD。远紫外CD光谱分析表明,此酶含有36.6%α—螺旋结构。马齿苋叶片PEPCase可被G6P激活,但不能被Gly、Ser激活。G6P可防止酶的尿素变性和枯草杆菌蛋白酶的作用。这种保护效应与G6P诱导的酶构象变化有关。 从酶对低温、高温及尿素的反应来看,马齿苋叶片PEPCase的稳定性高于高粱叶片PEP—Case,两者的免疫特性和电泳特性亦不同。 相似文献
97.
Heng Xu John S. Partilla Brian R. de Costa Kenner C. Rice Richard B. Rothman 《Peptides》1992,13(6):1207-1213
Recent pharmacological data strongly support the hypothesis of δ receptor subtypes as mediators of both supraspinal and spinal antinociception (δ1 and δ2 receptors). In vitro ligand binding data, which are fully supportive of the in vivo data, are still lacking. A previous study indicated that [3H][
-Ala2,
-Leu5]enkephalin labels two binding sites in membranes depleted of μ binding sites by pretreatment with the site-directed acylating agent, 2-(p-ethoxybenzyl)-1-diethylaminoethyl-5-isothiocyanatobenzimidazole-HCI (BIT). The main goal of the present study was to develop a ligand-selectivity profile of the two δncx binding sites. The data indicated that naltrindole and oxymorphindole were relatively selective for site 1 (20-fold). [
-Ser2,Thr6]Enkephalin and deltorphin-II were only 2.7-fold and 2.2-fold selective for site 1. [
-Pen2,
-Pen5]Enkephalin and deltorphin-I were 80-fold and 38-fold selective for site 2.3-Iodo-Tyr-
-Ala-Gly-Phe-
-Leu was 52-fold selective for site 1. Morphine had moderate affinity for site 1 (Ki = 16 nM), and was about 11-fold selective for site 1. Thus, of the 10 drugs studied, only DPDPE and DELT-I were selective for site 2. Viewed collectively with other data, it is likely that the δ1 receptor and the δncx binding site are synonymous. 相似文献
98.
A soluble Lewis blood-group gene associated -3/4-L-fucosyltransferase has been purified from human milk by a series of steps involving hydrophobic chromatography on Phenyl Sepharose 4B, ion exchange chromatography on CM-Sephadex C-50, affinity chromatography on GDP-hexanolamine Sepharose 4B and gel filtration on Sephacryl S-200. The first step separated -3-L-fucosyltransferase activity directed towardsN-acetylglucosamine in Type 2 (Gal1-4GlcNAc-R) acceptors from an -3/4-fucosyltransferase fraction acting on both Type 1 (Gal1-3GlcNAc-R) and Type 2 acceptors. Further purification of this latter fraction on CM-Sephadex and GDP-hexanolamine Sepharose gave a single peak of fucosyltransferase activity that catalysed the addition of fucose toN-acetylglucosamine in both Type 1 and Type 2 acceptors and to theO-3 position of glucose in lactose-based oligosaccharides. The enzyme preparation at this stage resembled previously described -3/4-fucosyltransferase preparations purified from human milk. However, gel filtration of this preparation on Sephacryl S-200 or Sephadex G-150 separated further amounts of -3-fucosyltransferase activity acting solely on Type 2 acceptors and left a residual -3/4-fucosyltransferase that retained strong -4 activity with the Type 1 acceptor, lacto-N-biose 1, and -3 activity with 2-fucosyllactose, but had relatively little -3 activity withN-acetyllactosamine and virtually no capacity to transfer fucose to glycoproteins withN-linked oligosaccharide chains having unsubstituted terminal Type 2 structures. 相似文献
99.
Chronic treatment of hamsters with estradiol for several months has previously been shown to decrease the specific content
of cytochrome P450 in the kidney, a target of hormonal carcinogenesis, but not in liver. The reason for this decrease in metabolic
enzyme activity is unknown and has been examined in this investigation. We now report that the decrease in specific content
of renal cytochrome P450 by 73% in response to estradiol was not affected by co-treatment with tamoxifen for 1 month. The
subcutaneous infusion of 250 μg/day estradiol for 7 days lowered renal cytochrome P450 by 71% from control values and was
therefore used for further mechanistic studies. This treatment decreased renal activities of estradiol 2- or 4-hydroxylase
by 77 to 80%, of 7-ethoxycoumarin-O-deethylase by 66% of control values, respectively, and completely eliminated aryl hydrocarbon
hydroxylase activities, whereas liver enzymes remained unaffected. After 7 days of infusion of estradiol, fluorescent products
of lipid peroxidation were more than doubled in hamster kidney but remained unchanged in liver. The possibility of enzyme
destruction by binding of estradiol 2,3-quinone to metabolizing enzymes was investigatedin vitro. In the presence of 2-hydroxyestradiol, cumene hydroperoxide, and microsomes, conditions known to favor the oxidation of
the steroid to quinone, the binding of catechol estrogen metabolite to microsomal protein increased 60 fold over control values
in the absence of cofactor. Purified rat liver cytochrome P450c also oxidized 2-hydroxyestradiol to 2,3-estradiol quinone.
The rate of oxidation was linear for the first 2–3 min, but thereafter decreased with time. Under these incubation conditions,
irreversible binding of catechol estrogen metabolite to cytochrome P450c increased for the first 2–3 min and then remained
at this plateau level. It was concluded that enzyme destruction by a reactive estrogen metabolite or by lipid peroxides may
be a major reason for the organ-specific decrease in cytochrome P450 enzymes in kidneys of estrogen-treated hamsters. 相似文献
100.
J. L. Tholozan J. P. Touzel E. Samain J. P. Grivet G. Prensier G. Albagnac 《Archives of microbiology》1992,157(3):249-257
Strain X4 was isolated several years ago from an anaerobic mesophilic plant treating vegetable cannery waste waters. It was the first example of propionic fermentation from ethanol. Morphologic and physiologic characterizations of the strain are presented here. This strain is described as type strain of a new species, Clostridium neopropionicum sp. nov. Whole cells of strain X4 ferment [1-13C]ethanol and CO2 to [2-13C]propionate, [1-13C]acetate and [2-13C]propanol, suggesting the absence of a randomizing pathway during the propionate formation. Enzymes involved in this fermentation were assayed in cell-free extracts of cells grown with ethanol as sole substrate. Alcohol dehydrogenase, aldehyde dehydrogenase, phosphate acetyl transferase, acetate kinase, pyruvate synthase, lactate dehydrogenases, and the enzymes of the acrylate pathway were detected at activities sufficient to be involved in ethanol fermentation. The same pathway may be used for the degradation of lactate or acrylate to acetate. 相似文献