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1.
The N-(1-deoxy-D-mannitol-1-yl) and N-(1-deoxy-D-glucitol-1-yl) derivatives of L-valine, L-alanine, L-threonine, and L-leucine were prepared by reductive amination of D-mannose and D-glucose with the appropriate amino acids, in the presence of sodium cyanoborohydride. N epsilon-(1-Deoxy-D-mannitol-1-yl)- and N epsilon-(1-deoxy-D-glucitol-1-yl)-L-lysine were prepared by similar reactions of hexoses with N alpha-tert-butoxycarbonyl and N alpha-benzyloxycarbonyl-L-lysine, followed by removal of the protecting groups. The structures were confirmed by 1H-n.m.r. spectroscopy, which showed that each compound was completely free of its C-2 epimer. The synthetic compounds may be used as reference compounds for the identification of N-(1-deoxyhexitol-1-yl)amino acids formed when N-(1-deoxy-D-fructose-1-yl) groups of nonenzymically glycosylated proteins, of the hemoglobin A1c type, are reduced with sodium borohydride, and the protein is subjected to acid-catalyzed hydrolysis. 相似文献
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Physiological potential for survival of propagules of crassulacean Acid metabolism species 总被引:5,自引:1,他引:4 下载免费PDF全文
Terminal stem joints from three opuntias were detached and maintained for 160 days under natural climatic conditions in the winter and summer. Neither Crassulacean acid metabolism (CAM) nor CAM-idling, as evidenced by a diurnal malate flux, was maintained throughout the two periods; ceasing earlier in the summer period. A 13 to 20% fresh weight loss occurred over the winter period, as opposed to a 30 to 40% loss over the summer period, although tissue water potentials remained above −1.5 megapascals. Chlorophyll and protein contents remained essentially constant in the winter but decreased in the summer. Starch content decreased slightly over the winter but more significantly over the summer. Mucilage content increased slightly in winter and declined slightly in summer. The initiation of rooting was found to be inversely related to spine density and dependent upon orientation and season. Comparison of these data suggest rooting coincided with the cessation of CAM-idling in both climatic periods and was uncoupled from the occurrence of precipitation. The physiological limit for survival of these propagules after detachment was lower than anticipated being of only a few months' duration. 相似文献
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R J Altiere J L Szarek L Diamond 《Journal of applied physiology (Bethesda, Md. : 1985)》1984,57(5):1536-1544
Functional innervation of cat airways smooth muscle was examined in isolated segments of trachea and bronchi using electrical field stimulation (EFS) techniques. Field stimulation caused contraction in tissues at resting tone and biphasic responses (contraction followed by relaxation) in tissues precontracted with 5-hydroxytryptamine (5-HT). Contractions were abolished by 10(-6) M atropine. Inhibitory responses were dependent on impulse voltage, duration, and frequency. At low voltages (less than or equal to 10 V) and pulse durations (less than or equal to 0.3 ms), EFS induced relaxations were abolished by 3 X 10(-6) M tetrodotoxin (TTX). Greater stimulus parameters elicited TTX-resistant relaxations. Pretreatment of the tissues with 10(-6) M propranolol and 10(-5) M guanethidine caused rightward shifts in relaxation frequency-response curves. These findings indicate that cat airways are innervated by excitatory cholinergic, inhibitory adrenergic, and inhibitory nonadrenergic noncholinergic (NANC) nerves. Pretreatment of the tissues with hexamethonium, cimetidine, indomethacin, or nordihydroguaiaretic acid did not affect NANC relaxation responses. It is concluded that NANC inhibitory responses in cat airway smooth muscle are mediated through intrinsic postganglionic nerve fibers and occur independently of histamine H2-receptor activation and without involvement of cyclooxygenase or lipoxygenase products of arachidonic acid metabolism. 相似文献
5.
Summary Photosynthetic responses to light and temperature are compared for two genetically related chromosomal races of Machaeranthera gracilis. The ancestral foothills race occurs in cooler, more mesic environments, while the derived desert race occurs in more arid environments. The desert race exhibited greater rates of net photosynthesis at all levels of irradiance than did plants of the foothills race. This enhancement is due primarily to a greater quantum yield and leaf density. High light pretreatment significantly increased the photosynthetic capacity of the desert race, with little or no effect on the foothills race. Furthermore, the leaf density of the desert race was affected proportionately more than the foothills race by light pretreatment. The desert race also possessed higher stomatal and mesophyll conductances to CO2. Both races exhibited enhanced photosynthetic capacities when grown in a warm thermoperiod (35/25 C), relative to a cool thermoperiod (25/15 C), concomitant with slight increases in leaf density. There was a lack of thermal acclimation for both photosynthesis and respiration of the two races. The greater photosynthetic capactity of the desert race is suggested as an evolutionary modification which could account for invasion into and survival in the sonoran Desert. 相似文献
6.
1,2,3,2',3',4',6'-Hepta-O-acetyl-beta-lactose (4) was coupled with 2,3,6,2',3',4',6'-hepta-O-acetyl-alpha-lactosyl bromide (7) in the presence of Hg(CN)2 to afford 1,2,3,2',3',4',6'-hepta-O-acetyl-6-O-(2,3,6,2',3',4',6'-hepta-O-acetyl-b eta- lactosyl)-beta-lactose (11) which, upon O-deacetylation, gave 6-O-beta-lactosyl-alpha,beta-lactoses (64% from 4). In contrast, the reaction of 7 with benzyl 2,3,2',3',4',6'-hexa-O-acetyl-beta-lactoside in the presence of Hg(CN)2 produced 3,6,2',3',4',6'-hexa-O-acetyl-1,2-O- (2,3,2',3',4',6'-hexa-O-acetyl-1-O-benzyl-beta-lactos-6-yl orthoacetyl)-alpha-lactose (63%) and 3,6,2',3',4',6'-hexa-O-acetyl-1,2-O-(1- cyanoethylidene)-alpha-lactose (27%). The glycosidation of 4 using 2,3,4,6-tetra-O-acetyl-alpha-D-galactopyranosyl bromide in the presence of Hg(CN)2 afforded, after deprotection, 4,6-di-O-beta-D-galactopyranosyl-alpha,beta-D-glucoses (66%). The reaction of 11 with 1,2-di-O-benzyl-(R,S)-glycerols and trimethylsilyl trifluoromethanesulfonate yielded, after deprotection, 1-O-(6-O-beta-lactosyl-beta-lactosyl)-(R,S)-glycerols (18%). Under the same coupling conditions 11 reacted with 2-O-benzylglycerol to form 3-O-acetyl-2-O-benzyl-1-O-[2',3',4',6'-hexa-O-acetyl-6-O-(2,3,6,2',3',4' ,6'- hepta-O-acetyl-beta-lactosyl)-beta-lactosyl]-(R,S)-glycerols (16%). 相似文献
7.
The 13C-chemical shifts and 1JC,H values of two series of carbohydrate oxirane derivatives, namely methyl 2,3-anhydro-ribo- and -lyxofuranosides and methyl 2,3-anhydro-4,6-O-benzylidene-manno- and -allopyranosides have been determined. The assignment of 13C resonances has been established mainly by the examination of the proton-coupled and the selective proton-decoupled spectra. The effect of the oxirane rings on the chemical shifts of β and γ carbon atoms (from the oxirane ring oxygen atom) has been observed. Large 1JC,H values associated with cis CH bonds adjacent to the oxirane rings relative to those of trans counterparts have been found. 相似文献
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JG Hansen W Gao J Dupuis GT O’Connor W Tang M Kowgier A Sood SA Gharib LJ Palmer M Fornage SR Heckbert BM Psaty SL Booth SUNLIGHT Consortium Patricia A Cassano 《Respiratory research》2015,16(1)