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1.
Jerry W. McClure 《Phytochemistry》1974,13(7):1065-1069
Five-day-old etiolated barley shoots respond to brief illumination with red light by increasing their level of PAL ca 50% within 5 hr. When assayed s 相似文献
2.
The shikimate/arogenate pathway: Link between carbohydrate metabolism and secondary metabolism 总被引:2,自引:0,他引:2
Roy A. Jensen 《Physiologia plantarum》1986,66(1):164-168
3.
We investigated the synthesis and translocation of amino compounds in Parasponia, a genus of the Ulmaceae that represents the only non-legumes known to form a root nodule symbiosis with rhizohia. In the xylem sap of P. andersonii we identified asparagine. aspartate. glutamine, glutamated significant quantities of a non-protein amino acid. 4-methylglutamte(2-amino-4-methylpentanedioic acid). This identification was confirmed by two methods, capillary gas chromatography (GC) electron ionization (El) mass spectrometry (MS) and reverse phase high pressure liquid chromatography (HPLC) analysis of derivatized compounds. In leaf, root and nodule samples from P. andersonii and P. parviflora we also identified the related compounds 4-methyleneglutamate and 4-methyleneglulamine. Using 15N2 labelling and GC-Ms analysis of root nodule extracts we followed N2 fixation and ammonia assimilation in P. andersonii root nodules and observed Label initially in glutamine and subsequently in glutamate, suggesting operation of the glutamine synthetase/glutamine:2-oxoglutarate aminotransferase (GS/GOGAT) pathway. Importantly, we observed the incorporation of significant quantities of 15N into 4-methylglutamate in nodules, demonstrating the de nova synthesis of this non protein amino acid and suggesting a role in the translation of N in symbioticParasponia. 相似文献
4.
G. Kozianowski F. Canganella F. A. Rainey H. Hippe G. Antranikian 《Extremophiles : life under extreme conditions》1997,1(4):171-182
A novel thermophilic spore-forming anaerobic microorganism (strain Ab9) able to grow on citrus pectin and polygalacturonic
acid (pectate) was isolated from a thermal spa in Italy. The newly isolated strain grows optimally at 70°C with a growth rate
of 0.23 h−1 with pectin and 0.12 h−1 with pectate as substrates. Xylan, starch, and glycogen are also utilized as carbon sources and thermoactive xylanolytic
(highest activity at 70°–75°C), amylolytic as well as pullulolytic enzymes (highest activity at 80°–85°C) are formed. Two
thermoactive pectate lyases were isolated from the supernatant of a 300-l culture of isolate Ab9 after growth on citrus pectin.
The two enzymes (lyases a and b) were purified to homogeneity by ammonium sulfate treatment, anion exchange chromatography, hydrophobic chromatography and
finally by preparative gel electrophoresis. After sodium dodecylsulfate (SDS) gel electrophoresis, lyase a appeared as a single polypeptide with a molecular mass of 135 000 Da whereas lyase b consisted of two subunits with molecular masses of 93 000 Da and 158 000 Da. Both enzymes displayed similar catalytic properties
with optimal activity at pH 9.0 and 80°C. The enzymes were very stable at 70°C and at 80°C with a half-life of more than 60
min. The maximal activity of the purified lyases was observed with orange pectate (100%) and pectate-sodium salt (90%), whereas
pectin was attacked to a much lesser extent (50%). The K
m values of both lyases for pectate and citrus pectin were 0.5 g·l−1 and 5.0 g·l−1, respectively. After incubation with polygalacturonic acid, mono-, di-, and tri-galacturonate were detected as final products.
A 2.5-fold increase of activity was obtained when pectate lyases were incubated in the presence of 1 mM Ca2+. The addition of 1 mM ethylenediaminetetraacetic acid (EDTA) resulted in complete inhibition of the enzymes. These heat-stable
enzymes represent the first pectate-lyases isolated and characterized from a thermophilic anaerobic bacterium. On the basis
of the results of the 16S rRNA sequence comparisons and the observed phenotypic differences, we propose strain Ab9 as a new
species of Thermoanaerobacter, namely Thermoanaerobacter italicus sp. nov.
Received: May 25, 1997 / Accepted: June 5, 1997 相似文献
5.
6.
Cell-wall lysing enzymes and products of cell-wall digestion elicit ethylene in citrus 总被引:2,自引:0,他引:2
Ethylene production was induced in Valencia oranges [ Citrus sinensis (L.) Osbcck] by injection of the fungal enzyme mixture Pectolyase ( Aspergillus japonicus ) which contains pectolytic enzymes into the peel. The mixture also stimulated production of 1-aminocyclopropane-1-carboxylic acid (ACC). Cycloheximide partially inhibited the Pectolyase-induced ethylene response. Pectin fragments, resulting from partial acid hydrolysis or Pectolyase digestion, caused an increase in ethylene production when injected into the peel of intact orange fruits. Pectic fragments produced by fungal enzymes are known to be elicitors of phytoalexins and in this study are shown to elicit ethylene in citurs. 相似文献
7.
Phenylalanine Transport Across the Blood-Brain Barrier as Studied with the In Situ Brain Perfusion Technique 总被引:6,自引:5,他引:1
Seiji Momma Masaki Aoyagi Stanley I. Rapoport Quentin R. Smith 《Journal of neurochemistry》1987,48(4):1291-1300
Unidirectional L-phenylalanine transport into six brain regions of pentobarbital-anesthetized rats was studied using the in situ brain perfusion technique. This technique allows both accurate measurements of cerebrovascular amino acid transport and complete control of perfusate amino acid composition. L-Phenylalanine influx into the brain was sodium independent and could be described by a model with a saturable and a nonsaturable component. Best-fit values for the kinetic constants in the parietal cortex equaled 6.9 X 10(-4) mumol/s/g for Vmax, 0.011 mumol/ml for Km, and 1.8 X 10(-4) ml/s/g for KD during perfusion with fluid that did not contain competing amino acids. D-Phenylalanine competitively inhibited L-phenylalanine transport with a Ki approximately 10-fold greater than the Km for L-phenylalanine. There were no significant regional differences in Km, KD, or Ki, whereas Vmax was significantly greater in the cortical lobes than in the other brain regions. L-Phenylalanine influx during plasma perfusion was only 30% of that predicted in the absence of competing amino acids. Competitive inhibition increased the apparent Km during plasma perfusion by approximately 20-fold, to 0.21 mumol/ml. These data provide accurate new estimates of the kinetic constants that describe L-phenylalanine transport across the blood-brain barrier. In addition, they indicate that the cerebrovascular transfer site affinity (1/Km) for L-phenylalanine is three- to 12-fold greater than previously estimated in either awake or anesthetized animals. 相似文献
8.
The action of the herbicide glyphosate [N-(phosphonomethyl)-glycine] on phenolic metabolism and phenylalanine ammonia lyase (PAL; EC 4.3.1.5) activity was investigated in yellow nutsedge (Cyperus esculentus L.). Glyphosate caused significant increases in the amount of total soluble hydroxyphenolics in the three fractions studied (neutral, acid and residual). Qualitative and quantitative differences in relation to these fractions and the amount of applied glyphosate were observed. Most of the phenolic compounds which increased after glyphosate treatment were benzoic acids (gentisic. p -OH-benzoic, salicylic and vanillic). Gentisic acid showed the greatest increase in neutral and acid fractions, being twenty- and four-fold, respectively, of the amount found in the control. PAL activity was not affected by the lowest doses of glyphosate (10−4 and 10−3 M) , but a dramatic decrease in PAL activity was observed after 10−2 M treatment. These findings, together with the low levels of cinnamic acids measured in treated yellow nutsedge plants, suggest that PAL activity is only marginally involved in glyphosate action. Since the herbicidal action probably takes place at 5-enol-pyruvylshikimate-3-P synthase (EC 2.5.1.19), an alternative pathway to PAL in phenolic biosynthesis should be activated yielding benzoic acids. 相似文献
9.
Model of ammonia volatilization from calcareous soils 总被引:2,自引:0,他引:2
A quantitative model of ammonia volatilization from the calcareous soil uppermost 1-cm layer was developed and tested. The
model accounts for the following processes: ammonium-ammonia equilibration in the soil solution, cation exchange between calcium
and ammonium which results in ammonium distribution between soil liquid and solid phases, nitrification of dissolved ammonium,
distribution of ammonia between liquid and gaseous phases and diffusion of gaseous ammonia in the soil air.
The combined effect of various characteristics such as soil pH, cation exchange capacity, water capacity and nitrification
rate on ammonia losses from various soil types have been studied. The model was validated against experimental results of
ammonia losses from different soils for its use as a predicting tool.
The model shows that most of ammonia losses can be explained by the interactive effect of high soil pH and low cation exchange
capacity. Computations show increased ammonia volatilization with decreasing soil water capacity. Increasing fertilizer application
rate has a small effect on percentage of ammonia losses. Increased nitrification rate and shorter “lag” period of nitrification
reduce ammonia losses considerably. Good agreement was obtained between model calculations and experimental results of ammonia
volatilization from 13 soils. 相似文献
10.
Summary Transforming growth factor beta (TGF-) activates ATP citrate lyase in freshly isolated rat liver hepatocytes in a time dependent manner. Maximal stimulation of the enzyme occurred with less than thirty minutes of incubation of the cells with TGF-. The half maximal effect on the enzyme determined in hepatocytes incubated with TGF- for 10 min at 37°C was elicited by TGF- concentrations in the 10–11 – 10–12 M range. The potential role of TGF- stimulation of ATP citrate lyase activity in new membrane synthesis is discussed. 相似文献