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841.
Albert Huff 《Phytochemistry》1982,21(2):261-265
Chlorophyll is effectively bleached by H2O2 in the presence of certain phenols and peroxidase (EC 1.11.1.7) extracted from acetone powders of orange flavedo (Citrus sinensis). Optimal conditions for chlorophyll: hydrogen peroxide oxidoreductase include: pH, 5.9; [H2O2] 222 μM; ionic strength 0.11. A phenol is required and resorcinol is the most effective. Catechol and hydroquinone are inhibitory. Chlorophyll a, chlorophyllide a, and chlorophyll b all have similar Vmax but Km for chlorophyll a is about one-third that of chlorophyll b, while the Km for chlorophyllide a is about one-half that of chlorophyll a. Pheophytin a was much less reactive than chlorophyll a, and Mg2+ included in the reaction system did not affect rates of pheophytin destruction. 相似文献
842.
Effects of crop rotation and fertilization on catalase activity in a soil of the southeastern United States 总被引:2,自引:0,他引:2
Summary Catalase activity of a loamy sand under a 3-year crop rotation in the southeastern U.S.A. was monitored. Corn (Zea mays L.), cotton (Gossypium hirsutum L.), and soybean [Glycine max (L.) Merr.] were the summer crops in the rotation. Winter wheat (Triticum aestivum L.) was planted after corn, and soybean was followed by a winter fallow period. Cotton was followed by a mixture of common vetch (Vicia sativa L.) and crimson clover (Trifolium incarnatum Gibelli & Belli) which was eventually plow-incorporated as a green manure. Highest mean catalase activities were recorded in soil under the wheat, soybean, and winter legume crops; lowest activities were found in soil bearing corn and cotton, and during the winter fallow period. The fertilization regime influenced soil catalase activity independently of the crop. Soil deficient in any of the major elements showed low enzyme activity. Highest activity was found in soil fertilized with P and K, and with N supplied by a winter legume crop. Addition of supplementary mineral nitrogen to this regime reduced catalase activity. Elimination of the winter legume crop from an otherwise complete fertilization regime resulted in a drastic reduction in enzyme activity. In soil receiving a complete fertilization regime there was a close correlation between soil catalase and xylanase activities. A similar correlation between these two enzymes was not found in soil receiving incomplete fertilization. 相似文献
843.
Rhodopseudomonas globiformis is able to assimilate both sulfur moieties of thiosulfate. During growth on 35S-labelled thiosulfate the amino acids cysteine, homocysteine and methionine were labelled. The bulk of thiosulfate, however, was oxidized to tetrathionate and accumulated in the medium. A thiosulfate: acceptor oxidoreductase was partially purified and characterized. The enzyme oxidized thiosulfate to tetrathionate in the presence of ferricyanide. A c-type cytochrome isolated from this organism was reduced by this enzyme. 相似文献
844.
845.
Tudzynski P Hölter K Correia T Arntz C Grammel N Keller U 《Molecular & general genetics : MGG》1999,261(1):133-141
A gene (cpd1) coding for the dimethylallyltryptophan synthase (DMATS) that catalyzes the first specific step in the biosynthesis of ergot
alkaloids, was cloned from a strain of Claviceps purpurea that produces alkaloids in axenic culture. The derived gene product (CPD1) shows only 70% similarity to the corresponding
gene previously isolated from Claviceps strain ATCC 26245, which is likely to be an isolate of C. fusiformis. Therefore, the related cpd1 most probably represents the first C. purpurea gene coding for an enzymatic step of the alkaloid biosynthetic pathway to be cloned. Analysis of the 3′-flanking region of cpd1 revealed a second, closely linked ergot alkaloid biosynthetic gene named cpps1, which codes for a 356-kDa polypeptide showing significant similiarity to fungal modular peptide synthetases. The protein
contains three amino acid-activating modules, and in the second module a sequence is found which matches that of an internal
peptide (17 amino acids in length) obtained from a tryptic digest of lysergyl peptide synthetase 1 (LPS1) of C. purpurea, thus confirming that cpps1 encodes LPS1. LPS1 activates the three amino acids of the peptide portion of ergot peptide alkaloids during D-lysergyl peptide
assembly. Chromosome walking revealed the presence of additional genes upstream of cpd1 which are probably also involved in ergot alkaloid biosynthesis: cpox1 probably codes for an FAD-dependent oxidoreductase (which could represent the chanoclavine cyclase), and a second putative
oxido-reductase gene, cpox2, is closely linked to it in inverse orientation. RT-PCR experiments confirm that all four genes are expressed under conditions
of peptide alkaloid biosynthesis. These results strongly suggest that at least some genes of ergot alkaloid biosynthesis in C. purpurea are clustered, opening the way for a detailed molecular genetic analysis of the pathway.
Received: 26 August 1998 / Accepted: 19 October 1998 相似文献
846.
Cancio I Cajaraville MP 《Biology of the cell / under the auspices of the European Cell Biology Organization》1999,91(8):605-615
The activity and the tissue distribution of the oxygen radical producing enzyme xanthine oxidoreductase (XOR) were measured in the digestive gland of the common marine mussel Mytilus galloprovincialis Lmk along an annual cycle. No xanthine oxidase (XOX) activity could be measured, the enzyme only displaying xanthine dehydrogenase (XDH) activity in all the cases. This is interpreted as a mechanism to avoid the harmful effects of the oxygen radicals that would be produced by XOX during periods following anoxic conditions at low tide. The highest XDH activities coincided with the late spring/early summer months, the activity maxima being recorded from May to July. Histochemically XOR activity was very pronounced in duct and stomach epithelial cells as well as in the surrounding connective tissue and hemolymph vessels, the activity increasing towards the summer months. These seasonal variations in XDH or XOR activities are possibly linked to hormonal changes governing the reproductive cycle and to changes in food availability. The localization of the protein in the connective tissue lining the hemolymph vessels was confirmed immunohistochemically using a polyclonal antibody against rat liver protein that cross-reacted specifically with a polypeptide of 150 kDa of molecular mass in homogenates of the digestive gland. This polypeptide was linked to cytosolic fractions isolated by differential centrifugation from mussel digestive glands. In paraffin sections the antibody labeled the digestive cells of digestive tubules, as well as the connective tissue surrounding the hemolymph vessels, gonadal follicles, digestive epithelia and certain protozoan parasites. Taken together our results suggest that in the digestive gland of bivalve molluscs XOR is involved in the metabolism of purines and in the scavenging of oxygen free radicals. 相似文献
847.
848.
Raja Sterjiades Jeffrey F. D. Dean Gary Gamble David S. Himmelsbach Karl-Erik L. Eriksson 《Planta》1993,190(1):75-87
We have investigated the abilities of extracellular enzymes from dark-grown cell-suspension cultures of sycamore maple (Acer pseudoplatanus L.) to oxidize monolignols, the precursors for lignin biosynthesis in plants, as well as a variety of other lignin-related compounds. Laccase and peroxidase both exist as a multiplicity of isoenzymes in filtrates of spent culture medium, but their abilities to produce water-insoluble, dehydrogenation polymers (DHPs) from the monolignols (in the presence of hydrogen peroxide for the peroxidase reaction) appear identical whether or not the enzymes are purified from the concentrated filtrates or left in a crude mixture. The patterns of bonds formed in these DHPs are identical to those found in DHPs synthesized using horseradish peroxidase or fungal laccase, and many of these bonds are found in the natural lignins extracted from different plant sources. On the other hand, sycamore maple laccase is very much less active on phenolic substrates containing multiple aromatic rings than is sycamore maple peroxidase. We suggst that whereas laccase may function during the early stages of lignification to polymerize monolignols into oligo-lignols, cell-wall peroxidases may function when H2O2 is produced during the later stages of xylem cell development or in response to environmental stresses.Abbreviations DHP
dehydrogenation polymer
- IEF
isoelectric focuring
- NMR
nuclear magnetic resonance
- PAGE
polyacrylamide gel electrophoresis
The authors wish to thank Dr. Masahiro Samejima (University of Tokyo) for provision of lignin model compounds and Dr. Göran Gellerstadt (Royal Institute of Technology, Sweden) for helpful suggestions regarding stilbene formation and light spectroscopy. Monolignols were prepared by Mr. Nate Weymouth with help from Dr. Herb Morrison (USDA/ARS, Richard B. Russell Research Center, Athens, GA). Thanks also to Ms. Izabella Poppe of the Complex Carbohydrate Research Center (CCRC) for assistance with carbohydrate analyses, and Mr. Vincent Sorrentino for help with the growth of cell-suspension cultures. 相似文献
849.
Since the discovery of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced parkinsonism, it has been postulated that (a) MPTP-like toxin(s) such as 1,2,3,4-tetrahydroisoquinoline (TIQ) may induce Parkinson's disease. As the neuronal degeneration in MPTP-induced parkinsonism is thought to be caused by the inhibition of the mitochondrial respiration by 1-methyl-4-phenylpyridinium ion (MPP+), we studied the effects of TIQ-like alkaloids including dopaminederived ones on the mitochondrial respiration using mouse brains. TIQ, tetrahydropapaveroline (THP), and tetrahydropapaverine (THPV) produced significant inhibition of the state 3 and 4 respiration and respiratory control ratio supported by glutamate + malate, the activity of Complex 1 and the ATP synthesis. Among those compounds, THPV was most potent. Toxic properties of these compounds on mitochondria were quite similar to that of MPP+. Our results support the hypothesis that (a) MPTP- or MPP+-like substance(s) may be responsible for the nigral degeneration in Parkinson's disease.Abbreviations used MPTP
1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine
- MPP+
1-methyl-4-phenylpyridinium ion
- ATP
adenosine triphosphate
- ADP
Adenosine diphosphate
- TCL
tricarboxylic acid
- TIQ
cycle: 1,2,3,4-Tetrahydroisoquinoline
- THPV
Tetrahydropapaverine
- THP
Tetrahydropaveroline 相似文献
850.
On the aggregational states of protochlorophyllide and its protein complexes in wheat etioplasts 总被引:8,自引:0,他引:8
Béla Böddi Agneta Lindsten Margareta Ryberg Christer Sundqvist 《Physiologia plantarum》1989,76(2):135-143
The inner membranes from wheat ( Triticum aestivum L. cv. Walde) etioplasts were separated into membrane fractions representative of prolamellar bodies and prothylakoids by differential and gradient centrifugations. The isolated fractions were characterized by absorption-, low-temperature fluorescence-, and circular dichroism (CD) spectroscopy, by high performancy liquid chromatography and by sodium dodecyl sulphate polyacrylamide gel electrophoresis.
The prolamellar body fraction was enriched in NADPH-protochlorophyllide oxidoreductase (E.C. 1.6.99.1), and in protochlorophyllide showing an absorption maximum at 650 nm and a fluorescence emission maximum at 657 nm. Esterified protochlorophyllide was mainly found in the prothylakoid fraction. The carotenoid content was qualitatively the same in the two fractions. On a protein basis the carotenoid content was about three times higher in the prolamellar body fraction than in the prothylakoid fraction. The CD spectra of the membrane fractions showed a CD couplet with a positive band at 655 nm, a zero crossing at 643–644 nm and a negative band at 623–636 nm. These results differ from earlier CD measurements on protochlorophyllide holochrome preparations. The results support the interpretation that protochlorophyllide is present as large aggregates in combination with NADPH and NADPH-protochlorophyllide oxidoreductase in the prolamellar bodies. 相似文献
The prolamellar body fraction was enriched in NADPH-protochlorophyllide oxidoreductase (E.C. 1.6.99.1), and in protochlorophyllide showing an absorption maximum at 650 nm and a fluorescence emission maximum at 657 nm. Esterified protochlorophyllide was mainly found in the prothylakoid fraction. The carotenoid content was qualitatively the same in the two fractions. On a protein basis the carotenoid content was about three times higher in the prolamellar body fraction than in the prothylakoid fraction. The CD spectra of the membrane fractions showed a CD couplet with a positive band at 655 nm, a zero crossing at 643–644 nm and a negative band at 623–636 nm. These results differ from earlier CD measurements on protochlorophyllide holochrome preparations. The results support the interpretation that protochlorophyllide is present as large aggregates in combination with NADPH and NADPH-protochlorophyllide oxidoreductase in the prolamellar bodies. 相似文献