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991.
A photoreactive analog of aminopterin, 2′-azidoaminopterin (VI), was synthesized and evaluated as a potential inhibitor and photoaffinity label of folate-utilizing enzymes. The compound was tightly bound to dihydrofolate reductase (DHFR) from escherichia coli (MB 1428) with K1 equal to 3 × 10?11M and to the enzyme from mouse (S-180) cells with K1 approximately equal to 2 × 10?10M. Dissociation constants measured by equilibrium dialysis using radioactive 2′-azidoaminopterin gave a value of KD = 3.2 × 10?9M for the bacterial enzyme. The presence of NADPH enhanced the affinity by more than an order of magnitude. Azidoaminopterin is also an inhibitor of thymidylate synthetase from Lactobacillus casei, competitive with methylene-tetrahydrofolate (Ki 7 × 10?7M). Photolysis of the radioactive inhibitor in complex with DHFR from E. coli led to approximately 3% covalent incorporation of label into protein. The greater part of this attachment was nonspecific as shown by the lack of protection in the presence of methotrexate. Thymidylate synthetase from L. casei was not significantly inactivated upon photolysis in the presence of the inhibitor and deoxyuridylate. Model studies showed that photoreaction of the inhibitor led to covalent linkages with thiol, lysyl amino groups, and the hydroxyl groups of alcohols. Azidoaminopterin may be useful in labeling other enzymes of folate metabolism, although a minor photoproduct reacts nonspecifically with many proteins. The antifolate can be photoconjugated to polylysine as well as to proteins. The polylysine conjugates inhibit DHFR. Difference spectrum analysis of the photoproducts from the irradiation of the DHFR I complex indicates that water reacts efficiently with the enzyme-bound nitrene and must therefore have access to at least part of the bound p-aminobenzoyl group. This analysis suggests that azide analogs of protein ligands may be useful as reporter groups in probing the hydrophobicity of binding sites. 相似文献
992.
Peter A. Lawrence 《Cell》1982,29(2):493-503
The thorax of the adult Drosophila contains about 80 muscles, which develop from the mesoderm. A new genetic marker was used to map the cell lineage of the myoblasts that form these muscles. Clones of marked cells were produced by irradiation of embryos and larvae, and these were detected in the adult by histochemical staining. The principal findings are that the muscles of each segment have separate origins, and that each becomes compartmented precisely into a dorsal-lineage and a ventral-lineage set of muscles, each set probably being formed by the adepithelial cells found in one imaginal disc. In contrast with the epidermis, the muscles of each thoracic segment are not subdivided into anterior and posterior compartments, and clones of muscle cells that are homozygous for recessivelethal alleles of engralled develop normally. 相似文献
993.
Peter Böger 《Physiologia plantarum》1982,54(2):221-224
KCN-treated spinach chloroplasts, their photosystem I being ineffective, exhibit a single reaction site for silicomolybdate. Using this heteropolyanion as electron acceptor, photosynthetic oxygen evolution is partially inhibited by ureas, triazines, or phenylpyridazinone herbicides, their inhibitory effect depending on the concentration of silicomolybate. Labelled atrazine attached to isolated chloroplast material is competitively replaced by silicomolybdate in the same manner as e.g. ureas complete with a triazine herbicide. – It is concluded (1) that silicomolybdate is bound and reduced at the herbicide-binding protein, and (2) that the inhibition of silicomolybdate reduction by herbicides such as DCMU is due to loss of reaction sites for silicomolybdate. 相似文献
994.
The structures of two new triterpene glycosides from Bryonia dioica have been shown, on the basis of chemical and FDMS and 1H and 13C NMR s 相似文献
995.
When dark-grown maize (Zea mays L.) seedlings were exposed to red light (R), Golgi-localized glucan synthetase activity in the mesocotyl began to decrease within 1 h, and fell by approx. 70% in 12 h. The response required at least 10-2 mol m-2 R and saturated at 100 mol m-2. Far-red light (FR) alone inhibited glucan synthetase, and FR reversed the inhibition by R back to the level caused by FR alone. Density gradient fractionation indicated that of the major membrane markers only the Golgi-localized glucan-synthetase activity was affected by R. Golgi-localized latent inosine-diphosphatase activity was unaffected. The kinetics of the response, the photon fluence dependence, and the reversibility by FR all correlated with the inhibition by light of elongation of the mesocotyl, indicating that light inhibits growth and glucan synthetase activity by a similar mechanism.Abbreviations FR
far-red light
- GS
glucan synthetase
- IAA
indole-3-acetic acid
- R
red light 相似文献
996.
Peter J. Davies Eve Emshwiller Thomas J. Gianfagna William M. Proebsting Masana Noma Richard P. Pharis 《Planta》1982,154(3):266-272
The gibberellins (GAs) of both vegetative (leaves and stems) and reproductive (pods and seeds) tissue of the G2 strain of peas Pisum sativum L. were characterized in purified extracts by a combination of sequential silicic-acid partition column chromatography, and gas chromatography-mass spectrometry. Gibberellins A19, A20, A29 and an A29 catabolite were identified in both types of tissue. Gibberellins A9, A17 and A44 were also found in pods and seeds.Abbreviations FID
Ilame ionization detector
- GA(s)
gibberellin(s)
- GC
gas chromatograph(y)
- HPLC
high performance liquid chromatograph(y)
- LD
long day
- MS
mass spectrum(a) or mass spectrometer(ry)
- SD
short day 相似文献
997.
The membranes from the chromoplasts of Narcissus pseudonarcissus L. which are derived from the inner envelope membrane are the site of -carotene synthesis from [1-14C]isopentenyl diphosphate. The enzymes involved are partly peripheral membrane proteins (prenyltransferase, phytoene synthase) and partly integral membrane proteins (cis-trans isomerase, dehydrogenase(s), cyclase(s)). Metabolic channeling is suggested.Abbreviations IPP
isopentenyl diphosphate
- GGPP
geranylgeranyl diphosphate 相似文献
998.
A system for automatic analysis of urinary 3-methylhistidine is described, applying ion-exchange chromatography and using an automatic sample injector, a motoric selector valve, and a diode programmer, which controls the analytical system. The method permits a sampling rate of 22 samples/day. 3-Methylhistidine was completely separated from histidine in 37 min whereas 1-methylhistidine was eluted together with ammonia. The 3-methylhistidine concentration was linear up to 150 nmol/ml and no appreciable sample interaction was found at automatic sequential runs. The error, in a single determination based on duplicate samples, was 4.61% and, in duplicated determinations, 3.26%. The mean urinary 3-methylhistidine output was 299.4 ± 23.8 μmol/day in 12 healthy females and 545.5 ± 35.2 μmol/day in 12 healthy males. The 3-methylhistidine excretion was significantly higher in males than in females, when expressed as the absolute daily output or as the estimated ratio to body weight, body surface area, or creatinine. 相似文献
999.
Colin J. Restall Patrick Williams Michael P. Percival Peter J. Quinn Dennis Chapman 《生物化学与生物物理学报:生物膜》1979,555(1):119-130
A method is reported for the in situ modification of the lipids of isolated spinach chloroplast membranes. The technique is based on a direct hydrogenation of the lipid double bonds in the presence of the catalyst, chlorotris(triphenylphosphine)rhodium (I). The pattern of hydrogenation achieved suggests that the catalyst distributes amongst all of the membranes. The polyunsaturated lipids within the membranes are hydrogenated at a faster rate and at an earlier stage than are the monoenoic lipids.Whilst addition of the catalyst to the chloroplast causes an initial 10–20% decrease in Hill activity, saturation of up to 40% of the double bonds present can be accomplished without causing further significant alterations in photosynthetic electron transport processes or marked morphological changes of the chloroplast structure as observed in the electron microscope. 相似文献
1000.
A system has been established from isolated intact chromoplasts of Narcissus pseudonarcissus flowers that synthesizes geranylgeraniol, an unknown polyprenoid alcohol, phytoene, and -carotene from [1-14C]isopentenyl pyrophosphate in a good yeild. Long chain pyrophosphates are not accumulated. San 6706 inhibits the dehydrogenation of phytoene, whereas nicotine does not lead to an accumulation of lycopene. Separation and identification of polyprenoid lipids was performed by HPLC. The properties and advantages of the chromoplast system are discussed.Abbreviations IPP
isopentenyl pyrophosphate
- TLC
thin-layer chromatography
- HPLC
high pressure liquid chromatography
- GC
gas chromatography
- Sau 6706
4-chloro-5-(dimethylamino)-2-,,-(trifluoro-m-tolyl)3(2H)-pyridazinone 相似文献