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91.
A model is presented of competition between sensory axons for trophic molecules (e.g. a neurotrophin such as NGF), produced in a region of skin small enough to permit their free diffusion throughout it; e.g., a touch dome, or a vibrissal follicle hair sinus. The variables specified are the number of high affinity trophic factor receptors per axon terminal and the concentration of trophic factor in the extracellular space. Previous models of this class predicted the loss of all the axons innervating the region except the one requiring least trophic factor for its maintenance, even with high rates of trophic factor production. In the present model, we have imposed upper limits to axonal growth, thereby introducing new equilibria, and we show by a global analysis using LaSalle's theorem, and also by local analysis, that several axons can then coexist if the rate of production of trophic molecules is sufficiently high. 相似文献
92.
Raj HG Singh I Kohli E Kumari R Gupta G Tyagi YK Kumar A Prasad AK Kaushik NK Olsen CE Watterson AC Parmar VS 《Bioorganic & medicinal chemistry》2003,11(6):1015-1019
The quantitative structure-activity relationship (QSAR) studies conducted by us earlier revealed the cardinal role of the pyran ring carbonyl group in the acetoxy polyphenolic compounds for the acetoxy polyphenol:protein transacetylase (TAase) activity. Hence, an attempt was made to examine whether such substrate analogues of benzopyran acetates which lack in the pyran ring carbonyl group, such as 7-acetoxy-2,3-dihydro-2,2-dimethylbenzopyran (BPA), cetachin pentaacetate (CPA) and hematoxylin pentaacetate (HPA) could inhibit the 7,8-diacetoxy-4-methylcoumarin (DAMC):protein (glutathione-S-transferase) transacetylase activity. These compounds were indeed found to remarkably inhibit the TAase activity in a concentration dependent manner and exerted their inhibitory action very rapidly. Further BPA, CPA and HPA were found to abolish the TAase mediated activation of NADPH cytochrome C reductase as well as the inhibition of liver microsome catalyzed aflatoxin B(1) (AFB(1))-DNA binding by DAMC very effectively. These results strongly suggest that the acetoxybenzopyrans merit as potent inhibitors of TAase. 相似文献
93.
The C-terminal thioesterase domain of the nonribosomal peptide synthetase producing the lipopetide surfactin (Srf TE) retains autonomous ability to generate the cyclic peptidolactone skeleton of surfactin when provided with a soluble beta-hydroxy-butyryl-heptapeptidyl thioester substrate. Utilizing the recently solved crystal structure [Bruner, S. D., et al. (2002) Structure 10, 301-310], the active-site nucleophile, Ser80, was changed to Cys, and the other members of the catalytic triad, Asp107 and His207, were changed to Ala, with the resulting mutants lacking detectable activity. Two cationic side chains in the active site, Lys111 and Arg120, were changed to Ala, causing an increased partitioning of the product to hydrolysis, as did a P26G mutant, mimicking the behavior of lipases. To evaluate recognition elements in substrates used by Srf TE, alterations to the fatty acyl group, the heptapeptide, and the thioester leaving group were made, and the resulting substrates were characterized for kinetic competency and flux of product to cyclization or hydrolysis. Alterations that could be accepted for cyclization were identified in all three parts of the substrate, although tolerance limits for changes varied. In addition, cocrystal structures of Srf TE with dipeptidyl boronate inhibitors were solved, illustrating the critical binding determinants of the substrate. On the basis of the structures and biochemical data, the cyclizing conformation of the surfactin peptide was modeled into the enzyme active site. 相似文献
94.
P. Vain B. Worland M. C. Clarke G. Richard M. Beavis H. Liu A. Kohli M. Leech J. Snape P. Christou H. Atkinson 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1998,96(2):266-271
We have used a genotype-independent transformation system involving particle gun bombardment of immature embryos to genetically
engineer rice as part of a programme to develop resistance to nematodes. Efficient tissue culture, regeneration, DNA delivery
and selection methodologies have been established for elite African varieties (‘ITA212’, ‘IDSA6’, ‘LAC23’, ‘WAB56-104’). Twenty-five
transformed clones containing genes coding for an engineered cysteine proteinase inhibitor (oryzacystatin-IΔD86, OC-IΔD86), hygromycin resistance (aphIV) and β-glucuronidase (gusA) were recovered from the four varieties. Transformed plants were regenerated from all clones and analysed by PCR, Southern
and western blot. Detectable levels of OC-IΔD86 (up to 0.2% total soluble protein) in plant roots were measured in 12 out of 25 transformed rice lines. This level of
expression resulted in a significant 55% reduction in egg production by Meloidogyne incognita.
Received: 4 August 1997 / Accepted: 22 August 1997 相似文献
95.
Hepatic NADPH cytochrome P450 oxidoreductase capable of supporting polysubstrate monooxygenase (PSMO) reactions was purified from microsomes obtained from phenobarbitone (PB) pretreated rhesus monkey. Two preparations of the enzyme purified by affinity and molecular exclusion chromatographic techniques demonstrated specific content of 19.5 and 37.9 nmol cytochrome c reduced/min/mg protein and subunit molecular weight of 66 and 80 kDa, respectively. Both forms supported oxidation of NADPH and reduction of cytochrome c and DCIP but only 80 kDa preparation supported PSMO reactions. The reconstituted system consisted of hepatic P450, NADPH cytochrome P450 oxidoreductase, cytochrome b5 all purified from PB pretreated rhesus monkey and dilauroyl phosphatidylcholine or microsomal lipid. Eighty kDa preparation supported the metabolism of aminopyrine and tolbutamide by hepatic P4502C and erythromycin, ethylmorphine and nifedipine by hepatic P450 3A, respectively. The turnover of these substrates increased in the presence of partially purified cytochrome b5 from the rhesus monkey. To best of our knowledge this is the first report on the purification of monkey hepatic NADPH cytochrome P450 oxidoreductase capable of supporting in vitro PSMO by different isozymes of P450. 相似文献
96.
Parthenin — a sesquiterpene lactone fromParthenium hysterophorus L. is an allelochemical that prevents the germination ofPhaseolus aureus Roxb. cv. ML-5 seeds. The response of the seed has been attributed to the inhibition of the respiratory electron transport ability of its embryo. It has been shown to depend directly not only upon concentration of parthenin, but simultaneously on the duration of exposure of the seeds to the chemical as well. A strong correlation exists between the quantum of the response and the product of the period of exposure and the concentration of parthenin. In order to predict the maximum possible germination ability of the seed exposed for a given period to a given concentration of parthenin, an expression X = 10000 Y3 / [eY/0.31-1] was formulated from the equation X = AY3/[eY/Y0-1], where X represents values of maximum respiratory activity, Y represents the product of concentration and time in units mg cn-3 h, A represents a dimensional constant. The trend and nature of response that is calculated on the basis of formulation coincides with that of measured response through spectrophotometry. 相似文献
97.
The metabolism of the isomeric tri- and tetrachlorobenzene isomers, penta- and hexachlorobenzene was investigated in the rabbit. The major urinary metabolites of the isomeric tri- and tetrachlorobenzenes were identified as the corresponding tri- and tetrachlorophenols whose structures were confirmed by chromatographic analyses. The genesis of the formation of metabolites is discussed in terms of their possible arene oxide intermediates in which the NIH shift of a chlorine atom is observed in the oxidation of many of the isomers. Pentachlorobenzene is metabolized to give both pentachlorophenol and a dechlorination-hydroxylation product which was identified as 2,3,4,5-tetrachlorophenol. The hexachlorobenzene substrate did not give any phenolic metabolites. 相似文献
98.
Absorption of radiation by DNA polymer is calculated for the case of bent polymer chains. The molecule is assumed to be straight except for localized bends. The region between two bends is studied in particular. The vibrational properties of the bends are parameterized by a transmission and a reflection coefficient. A general Green function expression for absorption is studied for various values of the damping rate, as well as the transmission/reflection coefficients. Curves of absorption vs frequency are shown for a number of cases. 相似文献
99.
Acute treatment with delta9-tetrahydrocannabinol [delta9-THC; 0.5 or 1.0 mg/kg b.w. intravenously (i.v.)], the major psychoactive constituent of marijuana, produces a dose-related suppression of pulsatile luteinizing hormone (LH) secretion in ovariectomized rats. To determine whether delta9-THC produces this response by altering neurotransmitter and/or neuropeptide systems involved in the regulation of LH secretion, ovariectomized rats were pretreated with antagonists for dopamine, norepinephrine, serotonin, or opioid receptors, and the effect of delta9-THC on LH release was determined. Pretreatment with the D2 receptor antagonists butaclamol (1.0 mg/kg b.w., intraperitoneally) or pimozide [0.63 mg/kg, subcutaneously (s.c.)], the opioid receptor antagonists naloxone (1-4 mg/kg, i.v.) or naltrexone (2 mg/kg, i.v.), the noradrenergic alpha2-receptor antagonist idazoxan (10 microg/kg, i.v.), or the serotonin 5-HT(1C/2) receptor antagonist ritanserin (1 or 5 mg/kg b.w., i.p.), did not alter delta9-THC-induced inhibition of pulsatile LH secretion. Pretreatment with a relatively high dose of the beta-adrenergic receptor blocker propranolol (6 mg/kg, i.v.) attenuated the ability of the low THC dose to inhibit LH release; however, lower doses of propranolol were without effect. Furthermore, the ability of a relatively nonspecific serotonin 5-HT(1A/1B) receptor antagonist pindolol (4 mg/kg, s.c.) or the specific 5-HT1A receptor antagonist WAY-100635 (1 mg/kg, s.c.) to significantly attenuate THC-induced LH suppression indicates that activation of serotonergic 5-HT1A receptors may be an important mode by which THC causes inhibition of LH release in the ovariectomized rat. 相似文献