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1.
All plant cells are provided with the necessary rigidity to withstand the turgor by an exterior cell wall. This wall is composed
of long crystalline cellulose microfibrils embedded in a matrix of other polysaccharides. The cellulose microfibrils are deposited
by mobile membrane bound protein complexes in remarkably ordered lamellar textures. The mechanism by which these ordered textures
arise, however, is still under debate. The geometrical model for cell wall deposition proposed by Emons and Mulder (Proc.
Natl. Acad. Sci. 95, 7215–7219, 1998) provides a detailed approach to the case of cell wall deposition in non-growing cells, where there is no evidence for the
direct influence of other cellular components such as microtubules. The model successfully reproduces even the so-called helicoidal
wall; the most intricate texture observed. However, a number of simplifying assumptions were made in the original calculations.
The present work addresses the issue of the robustness of the model to relaxation of these assumptions, by considering whether
the helicoidal solutions survive when three aspects of the model are varied. These are: (i) the shape of the insertion domain,
(ii) the distribution of lifetimes of individual CSCs, and (iii) fluctuations and overcrowding. Although details of the solutions
do change, we find that in all cases the overall character of the helicoidal solutions is preserved. 相似文献
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Pinkerton K. E.; Lewis J.; Mulder A. M.; Ikegami M.; Jobe A. H. 《Journal of applied physiology》1993,74(3):1240-1247
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Ze'ev Barak Bela Ohana Yael Allon Joel Margalit 《Applied microbiology and biotechnology》1987,27(1):88-93
Summary PST, a spontaneous mutant of Bacillus thuringiensis var. israelensis (B.t.i.) resistant to penicillin, streptomycin and tetracycline was isolated by serial selections. In the absence of antibiotics it showed genetic stability for 16 generations. Mosquito larvicidal activity of PST was similar to that of B.t.i., its parental strain. It also maintained the specific antigenicity of B.t.i. although its rate of growth was somewhat lower, a generation time of 55 min for PST vs. 38 min for B.t.i. Cell concentration plays a major role in the phenomenon of PST resistance to penicillin.This antibiotic resistant mutant of b.t.i. provides us with an efficient tool to trace B.t.i. among the indigenous bacteria present in septic habitats in the field as well as inside the larval gut. 相似文献
9.
Arie H. Mulder Francois Hogenboom George Wardeh Anton N. M. Schoffelmeer 《Journal of neurochemistry》1987,48(4):1043-1047
Synaptosomes prepared from rat cerebral cortex and labeled with [3H]noradrenaline (NA) were superfused with calcium-free Krebs-Ringer-bicarbonate medium and exposed to 10 mM K+ plus 0.1 mM Ca2+ so that [3H]NA release was induced. 6,7-Dihydroxy-N,N-dimethyl-2-aminotetralin (TL-99) strongly inhibited synaptosomal K+-induced [3H]NA release (EC50 = 5-10 nM) by activating alpha 2-adrenoceptors. Release was also inhibited (maximally by 40-50%) by morphine (EC50 = 5-10 nM), [Leu5]enkephalin (EC50 = approximately 300 nM), [D-Ala2,D-Leu5]enkephalin (DADLE), and Tyr-D-Ala-Gly-(NMe)Phe-Gly-ol (DAGO) (EC50 values = approximately 30 nM). In contrast to the mu-selective opioid receptor agonists morphine and DAGO, the highly delta-selective agonist [D-Pen2,D-Pen5]enkephalin (1 microM) did not affect [3H]-NA release. Furthermore, the inhibitory effect of DADLE, an agonist with affinity for both delta- and mu-opioid receptors, was antagonized by low concentrations of naloxone. The findings strongly support the view that, like alpha 2-adrenoceptors, mu-opioid receptors mediating inhibition of NA release in the rat cerebral cortex are localized on noradrenergic nerve terminals. 相似文献
10.
Interaction of rat glutathione S-transferases 7-7 and 8-8 with gamma-glutamyl- or glycyl-modified glutathione analogues. 总被引:1,自引:0,他引:1
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A E Adang D J Meyer J Brussee A Van der Gen B Ketterer G J Mulder 《The Biochemical journal》1989,264(3):759-764
Analogues of GSH in which either the gamma-glutamyl or the glycyl moiety is modified were synthesized and tested as both substrates for and inhibitors of glutathione S-transferases (GSTs) 7-7 and 8-8. Acceptor substrates for GST 7-7 were 1-chloro-2,4-dinitrobenzene (CDNB) and ethacrynic acid (ETA) and for GST 8-8 CDNB, ETA and 4-hydroxynon-trans-2-enal (HNE). The relative ability of each combination of enzyme and GSH analogue to catalyse the conjugation of all acceptor substrates was similar with the exception of the combination of GST 7-7 and gamma-L-Glu-L-Cys-L-Asp, which used CDNB but not ETA as acceptor substrate. In general, GST 7-7 was better than GST 8-8 in utilizing these analogues as substrates, and glycyl analogues were better than gamma-glutamyl analogues as both substrates and inhibitors. These results are compared with those obtained earlier with GSH analogues and GST isoenzymes 1-1, 2-2, 3-3 and 4-4 [Adang, Brussee, Meyer, Coles, Ketterer, van der Gen & Mulder (1988) Biochem. J. 255, 721-724] and the implications with respect to the nature of their active sites are discussed. 相似文献