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991.
992.
J Ya MW Markman GT Wagenaar PJ Blommaart AF Moorman WH Lamers 《Canadian Metallurgical Quarterly》1997,249(4):495-505
Tip growth of plant cells has been suggested to be regulated by a tip-focused gradient in cytosolic calcium concentration ([Ca2+]c). However, whether this gradient orients apical growth or follows the driving force for this process remains unknown. Using localized photoactivation of the caged calcium ionophore Br-A23187 we have been able to artificially generate an asymmetrical calcium influx across the root hair tip. This led to a change in the direction of tip growth towards the high point of the new [Ca2+]c gradient. Such reorientation of growth was transient and there was a return to the original direction within 15 min. Root hairs forced to change the direction of their growth by placing a mechanical obstacle in their path stopped, reoriented growth to the side, and grew past the mechanical blockage. However, as soon as the growing tip had cleared the obstacle, growth returned to the original direction. Confocal ratio imaging revealed that a tip-focused [Ca2+]c gradient was always centered at the site of active growth. When the root hair changed direction the gradient also reoriented, and when growth returned to the original direction, so did the [Ca2+]c gradient. This normal direction of apical growth of Arabidopsis thaliana (L.) Heynh, root hairs was found to be at a fixed angle from the root of 85 +/- 6.7 degrees. In contrast, Tradescantia virginiana (L.) pollen tubes that were induced to reorient by touch or localized activation of the caged ionophore, did not return to the original growth direction, but continued to elongate in their new orientation. These results suggest that the tip-focused [Ca2+]c gradient is an important factor in localizing growth of the elongating root hair and pollen tube to the apex. However, it is not the primary determinant of the direction of elongation in root hairs, suggesting that other information from the root is acting to continuously reset the growth direction away from the root surface. 相似文献
993.
994.
Patrick Tortelier 《电信纪事》1995,50(9-10):743-751
The problem of computing the weight distribution of a linear block code is addressed in this paper through the use of the Fourier transforms of indicator functions of parts of a set. After deriving the necessary mathematical formalism, we show that it enables to simply prove again certain known formulas (concerning for instance the Krawtchouk polynomials) and besides to derive two results we believe to be new. First, a recursion formula on polynomials enables direct computation of the weight enumerator of the code in terms of its parity-check matrix. Second, since this formula leads in any case to cumbersome calculations, we derive analytical formulas concerning average weight estimates, together with an estimate of their precision. 相似文献
995.
A simplified procedure was developed for purification of listeriolysin O (LLO) of Listeria monocytogenes, consisting of hydroxylapatite adsorption chromatography followed by Sepharose S ion exchange chromatography. The LLO (58 kDa) appeared pure in terms of sodium dodecylsulfate polyacrylamide electrophoresis and immunoblots with polyclonal rabbit immune sera. The purified LLO could be stored at -65 degrees C for 1 year without loss of immunoreactivity. Similarly, flat-bottom microtiter strips from two vendors that had been charged with LLO, could be stored at -65 degrees C for up to 3 months without loss of LLO. Three patients with documented listeriosis developed elevated IgG titres against LLO; 2 of the patients revealed minimally raised IgM titres, as determined with the enzyme-linked immunosorbent assay. 相似文献
996.
997.
998.
WH Gough S VanOoteghem T Sint NY Kedishvili 《Canadian Metallurgical Quarterly》1998,273(31):19778-19785
We report the cDNA sequence and catalytic properties of a new member of the short chain dehydrogenase/reductase superfamily. The 1134-base pair cDNA isolated from the human liver cDNA library encodes a 317-amino acid protein, retinol dehydrogenase 4 (RoDH-4), which exhibits the strongest similarity with rat all-trans-retinol dehydrogenases RoDH-1, RoDH-2, and RoDH-3, and mouse cis-retinol/androgen dehydrogenase (=73% identity). The mRNA for RoDH-4 is abundant in adult liver, where it is translated into RoDH-4 protein, which is associated with microsomal membranes, as evidenced by Western blot analysis. Significant amounts of RoDH-4 message are detected in fetal liver and lung. Recombinant RoDH-4, expressed in microsomes of Sf9 insect cells using BacoluGold Baculovirus system, oxidizes all-trans-retinol and 13-cis-retinol to corresponding aldehydes and oxidizes the 3alpha-hydroxysteroids androstane-diol and androsterone to dihydrotestosterone and androstanedione, respectively. NAD+ and NADH are the preferred cofactors, with apparent Km values 250-1500 times lower than those for NADP+ and NADPH. All-trans-retinol and 13-cis-retinol inhibit RoDH-4 catalyzed oxidation of androsterone with apparent Ki values of 5.8 and 3.5 microM, respectively. All-trans-retinol bound to cellular retinol-binding protein (type I) exhibits a similar Ki value of 3.6 microM. Unliganded cellular retinol-binding protein has no effect on RoDH activity. Citral and acyclic isoprenoids also act as inhibitors of RoDH-4 activity. Ethanol is not inhibitory. Thus, we have identified and characterized a sterol/retinol-oxidizing short chain dehydrogenase/reductase that prefers NAD+ and recognizes all-trans-retinol as substrate. RoDH-4 can potentially contribute to the biosynthesis of two powerful modulators of gene expression: retinoic acid from retinol and dihydrotestosterone from 3alpha-androstane-diol. 相似文献
999.
1000.
In this paper, a high resolution technique for estimating DOAs of spatially close source signals is presented. It is observed that the array manifold over a sector of interest is rank deficient and the dimension of the array manifold space, which is the range space of the array manifold, is less than the number of sensors in the array. The true signal subspace is a subspace in the array manifold space. A novel technique is provided that searches for the signal subspace in this array manifold space. The resulting estimated signal subspace has minimum principal angles with the data signal subspace generated by eigen-decomposing the covariance matrix of the array data vector. It is proved that the proposed estimator is asymptotically consistent and the estimated signal subspace is closer to the true signal subspace than the data signal subspace formed by MUSIC. The proposed novel technique has better performance than the MUSIC algorithm. Its performance is comparable to MLE and MD-MUSIC yet it requires only one-dimensional searches and is computationally much less intense. Simulation results are presented to show the effectiveness of the proposed technique, and comparisons with MUSIC, MLE, and MD-MUSIC algorithms are also included.This research was supported by TRIO and NSERC. 相似文献