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111.
Molecular dynamics simulations have been performed on three phenylimidazole inhibitor complexes ofP450
cam, utilizing the X-ray structures and the AMBER suite of programs. Compared to their corresponding optimized X-ray structures, very similar features were observed for the 1-phenylimidazole (1-PI) and 2-phenylimidazole (2-PI) complexes during a 100 ps MD simulation. The 1-PI inhibitor binds as a Type II complex with the imidazole nitrogen as a ligand of the heme iron. Analysis of the inhibitor-enzyme interctions during the MD simulations reveals that electrostatic interactions of the imidazole with the heme and van der Waals interactions of the phenyl ring with nearby hydrophobic residues are dominant. By contrast, 2-PI binds as a Type I inhibitor in the substrate binding pocket, but not as a ligand of the iron. The interactions of this inhibitor are qualitatively different from that of the Type II 1-PI, being mainly electrostatic/H-bonding interactions with a bound water and polar residues. Although the third compound, 4-PI, in common with 1-PI, also binds as a Type II inhibitor, with one nitrogen of the imidazole as a ligand to the iron, the MD average binding orientation deviates significantly from the X-ray structure. The most important changes observed include: (1) the rotation of the imidazole ring of this inhibitor by about 90° to enhance electrostatic interactions of the imidazole NH group with the carbonyl group of LEU244, and (2) the rotation of the carbonyl group of ASP251 to form a H-bond with VAL254. An analysis of the H-bonding network surrounding this substrate in the optimized crystal structure revealed that there is no H-bonding partner either for the free polar NH group in the imidazole ring of 4-phenylimidazole or for the polar carbonyl group of the nearby ASP251 residue. The deviation of the dynamically averaged inhibitor-enzyme structure of the 4-PI complex from the optimized crystal structure can therefore be rationalized as a consequence of the optimization of the electrostatic interactions among the polar groups. 相似文献
112.
Molecular clones of the mouse t complex derived from microdissected metaphase chromosomes 总被引:27,自引:0,他引:27
Dan Röhme Howard Fox Bernhard Herrmann Anna-Maria Frischauf Jan-Erik Edström Paul Mains Lee M. Silver Hans Lehrach 《Cell》1984,36(3):783-788
Fragments of the proximal half of mouse chromosome 17 including the t-complex region were microdissected from metaphase spreads. DNA was isolated from a pool of such fragments, and was cloned on microscale. Individual clones were used to probe genomic digests of DNA from a pair of Chinese hamster cell lines with or without mouse chromosome 17, and livers of congenic inbred lines of mice carrying wild-type and/or t-haplotype forms of chromosome 17. The data obtained indicate that 95% of the low copy number microclone inserts recognize DNA sequences present on mouse chromosome 17. It has been possible to use one-third of these clones to identify restriction-fragment-length polymorphisms between wild-type and t-haplotype DNA on a congenic background. These results demonstrate that these clones have been derived from the t-complex or regions closely linked to it. Clones of this type should provide starting points for a molecular analysis of this region of the mouse genome. 相似文献
113.
An algorithm for nucleic acid and protein sequence alignment is presented. It is a non-metric local similarity minimal-difference
algorithm and in the current implementation, assembles the matching regions found into a pseudo-global format. Its strengths
are its speed of execution and the especially convenient presentation of its output. The algorithm is intended for use in
sequence melding and local (small-region) similarity searching. It is not designed to replace a metric Needleman-Wunsch-Sellers-type
similarity algorithm. The program is written in FORTRAN and is designed to be easily transportable to a variety of computer
systems. 相似文献
114.
115.
Dan -Eric Nilsson Heimo L. Nilsson 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1981,143(4):503-510
Summary The optical performance of the apposition compound eye of the marine isopodCirolana borealis Lilljeborg (Crustacea) was investigated. The ommatidia comprise large lenses (diam. ca. 150 m), spherical crystalline cones and hypertrophied rhabdoms. The 7 rhabdomeres are fused distally and open proximally. We have designated this rhabdom type as semifused. Distal pigment cells screen neighbouring ommatidia, and a well developed reflecting pigment layer surrounds the rhabdom. The focal length was determined in situ and refractive index measurements, raytracings, and eye mappings were made. The focus was found to lie well below the distal rhabdom tip. A theoretical acceptance function was constructed and a 50% acceptance angle of 45 ° was estimated. The eye parameter (p, according to Snyder 1977) of different ommatidia was between 44 and 14. This together with the anatomy demonstrate an optimation to extremely low light intensities. TheCirolana eye provides an example where acuity is sacrificed for the eye to be able to see at the low light intensities of the inhabitat.The investigation has been supported by a grant from the Swedish Natural Science Research Council (grant no. 2760-103). Our thanks are due to the staff of the marine biological station in Espegrend (Norway). The skilled technical assistance of Miss Inger Norling, Mrs. Rita Wallen, and Miss Maria Walles is gratefully acknowledged. And finally, we would like to express our deep appreciation to Professor Rolf Elofsson for constructive discussions and for his interest and encouragement throughout the investigation. 相似文献
116.
The identification of Tithonia voucher specimens as T. rotundifolia (Mill.) Blake, used for sesquiterpene lactone chemical investigations, have been found to be T. diversifolia (Hemsl.) A. Gray. The compound Ivalin, also is reported for the first time from T. calva Sch. Bip. in Semann. 相似文献
117.
The aminoacyl-tRNA synthetase-tRNA complex: detection by differential labelling of lysine residues involved in complex formation 总被引:2,自引:0,他引:2
The interaction of tRNATyr with tyrosyl-tRNA synthetase from Bacillus stearothermophilus was studied by differential acetylation of lysine residues. The synthetase was trace-labelled in the free form and as the synthetase-tRNATyr complex with [3H]acetic anhydride. In a second step the two 3H-labelled enzyme preparations were fully acetylated with cold reagent under denaturing conditions and were mixed with synthetase that had been homogeneously labelled with excess [14C]acetic anhydride. Peptides containing labelled lysine residues were isolated after chymotryptic digestion and their ratios were determined. These ratios reflect the reactivity of primary amino groups towards acetic anhydride.Involvement of lysine side-chains in complex formation with tRNATyr was suggested from altered ratios. Out of the 22 primary amino groups of tyrosyl-tRNA synthetase at least three showed reduced reactivities towards acetic anhydride in the synthetase-tRNATyr complex by factors of 1.6, 1.9 and 6.8, respectively. The sequences around these lysine residues have been determined enabling their placement when the primary and tertiary structure of the enzyme are available (G. L. E. Koch, to be published). No lysine residue of increased reactivity in the synthetase-tRNATyr complex has been detected.Only one molecule of tRNATyr binds to the dimeric synthetase molecule under the conditions of the differential labelling. If the binding site for the tRNA is on one of the two identical subunits, any observed decrease in chemical reactivity of a particular lysine residue should not exceed a factor of two. The detection of a lysine residue which reacts about seven times more slowly in the synthetase-tRNA complex could therefore indicate that the single binding site is formed by both enzyme subunits. 相似文献
118.
K. L. S. Harley 《Australian Journal of Entomology》1977,16(3):300-300
Key for the Field Identification of Brassica, Potato and Sugar Beet Aphids with Photographic Illustrations: Agricultural Development and Advisory Service, Ministry of Agriculture, Fisheries and Food (Publications) (Tolcarne Drive, Pinner, Middx, HA5 2DT, U.K.). 1977. Pp. 20. Price £3.50 sterling. 相似文献
119.
James W. Wallace Kenneth R. Markham David E. Giannasi John T. Mickel Don L. Yopp Luis D. Gomez J. Dan Pittillo Robert Soeder 《American journal of botany》1982,69(3):356-362
A survey for 1,3,6,7-tetrahydroxy-C-glycosylxanthones of representative species within the primitive vascular plants, emphasizing the leptosporangiate ferns, has indicated a limited distribution of these compounds within three leptosporangiate families: Hymenophyllaceae, Aspleniaceae and Marsileaceae. In the Hymenophyllaceae the distribution of these compounds appears to be a useful criterion for segregating species of Mecodium from other species of Hymenophyllum (sensu lato) and suggests that the tubulate vs. the valvate indusial condition may not be an ideal character for separating all species of Hymenophyllum (s.l.) from those of Trichomanes (s.l.). These compounds appear useful for delimiting several species of Elaphoglossum section Pachyglossa and support a relationship among the Aspleniaceae, Athyriaceae, and Elaphoglossaceae. Their presence in Marsilea also raises questions as to the origin of this group of plants. 相似文献
120.
水生植物叶片的功能性状特征与陆生植物有所不同,同时叶脉类型也显著影响叶片的功能性状。本研究选取9种具有不同叶脉类型的水生植物,通过对叶脉进行直接损伤,分析叶片性状(形态、色素含量和叶绿素荧光指标)在叶脉受损后的变化程度与叶脉类型的关系。结果显示:具有平行脉的3种水生植物对叶脉损伤具有较强的耐受性;具羽状脉的4种植物主脉受损后显著抑制叶片生长,而侧脉受损的影响在不同物种间有所不同,具有物种特异性。本研究可为大型湖泊水生植物修复的水生物种筛选提供参考。 相似文献