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91.
Orientation of the protonated retinal Schiff base group in bacteriorhodopsin from absorption linear dichroism. 总被引:6,自引:4,他引:2 下载免费PDF全文
Linear dichroism experiments are performed on light-adapted bacteriorhodopsin (BR568) films containing native retinal (A1) and its 3,4-dehydroretinal (A2) analogue to measure the angle between the chromophore transition dipole moment and the membrane normal. QCFF/pi calculations show that the angle between the transition moment and the long axis of the polyene is changed by 3.4 degrees when the C3-C4 bond is unsaturated. The difference vector between the two transition moments points in the same direction as the Schiff base (N----H) bond for the all-trans BR568 chromophore. Because the plane of the chromophore is perpendicular to the membrane plane, a comparison of the transition moment orientations in the A1- and A2-pigments enables us to determine the orientation of the N----H bond with respect to the absolute chromophore (N----C5 vector) orientation. The angles of the transition moments are 70.3 degrees +/- 0.4 degrees and 67.8 degrees +/- 0.4 degrees for the A1- and A2-pigments, respectively. The fact that the change in the transition moment angle (2.5 degrees) is close to the predicted 3.4 degrees supports the idea that the chromophore plane is nearly perpendicular to the membrane plane. The decreased transition moment angle in the A2-analogue requires that the N----H bond and the N----C5 vector point toward the same membrane surface. Available results indicate that the N----C5 vector points toward the exterior in BR568. With this assignment, we conclude that the N----H bond points toward the exterior surface and its most likely counterion Asp-212. This information makes possible the construction of a computer graphics model for the active site in BR568. 相似文献
92.
Measurements of small-angle x-ray scattering have been made on films prepared from fine and coarse (i.e., formed at high and low, respectively, pH and ionic strength) clots of bovine fibrin by osmotic shrinkage or compression in one dimension. Intensity profiles were obtained with pinhole geometry on films stretched up to a stretch ratio of 1.43. In unstretched coarse films, repeat spacings were seen at about 245, 120, and 77-80 A. These peaks can probably be identified with the first, second, and third orders of the well-known fibrin repeat of 225 A. In unstretched fine films, only the 77-80 A spacing was seen. In this case, the first two orders may be weak because the half-staggered arrangement of monomer units giving rise to the 225 A reflection is not reinforced by lateral aggregation of protofibrils; the third order may be strong since the molecular subdomains appear to divide the repeat roughly into thirds. After stretching, the 77-80 A spacing persisted in the meridional direction but almost disappeared in the equatorial. Experiments on unstretched films prepared with ancrod substituted for thrombin gave similar results. 相似文献
93.
Preparation and use of N-iodoacetyltyramine in generation of 125I-labeled compounds is described. The kinetics of alkylation of N-acetylcysteine by N-iodoacetyltyramine (k2 = 3.0 M-1 s-1) and N-chloroacetyltyramine (k2 = 0.12 M-1 s-1) indicate that N-iodoacetyltyramine is more useful for labeling sulfhydryl-containing compounds to high specific activity with 125I. Conditions for preparation of carrier-free 125I-labeled N-iodoacetyl-3-monoiodotyramine in 50% yield based on starting iodide are described. The high degree of group specificity of N-iodoacetyl-3-monoiodotyramine reaction with sulfhydryl groups is demonstrated by the high reactivity toward sulfhydryl-containing bovine serum albumin and low reactivity toward N-ethylmaleimide-blocked bovine serum albumin and IgG. 125I-labeled N-iodoacetyl-3-monoiodotyramine was also used to prepare an 125I-labeled ACTH derivative that retains full biological activity, further demonstrating the selectivity toward reactions with sulfhydryl groups. 相似文献
94.
95.
Correction of the N-terminal sequences of the human plastin isoforms by using anchored polymerase chain reaction: identification of a potential calcium-binding domain. 总被引:9,自引:3,他引:6 下载免费PDF全文
Plastins are a family of at least three cytoplasmic protein isoforms that are expressed differentially between cells of the hematopoietic lineages and cells of solid tissues. Expression of the L-plastin isoform appears to be restricted to replicating blood cells, and the two T-plastin isoforms appear to be restricted to replicating cells of solid tissues. However, L-plastin is induced in many human solid tumor-derived cells. We used the anchored polymerase chain reaction technique to amplify and clone the missing 5' ends of plastin mRNAs. We found that both plastin isoforms contain a potential calcium binding site near the N terminus. 相似文献
96.
The arcB gene of Escherichia coli encodes a sensor-regulator protein for anaerobic repression of the arc modulon 总被引:28,自引:2,他引:26
The arcA (dye) and arcB genes of Escherichia coli are responsible for anaerobic repression of target operons and regulons of aerobic function (the arc modulon). The amino acid sequence of ArcA (Dye) indicated that it is the regulator protein of a two-component control system. Here we show that ArcB is a membrane sensor protein on the basis of its deduced amino acid sequence (778 residues), hydropathicity profile, and cellular distribution. On the carboxyl end of the ArcB sequence there is an additional domain showing homology with conserved regions of regulator proteins. Deletion into this domain destroyed ArcB function. ArcB conserved a histidine residue for autophosphorylation of the sensor proteins, and aspartic residues important for the regulator proteins. 相似文献
97.
厦门附近海域浮游甲藻类的分布 总被引:3,自引:0,他引:3
本文报道了厦门附近海域浮游甲藻类49种,并对其生态特性以及与海洋环境因素的关系进行了详细研究与讨论。分析的204号样品,系1980年9月至1981年8月,逐月采自厦门海域的浔江区(Ⅰ区),西港区(Ⅱ区)和九龙江口区(Ⅱ区)。 相似文献
98.
99.
国产磨芋属的染色体核型报道(1) 总被引:4,自引:0,他引:4
本文报道了磨芋属(Amorphophallus Blume)六个种的染色体数目和核型,其中5个种属于首次报道。其核型公式如下: 1.滇磨芋 K(2n)=2x=26=26m.2.磨芋 K(2n)=2x=26=26m.3.攸落磨芋K(2n)=2x=26=22m(2SAT)+4sm.(2SAT).4.西盟磨芋 K(2n)=2x=26=20m+4sm+2st.5.勐海磨芋 K(2n)=2x=26=22m+4sm.6.白磨芋 K(2n)=2x=26=20m(2SAT)+6sm。 相似文献
100.
Summary Variation of DA/DAPI intensity in the Yq12 band was observed in five amniotic cell specimens and one blood specimen from the father of one fetus. Three distinct classes of Yq heterochromatin were identified by distamycin A (DA) treatment of the cell cultures and various staining techniques. The heterochromatin in the Yq11.23 sub-band does not under-condense when exposed to DA, and shows pale fluorescence with quinacrine staining, positive C-banding, and bright fluorescence with DA/DAPI technique. This class of heterochromatin was consistently observed in all specimens studied. The other two classes of heterochromatin are in the Yq12 band. Both show undercondensation when exposed to DA, quinacrine-bright fluorescence, and positive C-banding; howover, one class of heterochromatin shows DA/DAPI-bright fluorescence and the other shows pale fluorescence. The size and banding intensity of the two classes of heterochromatin in Yq12 are variable. These results provide cytological evidence of heterogeneity within the Y heterochromatin region containing AT-rich DNA. 相似文献