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Deoxyribonuclease I (DNase I) is an actin monomer-sequestering actin binding protein (ABP) that inhibits the rate and extent of actin polymerisation in vitro by forming a high affinity, stoichiometric 1:1 complex. Using capillary zone electrophoresis (CZE), we have studied the interaction between G-actin and DNase I to evaluate the capability of CZE to determine the dissociation constant (K(d) value) for this interaction. We used (i) an uncoated fused-silica capillary and ultraviolet (UV) detection at 214 nm; (ii) a hydrophilic-coated capillary with UV detection at 214 nm; and (iii) a hydrophilic-coated capillary with laser-induced fluorescence (LIF) detection. Using procedure (ii), a K(d) value of approximately 0.03 microM was obtained by simulation of binding data. We conclude that CZE combined with a LIF detector has the capacity to extend the determination of K(d) values from the micromolar range to the nanomolar range. Subsequent determination of K(d) values for other actin-binding proteins should provide information on interactions between the binding sites on actin for these proteins and their spatial relationship.  相似文献   
63.
A major portion of the over expressed yeast mitochondrial aconitase, a large 82 kDa monomeric TCA cycle enzyme, in Escherichia coli led to the formation of inclusion bodies. Bacterial chaperonin GroEL mediated the correct folding of aconitase with the assistance of its co-chaperonin GroES in an ATP dependent manner. Till date the chaperonin assisted folding of aconitase was limited to the shake flask studies with relatively low yields of folded aconitase. No attempt had yet been made to enhance the yield of chaperone mediated folding of aconitase using a bioreactor. The current report deals with the effect of co-expression of GroEL/GroES in the production of soluble, biologically active recombinant aconitase in E. coli by cultivation in a bioreactor at different temperatures under optimized conditions. It revealed that the yield of functional aconitase was enhanced, either in presence of co-expressed GroEL/ES or at low temperature cultivation. However, the outcome from the chaperone assisted folding of aconitase was more pronounced at lower temperature. A 3-fold enhancement in the yield of functional aconitase from the bioreactor based chaperone assisted folding was obtained as compared to the shake flask study. Hence, the present study provides optimized conditions for increasing the yield of functional aconitase by batch cultivation in a bioreactor.  相似文献   
64.
Ethylene glycol retention method, standardised by Dyal and Hendricks for clays and soils, has been used for determining specific surface areas of a large variety of adsorbent carbons differing widely in the extent as well as chemical nature of their surfaces. The proposed method yields values comparable with those obtained by the gaseous adsorption methods, irrespective of the oxygen contents of the carbons. A small amount of oxygen, probably within 0.2%, is essential to bring about proper wetting of the carbon by glycol.  相似文献   
65.
The kinetics of polarographic reduction of Co(II) and Ni(II) has been investigated in the presence of increasing concentration of complex forming agent viz ?-caprolactam at pH 6.2 under constant ionic strength. In both the cases the waves were found to be diffusion controlled and irreversible. The values of the kinetic parameters αna and k0f, h have been calculated as a function of the ligand concentration. The polarographic wave was precisely proportional to the concentration up to 3.5 mM of the metal ions. Hence the straight line is useful as a calibration curve in quantitative analysis of these two metal ions. The error does not exceed more than ± 0.2% in any case.  相似文献   
66.
ADP and thrombin are two of the most important agonists of platelet aggregation--a cellular response that is critical for maintaining normal hemostasis. However, aberrant platelet aggregation induced by these agonists plays a central role in the pathogenesis of cardiovascular and cerebrovascular diseases. Agonist-induced primary or secondary activation of phospholipases leads to generation of the second messengers that participate in biochemical reactions essential to a number of platelet responses elicited by ADP and thrombin. Phospholipase A2 (PLA2) has been linked to cardiovascular diseases. However, the mechanism(s) of activation of PLA2 in platelets stimulated by ADP and thrombin has remained less well defined and much less appreciated. The purpose of this review is to examine and compare the molecular mechanisms of activation of PLA2 in platelets stimulated by ADP and thrombin.  相似文献   
67.
The satisfiability problem (SAT) is a fundamental problem in mathematical logic, constraint satisfaction, VLSI engineering, and computing theory. Methods to solve the satisfiability problem play an important role in the development of computing theory and systems. In this paper, we give a BDD (Binary Decision Diagrams) SAT solver for practical asynchronous circuit design. The BDD SAT solver consists of a structural SAT formula preprocessor and a complete, incremental SAT algorithm that is able to find an optimal solution. The preprocessor compresses a large size SAT formula representing the circuit into a number of smaller SAT formulas. This avoids the problem of solving very large SAT formulas. Each small size SAT formula is solved by the BDD SAT algorithm efficiently. Eventually, the results of these subproblems are integrated together that contribute to the solution of the original problem. According to recent industrial assessments, this BDD SAT solver provides solutions to the practical, industrial asynchronous circuit design problems.This research is supported in part by the 1993 ACM/IEEE Design Automation Award, by the Alberta Microelectronics Graduate Scholarship, by the NSERC research grant OGP0046423, and was supported in part by the NSERC strategic grant MEF0045793.Presently, Jun Gu is on leave with the Department of Computer Science, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong.  相似文献   
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A theory is presented for the analysis of multielement antennas which consist of interconnected, conductive structure elements of electrically small dimensions. The theory is based on the retarded electromagnetic potentials which permit a diakoptic approach to the problem. The antenna is broken up into its individual structure elements. Each element is assumed to be excited by currents which are impressed at its terminals, i.e., junctions with adjacent elements (current coupling) and by the electric fields of the currents and charges on all the other elements (fieid coupling). Both excitations are treated independently. Each impressed current produces a "dominant" current distribution, a characteristic of the element, which can be readily computed. Current coupling is formulated by "intrinsic" impedance matrices which relate the scaler potentials at the terminals of an element, caused by its dominant current distributions, to the impressed currents of the element. Field coupling produces "scatter" currents on all the elements and is formulated by a "fieid-coupling" matrix which relates the scalar potentials at the terminals, caused by field coupling, to the impressed currents at all the terminals. Intrinsic and "field-coupling" matrices are combined to form the "complete" impedance matrix of the diakopted antenna. Enforcing continuity of the currents and equality of the scalar potentials at all the interconnections between the elements yields a system of linear equations for the junction currents and the input impedance of the antenna. Current coupling dominates field coupling. Fieid coupling is primarily affected by the dominant current distributions of the elements, and in general the scatter currents have negligible effect on it. Although detailed numerical investigations will be presented in another paper, a simple example is included here to demonstrate that the diakoptic theory yields very good results even if greatly simplified assumptions are made.  相似文献   
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