Replacement method

Rules for the design of shells of revolution under internal pressure differ from the Division 1 rules, particularly the rules for formed heads when plastic deformation in the knuckle area is the failure criterion. Shells of revolution for external pressure are determined on the same criterion, including safety factors, as in Division 1. Reinforcement for openings uses the same area-replacement method as Division 1 however, in many cases the reinforcement metal must be closer to the opening centerline. 

Such structures are most simply named by the replacement method, using the ending -onia instead of -a in the replacement prefixes. In the examples, such names are compared with A-ylium names, which are derived quite differently. 

Srratification is a desirable strategy to provide efficient room air condi-noning with much less effort than using the piston strategy. Its mam application in room air conditioning is the thermal replacement method. However, it can also be applied for contaminants without any thermal buoyancy sources that have different density from the room air. Examples of different air distribution methods to create thetma teplacement are presented in Fig. 8.12. 

The isomorphous replacement method requires attachment of heavy atoms to protein molecules in the crystal. In this method, atoms of high atomic number are... 

The molecular replacement method assumes similarity of the unknown structure to a known one. This is the most rapid method but requires the availability of a homologous protein s structure. The method relies on the observation that proteins which are similar in their amino acid sequence (homologous) will have very similar folding of their polypeptide chains. This method also relies on the use of Patterson functions. As the number of protein structure determinations increases rapidly, the molecular replacement method becomes extremely useful for determining protein phase angles. 

Fig. 8.11 Illustration of the basic steps followed by the Molecular Fragment Replacement method to build a model of the structure of the protein Dinl.

The TER assay of rat skin is a fully accepted replacement method of animal tests for skin corrosion. Hence, in the EU the TER assay is mandatory for the evaluation of test substances. Investigation of animals to test the corrosivity of chemicals and/or other substances is not permitted [151],... 

The human skin model assay can provide further data on the degree of corrosiveness and allows ranking corrosives among each other. It is, therefore, accepted as a replacement method of animal tests for skin corrosion in the EU. 

The isomorphous replacement method requires attachment of heavy atoms to protein molecules in the crystal. In this method, atoms of high atomic number are attached to the protein, and the coordinates of these heavy atoms in the unit cell are determined. The X-ray diffraction pattern of both the native protein and its heavy atom derivative(s) are determined. Application of the so-called Patterson function determines the heavy atom coordinates. Following the refinement of heavy atom parameters, the calculation of protein phase angles proceeds. In the final step the electron density of the protein is calculated. 

Rossmann, M.G. The Molecular Replacement Method. Gordon Breach, New York, 1972. 

Chemical Recovery Cartridge Metallic Replacement Method... 

Deamination replaces the amine group with a hydrogen atom. This process normally uses hypophosphorous acid, H3PO2. The general process for deamination is in Figure 13-32. This is a synthetically useful technique that leads to different products than other replacement methods. Figure 13-33 illustrates the formation of two different dibromotoluenes. 

Green, D. W., Ingram, V. M. and Perutz, M. F. (1954). The structure determination of heamoglobin IV. Sign determination by the isomorphous replacement method. Proc. R. Soc. London A225, 287-307. 

The integrated molecular replacement method comparison of automatic protocols... 

Crowther, R. A. (1972). The fast rotation function. In The Molecular Replacement Method, Rossmann, M. G., ed. Gordon and Breach, New York, pp. 173-185. 

Rossmann, M. G. (1990) The molecular replacement method. Acta Crystallogr. A 46, 73-82. 

Ramakrishnan, V. and Biou, V. (1997). Treatment of multiwavelength anomalous diffraction data as a special case of multiple isomorphous replacement. Method Enzymol. 276, 538-557. 

Rayment, I. (1983). Molecular replacement method at low resolution optimum strategy and intrinsic limitations as determined by calculations on icosahedral virus models. Acta Crystallogr. A 39,102-116. 

Openings are always required in pressure-vessel shells and heads. Stress intensification is created by the existence of a hole in an otherwise symmetrical section. The code compensates for this by an area-replacement method. It takes a cross section through the opening, and it measures the area of the metal of the required shell that is removed and replaces it in the cross section by additional material (shell wall, nozzle wall, reinforcing plate, or weld) within certain distances of the opening centerline. These rules and formulas for calculation are included in Subsec. A. 

In order to understand the interactions between these bis-intercalating drugs and IMA more fully, we have crystallized several complexes of them and undertaken the structure determination by x-ray diffraction technique. One of the crystal forms diffracts to 1.6 A resolution with a space group of F222. The crystal structure was determined by the multiple isomorphous replacement method using three different heavy atom derivatives. The structure was refined to an R-factor of 19% and there were moderate number of solvent molecules clearly visible. The crystal... 

Table I lists isomorphous replacements for various metalloproteins. Consider zinc enzymes, most of which contain the metal ion firmly bound. The diamagnetic, colorless zinc atom contributes very little to those physical properties that can be used to study the enzymes. Thus it has become conventional to replace this metal by a different metal that has the required physical properties (see below) and as far as is possible maintains the same activity. Although this aim may be achieved to a high degree of approximation [e.g., replacement of zinc by cobalt(II)], no such replacement is ever exact. This stresses the extreme degree of biological specificity. The action of an enzyme depends precisely on the exact metal it uses, stressing again the peculiarity of biological action associated with the idiosyncratic nature of active sites. (The entatic state of the metal ion is an essential part of this peculiarity.) Despite this specificity, the replacement method has provided a wealth of information about proteins that could not have been obtained by other methods. Clearly, there will often be a compromise in the choice of replacement. Even isomorphous replacement that should retain structure will not necessarily retain activity at all. However, it has become clear that substitutions can be made for structural studies where the substituted protein is inactive (e.g., in the copper proteins and the iron-sulfur proteins). It is also possible to substitute into metal coenzymes. Many studies have been reported of the...

These two compounds were solved together, using an isomorphous replacement method [6]. Fig. 6 shows the c-axis projection of theophylline. Caffeine has the hydrogen in the intermolecular hydrogen... 

In 1954, Perutz introduced the isomorphous replacement method for determining phases. In this procedure a heavy metal, such as mercury or platinum, is introduced at one or more locations in the protein molecule. A favorite procedure is to use mercury derivatives that combine with SH groups. The resulting heavy metal-containing crystals must be isomorphous with the native, i.e., the molecules must be packed the same and the dimensions of the crystal lattice must be the same. However, the presence of the heavy metal alters the intensities of the spots in the diffraction pattern and from these changes in intensity the phases can be determined. Besides the solution to the phase problem, another development that was absolutely essential was the construction of large and fast computers. It would have been impossible for Perutz to determine the structure of hemoglobin in 1937, even if he had already known how to use heavy metals to determine phases. 

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