Some additional features of one-wavelength anomalous dispersion.

Abstract

By use of appropriate algebraic formulas, illustrations are given of several characteristics of one-wavelength anomalous-dispersion data, for the case that one predominant type of anomalous-scattering atom is present. It is shown that, when the structure of the anomalous scatterer is known, some simple algebraic formulas may be used to generate initial values of many phases associated with a macromolecular structure. In some cases, there may be enough phases determined to permit further refinement and extension by use of current techniques for doing so. Another calculation shows the virtue of including isomorphous-replacement data and how readily that is done in an algebraic system. It is also shown that there is an advantage in accuracy through the use of a particular statistical calculation of the magnitude of the structure factors for the anomalous scatters, even when the magnitudes are known accurately because the structure of the anomalous scatterers is known. This occurs because the statistical values are scaled to adjust to errors in the data and thus avoids a disparity in scale that would occur otherwise in the algebraic system. With highly accurate data, the advantage would disappear. It is also shown, however, that, even with accurate one-wavelength anomalous-dispersion data, the coupling of isomerophous-replacement data leads to greater accuracy in evaluating phase differences than coupling with known magnitudes for the structure factors associated with the anomalous scatterers.(ABSTRACT TRUNCATED AT 250 WORDS)