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K M Andersson

Publications and source records attributed to K M Andersson.

4 recordsLinked to original sources
PubMed2000

The protein content in crystals and packing coefficients in different space groups.

A precise way of estimating the packing coefficient, i.e. the ratio between the protein and unit-cell volume, or solvent content in protein crystals is given. At present, the solvent content is not given for most proteins in the Protein Data Bank and in many cases where it is given the values are dubious. The mean density of proteins in the crystalline form is around 1.22 g cm(-3), not 1.35 g cm(-3) as usually stated. This is equivalent to 19.5 A(3) per non-H atom. A statistical investigation of the average protein content and packing coefficient in different space groups is presented. The packing coefficients are generally higher in the most frequently occurring space groups than in the uncommon space groups. There is also a remarkable difference in frequency distribution for enantiomorphous pairs of space groups.

Crystallization↗
PubMed1996

Phasing proteins at low resolution.

A method for obtaining phases of low-order reflections is presented. It is based on four observations: (1) the electron density inside proteins is smooth and uniform at low resolution. (2) Since all proteins have almost the same density, the total volume of the protein is known if the molecular weight is known. (3) The overall shape of many proteins is fairly spherical. (4) The total scattering from a sphere of uniform density is in phase with a point scatterer at its centre of gravity, up to a well defined cross-over. After the first cross-over the total protein molecule scatters out of phase with its centre. If the centre of the protein can be found, the phases of typically the ten lowest resolution reflections can be very accurately determined. The method works, provided low-order reflections can be measured accurately and the centre of gravity can be well positioned from these data. The correctly phased low-resolution reflections may be used as a starting set for phase extension. By combining the measured amplitudes with these phases we believe that the size and low-resolution shape of an unknown protein, i.e. the envelope of the molecule, can be obtained.

Journal Article↗
PubMed1986

Conceptual problems in primary health care research.

Concepts are basic elements in all scientific work. New fields of investigation, like primary health care, have to adopt new concepts. These may have a, more or less, physical appearance or may be phenomenological by nature. Concepts may be defined by description or, more appropriate, by explication of necessary and sufficient attributes or characteristics, or by criteria to be fulfilled. One model for concept analysis contains steps as: determine the aims of analysis, identify all uses of the concept, determine the defining attributes, construct a model case, and define empirical referents. Another model, developed for analysis of phenomenological concepts, is based on accumulation of hundreds of explications of the meaning of the concept. Those are elaborated by Grouping, Reduction, Elimination, Hypothetical identification, Application, Final identification. Methods for concept analysis need to be further emphasized in doctoral programs. Even experienced scientists may need more training in such methods, when entering new fields. Students need accurate guidance through passages of conceptual work. Concept development should be accepted and encouraged as research projects in its own capacity. It makes quite a contribution to scientific knowledge, to elaborate an important concept in all aspects. In addressing new empirical problems, much work should be spared, if the researcher could use concepts already studied and described in the literature.

Concept Formation↗