The use of phase combination in the refinement of phosphoglycerate kinase at 2.5 A resolution

The combination of phase information obtained by the method of isomorphous replacement with that calculated from a partial model of the structure has proved to be a powerful tool in the interpretation of the structure of horse muscle phosphoglycerate kinase. That the combined phases are an improvement on the calculated or isomorphous ones is evidenced by more readily interpretable electron density maps, which show only a low level of feedback from incorrectly located atoms. Several different types of Fourier syntheses have been calculated using the combined phase angles and an essentially qualitative evaluation of their relative merits is presented.