Matrix methods for solving protein substructures of chlorine and sulfur from anomalous data

The weak signal obtained from the anomalous scattering (at lambda = 1.54 An gstrom) of naturally occurring elements such as sulfur, phosphorus and orde red solvent chloride ions is used to determine the atomic positions of thes e atoms. Two examples are discussed: the sulfur and chlorine substructure o f tetragonal hen egg-white lysozyme and an oligonucleotide containing ten P atoms. The substructure of lysozyme was also solved from Cu K alpha radiat ion data collected on a standard rotating-anode generator. The results pres ented here are an illustration of the power of the matrix methods, which ar e to be implemented in next distribution of the direct methods package CRUN CH.