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

The weak signal obtained from the anomalous scattering (at λ = 1.54 Å) of naturally occurring elements such as sulfur, phosphorus and ordered solvent chloride ions is used to determine the atomic positions of these atoms. Two examples are discussed: the sulfur and chlorine substructure of tetragonal hen egg-white lysozyme and an oligonucleotide containing ten P atoms. The substructure of lysozyme was also solved from Cu Kα radiation data collected on a standard rotating-anode generator. The results presented here are an illustration of the power of the matrix methods, which are to be implemented in next distribution of the direct methods package CRUNCH.