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computer programs
The restrained reciprocal-space least-squares refinement program of Hendrickson & Konnert [Computing in Crystallography, edited by R. Diamond, S. Ramaseshan & K. Venkatesan, pp. 13.01–13.25. (1980). Bangalore: Indian Academy of Sciences] has been modified to include non-bonded and/or hydrogen-bonded contacts between molecules related by symmetry operations and/or unit-cell translations. The modified program has been tested on an inhibited form of aspartate aminotransferase, which is an α2 dimeric enzyme with a crystallographic twofold axis relating the subunits. A number of heretofore unseen close contacts between atoms of separate subunits were located and correctly dealt with by the modified program.