Abstract
In the first part, nine crystal structures of imidazole compounds have been determined by X-ray crystallography. Their coordination geometry and crystal packing are described. This part of work helped the author to be accustomed to crystallography. In the second part, the structure of agglutinin from Abrus precatorius has been determined by X-ray crystallography. The structure and the activity as a ribosome-inactivating protein (RIP) have been compared with abrin-a from Abrus precatorius. With docking study, ASN200 of abrin-a was found to be hydrogen bonded with G4323 of 28SRNA, while corresponding PRO199 of agglutinin is a non-polar residue. This may explain the lower toxicity of agglutinin than abrin-a, despite of similarity in secondary structure and the activity cleft of two RIPs.