| Summary: | Includes bibliographical references. === Nitrilases catalyse the conversion of a nitrile to its corresponding acid and ammonia by the addition of two water molecules. Cyanide dihydratases, a subgroup of nitrilases, specifically hydrolyse cyanide to formic acid and ammonia. Nitrilases are found in a diverse collection organisms that includes plants, bacteria and fungi. They form one branch a superfamily of structurally related enzymes that are believed to have in common a unique cys-glu-Iys catalytic triad. Many nitrilases exiat as a large molecular weight oligomers of more than 300kDa. In the current study the structures of two cyanide dihydratases, from Pseudomonas stutzeri AK61 and Bacillus pumilus Cl, have solved at a resolution 2.9nm and 32nm respectively by single particle reconstruction from electron micrographs of enzyme particles stained in uranyl acetate. Each enzyme consists of a spiral structure of well-defined length. It is proposed that this arrangement of subunits occurs in many other nitrilases and that a number of unexplained observations in the literature can reconciled by this model.
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