Nitrilases branches

Cyanide hydratase and cyanide dihydratase belongs to the nitrilase branch of nitrilase superfamily, using HCN as the only efficient substrate and producing amide and acid products, respectively. Microorganisms appear in fact to have evolved separate metabolic pathways for the hydrolysis of inorganic cyanide. Thus, most nitrilases (as well as nitrile hydratases) till now investigated do not display activity... 

Among aliphatic nitriles, unbranched saturatured or unsaturated compounds with a medium chain length (for instance, propionitrile, butyronitrile, hexaneni-trile, and acrylonitrile) are hydrolyzed with the highest relative rate (about 20-35% of that for benzonitrile) by aromatic nitrilases. Branched nitriles are in general poor substrates of these enzymes but, for instance, isobutyronitrile is one of the best substrates of the aliphatic nitrilase from R. rhodochrous K22 [28]. 

Branches of Nitrilase Superfamily with Their Substrates... 

Nitrilases are classified into branch 1 of the nitrilase superfamily, which is comprised of enzymes acting on various nonpeptide CN bonds [15]. All the proteins of this superfamily are characterized by a conserved catalytic triade (glu, lys, cys) and an additional conserved glu residue that seems to participate in the reaction mechanism [2]. Members of class 1 transform the CN bonds in nitriles and cyanides. The enzymes in which these activities were confirmed share in some cases levels of aa sequence identity as low as about 20%. This sequence diversity is reflected in different substrate specificities and different reaction products (carboxylic acids, amides) in various subtypes of these enzymes (aromatic nitrilases, aliphatic nitrilases, arylacetonitrilases, cyanide hydratases, cyanide dihydratases). 

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