Characterisation of nitrilase and nitrile hydratase biocatalytic systems

Abstract

Bio-catalytic transformations converting aromatic and arylaliphatic nitriles into the analogous related amide or acid were investigated.These studies included synthesis of the beta-substituted nitrile 3-hydroxy-3-phenylpropionitrile, subsequent enrichment and isolation on this substrate of nitrite-degrading micro-organisms from the environment, and a comparative study of enzymatic reactions of nitriles by resting cell cultures and enzymes. Each biocatalyst exhibited a distinctive substrate selectivity profile, generally related to the length of the aliphatic chain of the arylaliphatic nitrile and the position of substituents on the aromatic ring or aliphatic chain. Cell-free nitrilases generally exhibited a narrower substrate range than resting whole cells of Rhodococcus strains. The Rhodococcus strains all exhibited nitrile hydratase activity and converted beta-hydroxy nitriles (but did not demonstrate enantioselectivity on this substrate). The biocatalysts also mediated the synthesis of a range of alpha-hydroxy carboxylic acids or amides from aldehydes in the presence of cyanide. The use of an amidase inhibitor permits halting the nitrile hydratase/amidase reaction at the amide intermediate.