A note on the enzymic action and biosynthesis of a nitrile‐hydratase from a Brevibacterium sp.

The effect of different compounds on the enzymic action of the nitrile‐hydratase used for the bioconversion of nitriles was studied. An excess of acrylonitrile as a substrate was shown to inhibit the activity of the enzyme. This inhibition occurred only at relatively high substrate concentrations (0.2 mol/l or more). The nitrile bioconversion products (acrylamide, propionamide) and their structural analogues (acrylic acid, thioacetamide) were shown to inhibit the enzyme competitively. The most important inhibition found was that of cyanide (K i = 0.004 mol/l), a break down product of some nitriles. By using an acetamidase‐negative mutant, amides were shown to inhibit biosynthesis of nitrile‐hydratase. An identical result was obtained with thioacetamide, a non‐substrate compound for acetamidase. This compound repressed the biosynthesis of nitrile‐hydratase by both the wild type and the acetamidase‐negative mutant to the same extent.