Partial purification of nitrilase from Chinese cabbage

Nitrilase was purified ca 28-fold from Chinese cabbage seedlings. K_m values of 5.2 × 10^?4 and 2.6 × 10^?3 M were obtained for indoleacetonitrile (IAN) and 3-cyanopyridine (3-CP) as substrates. For hydrolysis of 3-CP, the maximal velocity was 44 times higher than for the natural substrate IAN. The pH optimum is at 7.5. IAA concentrations from 10^?6 to 10^?3 M did not inhibit the partially purified enzyme. Nitrilase activity was investigated during development of seedlings grown under continuous light. Roots with hypocotyls exhibited only slightly lower activity than cotyledons based on fresh weight, although their specific activity was ca 5 times higher. Etiolated seedlings showed a very similar distribution of nitrilase activity. The significance of the results for IAA biosynthesis is discussed.