Abstract
An enzyme termed nitrilase, which hydrolyzes nitriles to the corresponding carboxylic acids, is described. A method for its assay with indoleacetonitrile (IAN), separating quantitatively the resulting indoleacetic acid (IAA) is presented. The enzyme is not common in the plant kingdom, for of 29 plants (from 21 families) tested, 19 showed no activity and only members of the Gramineae (grasses), Cruciferae (cabbage group and radish), and Musaceae (banana family) were clearly active. Several fungi have the enzyme but do not excrete it into the culture medium. The enzyme has been partially purified from barley leaves. It is completely soluble, has optimum pH near 7, shows an energy of activation of 14,000 cals per mole, and a Michaelis constant for IAN of 5.1 × 10 −5 at 25 °C. It is susceptible to SH-reagents, and is slowly inactivated at 35 °C. and above in air. The conversion of IAN to IAA and ammonia is quantitative, requires no oxygen, and does not yield the free amide as an intermediate product. Electrophoresis on starch gel indicates that all activity is associated with a single protein fraction, so that the two stages of hydrolysis are probably carried out by one and the same enzyme.
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