Isolation and some properties of an aryl acylamidase from red rice, Oryza sativa L., that metabolizes 3',4'-dichloropropionanilide

An aryl acylamidase (aryl-acylamine amidohydrolase, E. C. 3.5.1.a)was isolated from red rice (Oryza sativa L.) seedlings and purifiedapproximately 5-fold with ammonium sulfate precipitation andgel filtration. The enzyme hydrolyzed 3',4'-dichloro- propionanilide(propanil) and several other mono- and dichloro-substitutedpropionanilides and 3',4'-dichloroanilide alkyl analogs. Substratespecificity tests on these analogs indicated the following substratepreference: propanil > 3'-chloropropionanilide > propionanilide> 4'-chloropropionanilide 3',5'-dichloropropionanilide 2'- chioropropionanilide. Tests on a series of 3',4'-dichloroanilidealkyl analogs of propanil revealed: propanil > 3,4-dichloroacetanilide> 3',4'-dichlorovaleranilide. The apparent Km for 3',4'-dichloropropionanilide was determinedfrom a double reciprocal plot of initial velocities at severalsubstrate concentrations. A value of Km=2.5 ? 10^–5 M wasobtained. The temperature optimum, when assayed with propanilas substrate, was 50?C. Although the pH optimum was 8.2, therewas relatively high enzyme activity over a wide range of pHvalues between 7.4–8.7. Several compounds, e.g. p-benzoquinone,pyrocatechol and CuSO₄, were found to effectively inhibit theenzyme activity on propanil. These results indicated that theproperties of this aryl acylamidase from red rice are very similarto those of enzymes from a commercial rice variety and fromother plant species. ¹ Mississippi Agricultural and Forestry Experiment Station cooperating. (Received January 6, 1978; )