Subcellular localization of rice leaf aryl acylamidase activity

The intracellular localization of aryl acylamidase (aryl-acylamide amidohydrolase, EC 3.5.1.13) in rice (Oryza sativa L. var Starbonnet) leaves was investigated. The enzyme hydrolyzes and detoxifies the herbicide propanil (3,4-dichloropropionanilide) thereby accounting for immunity of the rice plant to herbicidal action. Fractionation of mesophyll protoplasts by differential centrifugation yielded the highest specific activity of amidase in the crude mitochondrial fraction. Further separation of density gradients of the silica sol Percoll also indicated that this enzyme was mitochondrial. By the use of biochemical markers, the purified mitochondrial fraction was shown to be substantially free of contamination from nuclei, chloroplasts, golgi, and plasma membranes. Subfractionation of the purified mitochondria suggests that this enzyme is located on the outer membrane.