Subcellular localization of 3-hydroxy-3-methylglutaryl coenzyme A reductase and other membrane-bound enzymes in sweet potato roots1

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Abstract
The subcellular localization of 3-hydroxy-3-methylglutaryl coenzyme A reductase and other membrane-bound enzymes in fresh, cut and diseased sweet potato root tissues was resolved by differential centrifugation and sucrose density gradient centrifugation. In fresh, cut and diseased tissues, cytochrome c oxidase was almost localized in mitochondria, and NADH cytochrome c reductase was in mitochondria in fresh and cut tissues, but in both mitochondria and microsomes in diseased tissue. NADPH cytochrome c reductase and antimycin A insensitive NADH cytochrome c reductase were mainly associated with microsomes. Catalase was dominantly found in the mitochondrial fraction. 3-Hydroxy-3-methylglutaryl coenzyme A reductase was localized only in mitochondria and not in microsomal and supernatant fractions in both fresh and cut tissues. In diseased tissue (infected with Ceratocystis fimbriata), in addition to being present in mitochondria, the enzyme was also localized in microsomes. These results indicate that microsomal 3-hydroxy-3-methylglutaryl coenzyme A reductase whose activity rapidly increased in response to the infection, predominandy participates in the formation of terpenes such as ipomeamarone.