INTRACELLULAR-LOCALIZATION OF P-HYDROXYBENZOATE GERANYL-TRANSFERASE, A KEY ENZYME INVOLVED IN SHIKONIN BIOSYNTHESIS

The intracellular localization of p-hydroxybenzoate geranyltransferase , a key enzyme involved in shikonin biosynthesis in Lithospermum cell cultures was investigated. Fractionation of the microsomal components by continuous sucrose density gradient centrifugation showed that the enzyme was localized in a membrane fraction with a density of rho = 1. 09-1.10 g cm-3, which was distinctly different from those of the plast id and plasma membranes and tonoplast but was similar to that of the e ndoplasmic reticulum. Electron microscopic examination of the fraction having the p-hydroxybenzoate geranyltransferase activity revealed the presence of numerous vesicles (0.1-0.5 mum in diameter) which probabl y correspond to the secretion vesicles that are known to be derived fr om rough ER and responsible for excreting shikonin from the cells.