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 plastid and plasma membranes and tonoplast but was similar to that of the endoplasmic 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 probably correspond to the secretion vesicles that are known to be derived from rough ER and responsible for excreting shikonin from the cells.