45] Ubiquinone biosynthesis in plant mitochondria

Abstract

The biosynthesis of ubiquinones, starting from isopentenyl diphosphate and 4-hydroxybenzoate as natural precursors, requires several enzymatic steps such as prenyl transfer, 4-hydroxybenzoate, polyprenyl transfer, hydroxylation, decarboxylation, O-methylation, and methylation. In animal and yeast cells, these reactions occur within the mitochondria. It has been shown recently that plant mitochondria also perform several reactions in the biosynthesis of the ubiquinones. The biosynthesis of plant ubiquinones and the compartmentation of this pathway within the plant cell can be studied by incorporation of [1- 14 C]isopentenyl diphosphate, 4-hydroxy[carboxy- 14 C]benzoic acid, and S-[methyl- 14 C]-adenosylmethionine into ubiquinone intermediates by isolated mitochondria from potato tubers ( Solanum tuberosum ). For the identification of the ubiquinone intermediates, three criterias are used as follows: (1) cochromatography with standards, (2) incorporation of radioactivity from the different substrates and radioactivity ratios, and (3) chemical modification followed by rechromatography (acetylation using acetic anhydride, silylation using chlorotrimethylsilan, reduction using NaBH 4 ).