Abstract
The localization of ubiquinone (UQ) and plastoquinone (PQ) biosynthesis in subfractions isolated from spinach leaves has been studied. UQ-9 and UQ-10 were found mainly in mitochondria, whereas PQ was enriched in chloroplasts, but also found in Golgi membranes. alpha-Unsaturated polyprenol-11 was also present at a low concentration in chloroplasts. Autoradiography revealed the presence of nonaprenyl-4-hydroxybenzoate (NPHB) and nonaprenyl-2-methylquinol (NPMQ) transferase activities involved in quinone biosynthesis in all subfractions, but the specific activities involved in quinone biosynthesis in the total microsomal fraction were 20 times higher than those in mitochondria and chloroplasts. The isolated Golgi vesicles were particularly enriched in both activities. When the incubation medium containing total microsomes or Golgi membranes was supplemented with NADH, NADPH, S-adenosylmethionine, and an ATP-generating system, NPHB and NPMQ were transferred to UQ-9 and PQ, respectively. trans-Prenyltransferase, which synthesizes the side chain of UQ and PQ, was present in the total microsomal fraction. With farnesyl-PP as substrate, no product was formed, but with geranyl-PP, solanesyl-PP was synthesized and transferred to 4-hydroxybenzoate present in the total microsomal fraction. The results show that these membranes from spinach contain farnesyl-PP synthetase. It is concluded that the plant leaf Golgi membranes contain the enzymes for both UQ and PQ biosynthesis and that a specific transport and targeting system is required for selective transfer of UQ to the mitochondria and of PQ to the chloroplast.
Highlights
From the $Departmentof Biochemistry, Arrhenius Laboratories for Natural Sciences, University of Stockholm, S-106 91 Stockholm, and the TClinical Research Center at Huddinge Hospital, Karolinska Institutet, S-14186 Huddinge, Sweden
The localization of ubiquinone (UQ) and plastoqui- and followed by the condensation reactionscatalyzed by the none (PQ) biosynthesis in subfractions isolated from spinach leaves habseen studied
UQ-9 and UQ-10 were found mainly in mitochondria, whereas PQ was enriched in chloroplasts, and found in Golgi memtrans-prenyltransferase [2, 3]
Summary
NADPH, S-adenosylmethionine,and an ATP-generating system, NPHBand NPMQ were transferred tUoQ-. Polyisoprenoid synthesis occurs in all plant cells, giving rise to a large number of isoprenoid products. This pathway is responsiblefor supplying major products such as monoand diterpenes, chlorophyll, tocopherol, carotenoids, and sapthat this organelle was a site for UQ biosynthesis [13]. Are produced via this pathway,which involves a number In thecase of UQ recent investigations on mammaliacnells of enzymatic steps, initially converting acetyl-coA to FPP’ have led to the conclusion that this lipid is present in mitochondria but in most biological membranes where it. The results indicate thata complex mechanism of lipid biosynthesis, redistribution, and sorting in these cells requires the interaction of several membrane systems
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