Synthesis of prenylquinones in chioropiasts

In recent studies evidence was obtained that chioropiasts of higher plants possess an autonotnic system of isoprenoid synthesis. The prenyl moiety of the chloroplast isoprenoid compounds [i,e, carotenoids, chlorophylls, plastoquinones, tocopherols and phylloquinone (vitamin K,)] originates frotn geranyigeranyi-PP, The present review deals with some aspects of the fonnatioo of the plastidic prenylquinones, i,e, a-tocopherol, plastoquinone-9 and phylloquinone, in which the isoprenoid synthesis as well as the shikimate pathway of aromatic compound synthesis are involved. This is illustrated by the scheme in Fig, 1 which is based on results of experiments predominantly carried out with spinach chioropiasts (see Soil and Schultz 1980, Schultz et al, 1981a, 1982), From early experiments in T, W, Goodwin's grotip on monocotyledons and dicotyledons it could be inferred that bicarbonate was incorporated into the abovementioned plastidic isoprenoid compounds, but not into cytoplastnatic compounds (e.g. sterols). This led to the stiggestion that a direct carbon flow exists from the Calvin cycle to mevalonate and polyprenyl compound synthesis (Goodwin 1965), This idea has been strongly supported by the results of recent studies on purified, intact chioropiasts as described in the following sections. Abbreviations (used in figures AdoMet, S-adenosylmethionine; Car, Carotene; CoA-SH, Coenzyme A; DAHP, 3-deoxyD-arabinoheptulosonate-7-phosphate; HMG-CoA, 3-liydroxy3-methylglutaryl-CoA; IPP, isopentenyl-PP; Me-6-PhQ (H^), 2-methyl-6-phytylquinone (quinol); PEP, phosphoenolpyruvate: PGA, 3-phosplio-D-giycerate; Phe, phenylalanine; PO-9, plastoquinone; ST, <5-tocopherol; <5TQ, 5-tocopheroIquinone; TLC, thinlayer chromatography; TPP, thiamine diphosphate.