Synthesis of 3-polyprenyltoluquinols and 4-carboxy-2-polyprenylphenols by cell-free preparations of Euglena gracilis

Cell-free homogenates of Euglena gracilis are able to carry out the light- and Mg²⁺-independent syntheses of approximately equal amounts of a nonaprenyltoluquinol, an octaprenyltoluquinol and two uncharacterized compounds referred to as chromanols from homogentisate and a Micrococcus luteus extract that has been preincubated with isopentenylpyrophosphate (MLE-IPP). In addition they also synthesized substantial amounts (20%) of previously unencountered CHCl₃-soluble products from homogentisate and MLE-IPP, and the 2-deca-, 2-nona- (principal product) and 2-octa-prenyl forms of 4-carboxy-2-polyprenylphenol from p-hydroxybenzoate and MLE-IPP. The polyprenyltoluquinols were shown to be 3-polyprenyl-toluquinols, compounds postulated as intermediates on the pathway from homogentisate to plastoquinone, by determination of the ratio of ¹⁴C: ³H incorporated into them from 2,5-dihydroxyphenylacetic-U-¹⁴C,4,6-³H₂] acid. Intracellular distribution studies using green, dark-grown and streptomycin-bleached cells, established that the 3-polyprenyltoluquinols are synthesized in the chloroplasts and the etioplasts, and that 4-carboxy-2-polyprenylphenols are synthesized in the mitochondria and a particle sedimenting at 1000–15000 g.