Observations on the Biosynthesis of Ubiquinones by Animals

Abstract

1. Tissues of a number of avian and mammalian species have been examined for the presence of 2-polyprenylphenols7 6-methoxy-2-polyprenylphenols, 6-methoxy-2-polyprenyl-1,4-benzoquinones and 5-demethoxyubiquinones. I n no instance was evidence found of the presence of any of these compounds, although most tissues contained a t least two ubiquinones and one ubiquinol.2. Tracer studies with g~-hydroxy[U-~~C]benzoic acid have been carried out to detect the precursor of ubiquinone-9, "5-demethoxyubiquinone-9", reported by Olson and co-workers [14,15] in rat liver. The results obtained provided good evidence that this compound is ubiquinol-9.As in the cases of gram-negative bacteria, green algae, higher plants, moulds, protozoa and yeasts [l--81, p-hydroxybenzoic acid has been shown to be a most effective precursor of ubiquinones in higher animals (monkey, mouse and rat) [3,4,9,10]. The intermediates involved in the conversion of this acid to ubiquinones by higher animals have still to be defined, although there would appear to be some evidence that they are the same as those which participate in the biosynthesis of ubiquinones by photosynthetic and some non-photosynthetic gramnegative bacteria (Scheme 1) [ll-131. Thus, Olson COzHCOz H I Iand co-workers have isolated a precursor of ubiquinone-9 from rat liver which they have suggested is 5-demethoxyubiquinone-9 (V, n = 9) [14,15]. I n addition, these workers have presented some evidence for the presence in rat liver of 6-methoxy-2-nonaprenylphenol (111, n = 9)

Intermediates of tocopherol biosynthesis in the unicellular alga Scenedesmus obliquus. The presence of three isomeric methylphytylbenzoquinones

“…A quinone with the properties of a hydroxylated phylloquinone was also found in S. obliquus. 5'-Hydroxyphylloquinone has been identified in Euglena gracilis strain Z (Law et al, 1973) and a similar, and possibly identical, compound has been found in Anacystis nidulans and Chlorella pyrenoidosa (Henninger et al, 1965;Allen et al, 1967;Whistance & Threlfall, 1970b). The compound found in S. obliquus had chromatographic properties similar to those quoted by Law et al (1973), a u.v.…”

Pathway for Ubiquinone Biosynthesis in Escherichia coli K-12: Gene-Enzyme Relationships and Intermediates

“…This method relies on the steady-state level of an intermediate being sufficiently high to allow its isolation and identification. Unfortunately, few intermediates in a pathway may be present in such quantities, and in some cases none of the intermediates may be detectable (17,26,28,29). Nevertheless, a number of polyprenylphe- The reactions affected by mutations in the various ubi genes are also shown.…”

4-Hydroxyphenylpyruvate dioxygenase is bound to thylakoid membranes from the cyanobacteriumAnacystis nidulans

“…The size of the plastoquinone pool is large compared to that of the other electron carriers [1]. Homogentisic acid (2,5-dihydroxyphenylacetic acid) is the precursor for the aromatic moiety of the plastoquinone molecule from higher plants and from Anacystis nidulans, a cyanobacterium [2]. 4-Hydroxyphenylpyruvate dioxygenase [EC 1.…”