ABSTRACT: 1. Twenty-two aerobically grown Gram-negative bacteria were analysed for demethylmenaquinones, menaquinones, 2-polyprenylphenols, 6-methoxy-2-polyprenylphenols and ubiquinones. 2. All the eight enterobacteria and both the two facultative organisms (Aeromonas punctata and Aeromonas hydrophila) examined contain all the compounds listed above. The principal homologues are octaprenyl; in addition lower (down to tri- or tetra-prenyl for the 2-polyprenylphenols) and sometimes higher homologues are also present. 3. Strict aerobes are of two types, those that contain 2-polyprenylphenols, 6-methoxy-2-polyprenylphenols and ubiquinones, and those that contain ubiquinones only. The principal homologues are generally octa- or nona-prenyl, although one organism (Agrobacterium tumefaciens) has ubiquinone-10 as its principal homologue. As in the enterobacteria, lower homologues of these compounds are also present. 4. In Escherichia coli W, Pseudomonas ovalis Chester and Pseudomonas fluorescens, radioactivity from p-hydroxy[U-(14)C]benzoic acid is incorporated into 2-polyprenylphenols, 6-methoxy-2-polyprenylphenols, 6-methoxy-3-methyl-2-polyprenyl-1,4-benzoquinones, ubiquinones and a compound tentatively identified as 2-polyprenyl-1,4-benzoquinone. The fact that radioactivity is incorporated into the first three compounds suggests that in these organisms, and indeed in all those Gram-negative bacteria that contain 2-polyprenylphenols and 6-methoxy-2-polyprenylphenols, ubiquinones are formed by a biosynthetic sequence similar to that in Rhodospirillum rubrum. 5. The finding in ;Vibrio O1' (Moraxella sp.) and organism PC4 that 2-polyprenylphenols and 6-methoxy-2-polyprenylphenols are chemically and radiochemically undetectable leads to the conclusion that they are not intermediates in the biosynthesis of ubiquinone by these and by other Gram-negative bacteria that do not contain detectable amounts of 2-polyprenylphenols and 6-methoxy-2-polyprenylphenols. However, ;Vibrio O1' (organism PC4 was not examined) does contain 6-methoxy-3-methyl-2-polyprenyl-1,4-benzoquinone. 6. In Ps. ovalis Chester, radioactivity from l-[Me-(14)C]methionine is incorporated into the nuclear C-methyl and O-methyl groups of 6-methoxy-3-methyl-2-polyprenyl-1,4-benzoquinones and ubiquinone-9, and into the O-methyl group of 6-methoxy-2-polyprenylphenols.
