Biosynthesis of ubiquinone in the rat.

Ruegg et al. (1959) and Linn et al. (1959) have reported that rat liver contains two ubiquinones with C46 and C50 side chains (coenzymes Q, and Qlo respectively), the former predominating. Experiments in this Laboratory confirmed the presence of both these ubiquinones in our stock-colony rats and also showed the presence of traces of ubiquinones with side chains containing 40 and 35 carbon atoms (Lawson, Mercer, Glover & Morton, 1960). Similar observations have also been made independently by others (Diplock, Edwin, Green, Bunyan & Marcinkiewicz, 1960). The occurrence of at least four ubiquinones in the rat raises the question of their origin. One or more may come from the diet, some components of which are known to contain ubiquinone (Page, Gale, Koniuszy & Folkers, 1959) and others may be formed by intestinal micro-organisms. The similarity between the ubiquinones and vitamins K2 suggests that the rat possibly makes use of a preformed substituted benzoquinone moiety, to which it may attach one of a series of polyisoprenoid units in a manner similar to that claimed by Martius & Esser (1958) for the utilization of 2methyl-1:4-naphthoquinone in the synthesis of vitamin K2 (with a polyisoprenoid side chain). It has already been shown that [2-14C]mevalonate (Gloor & Wiss, 1959a) and [1-L4C]acetate (Dialameh & Olson, 1959) can be incorporated in vivo into ubiquinone by the rat. The radioactivity was only in the side chain (Wiss, 1959; Gloor, Schindler & Wise, 1960) so the aromatic nucleusis presumably independently available. The origin of this substituted quinone portion of the molecule in the animal body is still unknown, although in micro-organisms similar quinones such