Stimulation of the Respiration of Chlorella Vulgaris by Purines and Purine Analogues.

[In the course of studies of the inicorporation of adenine-8-C14 into the nucleic acids of Chlorella vtilgaris we observed an unexpectedly large formation of C'402 by the cultures in the dark. \When the oxidation of adenine in this system wvas followed manometrically, it was found that Up to 10 or 20 times more oxygen was taken up by the cells than could be accounted for by assuming the conmplete oxidation of the adenine to CO), ammonia an(d water. The list of compounds which have been reported to stimulate the respiration of Chlorella is long, but the compounds have generally been either metabolic inhibitors such as HCN (17), 2,4-dinitrophenol (13), or p-chlorophenyl-1,1-dimethylurea (5), or simple nitrogenous compounds acting on nitrogen starved cells (10, 12). The compounds of the first group are not typical constituents of living systems, and beyond the observation that some or all of them uncouple oxidative phosphorylation, little is known about their mode of action. The stimiiulation of respiration causedl by inorganic nitrogen compounds has been investigated thoroughly and it is believed (11) that it is due to the increased axvailability of acceptors for oxidative phosphorylation via the formation of glutamine andl adenosine cliphosphate from glutamic acid, ammonia and adeniosine triphosphate. Quite in line with this hypothesis, Hattori (6) found that the oxygen uptake caused by the addition of inorganic nitrogen compounds was only of the or(ler of 1 or 2 T\J per mole atom of nitrogen added. By contrast to these findings, it is shown in this paper that the stimulation of respiration which is causecl by the purines is at least 10 times greater than that observed for inorganic nitrogen compounds, and must involve an entirely different mode of action. Because these stimulations occurred with natural substances as well as with their synthetic analogues it was of initerest to investigate the structural requirements for activity. The results of these studies are reportedl below.