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

Abstract

Free purines at concentrations of around 10-4 M stimulate the endogenous respiration of washed, nitrogen starved cells of C. vulgaris up to 3-fold. This stimulation is not due to the oxidation of the purines themselves, nor to the liberation of inorganic nitrogen compounds. Structure activity studies using close to 100 purines and purine analogues indicate that a bicyclic, fully aromatic ring system with at least 2 N atoms in each ring appears to be necessary for activity. The size of the substituents at the 6 position of the purine ring must be smaller than 5 A in order to retain activity. Substitution at other positions on the rings tends to decrease activity. Large inhibitions of the activities of active compounds were observed when inactive compounds were added to the incubation mixtures, suggesting a 2-point attachment theory for the mode of action of these compounds.