Stimulation of photophosphorylation and cytochrome c photooxidation by pteridines.
A number of pteridines were examined for activity in promoting photophosphorylation in broken spinach chloroplasts and in stimulating cytochrome c photooxidation in sonicated chloroplasts. Correlation was found between activities for the 2 reactions. Photophosphorylation promoted by pteridines was inhibited by DCMU and by anaerobic conditions. It is concluded that pteridines may stimulate photophosphorylation by linking photosystem 1 with molecular oxygen and thereby allowing noncyclic electron flow. Aromatic pteridines in both the 2,4-dihidroxy- and 2-amino-4-hydroxy-series were active; substitution at the 6 (or 7) position was a necessary but not sufficient condition for activity in both reactions. Reducing agents increased photophosphorylation activity of aromatic pteridines and an oxidant increased activity of a tetrahydropteridine. It is postulated that pteridines are most active in their semiquinone or unstable dihydro forms.
D002736:Chloroplasts; D003580:Cytochromes; D066298:In Vitro Techniques; D010788:Photosynthesis; D011621:Pteridines
D003580:Cytochromes; D011621:Pteridines