Photooxidation by Pteridines'

Suinizary. A nunibl)er of pteridfines were examined( for activity in promotinig photop)hosphorylation in broken spinach chlioroplasts anid in stimlulating cvtochrome c photooxidation ill sonicated chloroplasts. Correlation was fouind between activities for the 2 reactions. Photophosphorylation promoted by pteridines was inhibited by DCMU and by anaerobic conditiolns. It is concluded that pteridines mlay stimulate photophosphorylatioIn by linkiinig photosystem 1 with molecular oxygen and thereby alloxving noncyclic electron flow. Aromatic pteridiiies in both the 2.4-dihidroxyan(d 2-amliuo-4-hydroxy-series were active; substitution at the 6 (or 7) position was a necessary but not sufficient condition for activity in b-oth reactions. Reducing agents incr-eased photophosphorylation activity of aromatic pteridines and an oxidant inicreased activity of a tetrahydropteridine. It is postulated that pteridines are imiost active in their seniiiquinone or uinstable (lihvdro fornms.