DIURNAL COURSE OF QUERCETIN, RUTIN AND PHLORHIZIN EFFECT ON THE ACTIVITY OF THE BENSON-CALVIN CYCLE .1. GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASE COMPLEX

Quercetin, rutin and phloridzin inhibited the activity of glyceraldehy de-3-phosphate dehydrogenase (GPD) complex from spinach leaves. At a c oncentration of 5 x 10(-5) M they decreased the rate of 3-phosphoglyce rate (PGA) reduction by 90, 50-80 and 30-40 %, respectively. The activ ity of the effectors depended on the time of isolation of enzymes and the corresponding level of endogenic phenolic compounds. To estimate t he effect of the last factor, the enzyme preparation was obtained in t he presence and in the absence of insoluble polyvinylpyrrolidone (Poly clar AT). Using rutin it was shown that in the absence of endogenic ph enols the inhibition of PGA reduction was decreased as compared with t he variant without Polyclar AT. The effect of rutin was constant durin g the day. On the basis of data obtained the flavonoids are supposed t o inhibit the Benson-Calvin cycle at its reducing stage; this effect m ay be cooperative and depend on quantitative and qualitative content o f endogenic phenolic compounds.