Inhibition of Photophosphorylation by Kaempferol

Abstract

Kaempferol, a naturally occurring flavonol, inhibited coupled electron transport and both cyclic and noncyclic photophosphorylation in isolated pea (Pisum sativum) chloroplasts. Over a concentration range which gave marked inhibition of ATP synthesis, there was no effect on There have been no reports describing the effects of flavonoids on the reactions of chloroplasts, either in vivo or in vitro. Since kaempferol is a common naturally occurring flavonoid (3, 5), we have studied its effects on reactions of isolated pea chloroplasts. We will demonstrate that kaempferol is a potent inhibitor of photophosphorylation at concentrations which are physiologically significant. MATERIALS AND METHODSChloroplasts were isolated from 10-to 14-day-old pea leaves, Pisum sativum var. Alaska. Ten grams of leaf and stem tissue were homogenized for 5 sec in a Waring Microblender in 20 ml of grinding solution (0.4 M sorbitol; 0.1 M Na-Tricine, pH 7.8; 0.07 M sodium ascorbate; and 2 mg/ml of bovine serum albumin). The brei was filtered through 4 and then 12 layers of cheesecloth and centrifuged at lOOOg for 10 min. The resulting chloroplast pellet was dispersed in 1 ml of resuspension mix (0.4 M sorbitol; 0.05 M Na-Tricine, pH 7.8; 0.01 M KCI; and bovine serum albumin, 5 mg/ml). Chl concentration was determined according to Arnon (1).

Damage and protection of the photosynthetic apparatus from UV-B radiation. II. Effect of quercetin at different pH

“…Previous studies have shown that quercetin interacts with both the ATP complex (CF 1 factor) and the components of the electron-transport pathway (Q B -protein complex) in spinach thylakoid membranes (Moreland and Novitzki, 1987). Some authors established that quercetin inhibits the electron transport (Moreland and Novitzki, 1987), while others claimed that it is unaffected (Arntzen et al, 1974). Takahama (1983) suggested that quercetin can serve as an antioxidant in chloroplasts and suppresses lipid photoperoxidation as the effects depend on the flavonol concentration.…”

Effect of encecalin, euparin and demethylencecalin on thylakoid electron transport and photophosphorylation in isolated spinach chloroplasts

“…It is well known that some secondary metabolites such as phlorizin (Izawa et al 1966), kaempferol (Arntzen et al 1974), 5-O-b-D-galactopyranosyl-7-methoxy-3@,4@-dihydroxy-4-phenylcoumarin (Calera et al 1995), piquerol (Mendoza et al 1994), ajmaline (Vallejos and Andreo 1974), DIO-9, leucinostatin and efrapeptin (McCarty et al 1965 ;Lucero et al 1976) as well as several synthetic compounds like, DCCD (McCarty and Racker 1967), N,N-dimethylformamide (Pen8 a-Valdivia et al 1991), triphenyltin chloride (Gould 1976), chlorotri-n-butyltin (Kahn 1976), synthalin (Gross et al 1968) among others, act as energy-transfer inhibitors. Most of these compounds inhibited photophosphorylation by interacting with the H`-ATPase complex but at di †erent levels and with di †erent mechanism of action.…”

Suppression of Lipid Photoperoxidation by Quercetin and Its Glycosides in Spinach Chloroplasts

“…Recently, 0-methyltransferase activities which catalized the stepwise methylation of quercetin and quercetagetin has been found to associate with a spinach chloroplast fraction (Charriere-Ladreix, 1981). A function of flavonols in chloroplasts has been discussed in relation to energy transduction reactions (Arntzen et al, 1974;Muzafarov et al, 1980). Quercetin seems to bind to chloroplast coupling factor and inhibits ATPase activity (Cantley and Hamrnes, 1976).…”