title: Flavonoids as inhibitors of NADP-malic enzyme and PEP carboxylase from C4 plants.
abstract: The inhibitory effects of flavonoids on the activity of two photosynthetic enzymes such as phosphoenolpyruvate carboxylase (PEPCase) and NADP-dependent malic enzyme (NADP-ME) were evaluated. The glycosylation of hydroxyl groups on the flavonoids resulted in compounds that behaved as gradually weaker inhibitors with increased size of the substituent. Quercetin and baicalein showed a competitive inhibition pattern vs. NADP+ for NADP-ME, and a similar model for both flavonoids vs. phosphoenolpyruvate (PEP) was observed when tested on PEPCase. K(i) for NADP-ME inhibition at pH 7.0 were 0.83 microM and 1.54 microM for quercetin and baicalein, respectively. K(i) for PEPCase inhibition were 0.17 microM and 0.79 microM (quercetin and baicalein, respectively), indicating that these compounds are the most potent inhibitors described for this carboxylase. I50 values for these and other flavonoids were in the micromolar range. A tentative physiological role for the inhibitory effects observed on PEPCase is discussed.
authors.affiliation: Centro de Estudios Fotosintéticos y Bioquímicos (CEFOBI, CONICET-Fund M. Lillo), Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Argentina.
authors.forename: C F
authors.initials: CF
authors.lastname: Pairoba
authors.forename: S L
authors.initials: SL
authors.lastname: Colombo
authors.forename: C S
authors.initials: CS
authors.lastname: Andreo
mesh_terms: D004791:Enzyme Inhibitors / Q000737:chemistry / Q000494:pharmacology*; D044950:Flavanones; D005419:Flavonoids / Q000737:chemistry / Q000494:pharmacology*; D006031:Glycosylation; D006863:Hydrogen-Ion Concentration; D019684:Magnoliopsida / Q000201:enzymology; D008291:Malate Dehydrogenase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D010730:Phosphoenolpyruvate Carboxylase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D010940:Plant Proteins / Q000378:metabolism; D011794:Quercetin / Q000031:analogs & derivatives / Q000737:chemistry / Q000494:pharmacology; D012431:Rutin / Q000737:chemistry / Q000494:pharmacology; D013329:Structure-Activity Relationship; D003313:Zea mays / Q000201:enzymology
chemical_list: D004791:Enzyme Inhibitors; D044950:Flavanones; D005419:Flavonoids; D010940:Plant Proteins; C012526:quercitrin; C038044:baicalin; C006680:baicalein; D012431:Rutin; D011794:Quercetin; D008291:Malate Dehydrogenase; C031917:malate dehydrogenase (oxaloacetate-decarboxylating) (NADP+); D010730:Phosphoenolpyruvate Carboxylase