Characterization ofArabidopsisaldolases AtFBA4 and AtFBA5; inhibition by morin and interaction with calmodulin

Fructose bisphosphate aldolases (FBAs) catalyze the reversible cleavage of fructose 1,6-bisphosphate into dihydroxyacetone phosphate and glyceraldehyde 3-phosphate. We analyzed two previously uncharacterized cytosolic Arabidopsis FBAs, AtFBA4 and AtFBA5. Based on a recent report, we examined the interaction of AtFBA4 with calmodulin (CaM)-like protein 11 (AtCML11). AtFBA4 did not bind AtCML11, however, we found that CaM bound AtFBA5 in a Ca 2+ -dependent manner with high specificity and affinity ( K D ∼ 190 nM) and enhanced its stability. AtFBA4 and AtFBA5 exhibited Michaelis-Menten kinetics with K m and V max values of 180 µM and 4.9 U/mg for AtFBA4, and 6.0 µM and 0.30 U/mg for AtFBA5, respectively. The flavonoid morin inhibited both isozymes. Our study suggests that Ca 2+ signalling and flavanols may influence plant glycolysis/gluconeogenesis.