Characterization of Arabidopsis aldolases AtFBA4, AtFBA5, and their inhibition by morin and interaction with...

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 Ca²⁺-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^-1 for AtFBA4, and 6.0 μm and 0.30 U·mg^-1 for AtFBA5, respectively. The flavonoid morin inhibited both isozymes. Our study suggests that Ca²⁺ signaling and flavanols may influence plant glycolysis/gluconeogenesis.