FRU 2,6-P-2 AND CITRATE - INTRACELLULAR-DISTRIBUTION IN CITRUS TISSUES AND EFFECT ON GRAPEFRUIT LEAF PFP

Grapefruit leaf PFP was studied for its activation by fructose 2,6-bis phosphate (Fru 2,6-P-2) in the forward and reverse reactions. In the g lycolytic reaction, a Ka of 4.0 +/- 0.12 nM was obtained. This constan t is affected by the presence of increasing concentrations of citrate (1, 5 and 20 mM) with a Ka(citrate) of 4.5 +/- 0.09, 6.9 +/- 0.05 and 38.2 +/- 1.4 respectively. The inhibition mode of citrate is competiti ve with Fru 2,6-P-2, but non-linear in relation of increasing concentr ations of the inhibitor. The intracellular distribution and concentrat ion of the key regulatory metabolite Fru 2,6-P-2 was further investiga ted in citrus leaves and juice cells. Fru 2,6-P-2 was only found in th e cytosol of juice cells. Fru 2,6-P-2 was detected under both conditio ns with higher concentrations found under aerobiosis.