Two different fructokinase isoforms of Arabidopsis thaliana have been ident
ified and characterized by non-denaturing electrophoresis followed by activ
ity-staining. The two fructokinases, fructokinase1 (FRK1) and fructokinase2
(FRK2), showed a high specificity for fructose and did not stain when gluc
ose or mannose were used as substrate. Fructose and ATP at high concentrati
ons (above 5 mM) induced a substrate inhibition of the two enzymatic activi
ties. Arabidopsis FRK1 and FRK2 were capable of employing GTP, CTP, UTP and
TTP as phosphate donors, although with a significantly lower efficiency th
an ATP. The two fructokinase activities were also activated by K+, at aroun
d 10-20 mM, and inhibited by ADP and AMP at concentrations above 10 mM. Fin
ally, FRK1 and FRK2 showed a different expression pattern in the plant, wit
h FRK1 being more abundant in the roots and FRK2 in the shoots. The results
demonstrate a simple technique that provides important information about f
ructokinase activities in the plants and which can be useful for the analys
is of Arabidopsis mutants. (C) 2001 Elsevier Science Ireland Ltd. All right
s reserved.