THE EFFECT OF LANTHANIDES ON THE ACTIVITY OF FRUCTOSE-1,6-BISPHOSPHATASE

In the present study, we analyze the effect of lanthanides on the activity of fructose-1,6-bisphosphatase obtained from spinach chloroplasts and Anabaena 7119. When the hydrolysis of fructose 1,6-bisphosphate was assayed at high concentrations of both fructose 1, 6-bisphosphate and Mg2-, the rate was inhibited at low concentrations of La3+, Eu3+, and .Tb3+; the concentrations that yielded half of the initial activity (I0.5) were 0.25 uM, 0.25 uM, and 0.50 uM, respectively. Apparently, the modification of kinetic constants did not correlate with electronic characteristics of rare earths elements (ionic radii). On the other hand, the fructose- 1,6-bisphosphatase obtained from the cyanobacteria was also inhibited by Tb3+; however, the concentration required for similar inhibition was much higher (I0.5,=2.0 mM). On this basis, although the cyanobacterial and the chloroplast enzyme belong to the same metabolic pathway (the reductive pentose phosphate cycle), the mechanism by which cations regulate the enzyme activity was different.