Characterization of yeast fructose-2,6-bisphosphate 6-phosphatase

To obtain information on the biological significance of yeast fructose-2,6-bisphosphate 6-phosphatase, kinetic data of the purified enzyme [(1987) Eur. J. Biochem. 164, 27-30] have been measured. Maximal activity was found between pH 6 and 7, the apparent Michaelis constant with fructose 2,6-bisphosphate was 7.2 microM at pH 6.0 and 79 microM at pH 7.0. Concentrations required for 50% inhibition of the enzyme at pH 6.0 were 8 microM Fru2P, 45 microM G1c6P, 80 microM Fru6P and 200 microM inorganic phosphate. The known intracellular steady-state level of about 10 microM fructose 2,6-bisphosphate in the presence of glucose is likely to be the result of a balance between the rapid synthesis of fructose 2,6-bisphosphate catalyzed by 6-phosphofructose 2-kinase and a fructose 2,6-bisphosphate degrading activity. The biological function of fructose-2,6-bisphosphate 6-phosphatase with an apparent Michaelis constant between 7 and 79 microM fructose 2,6-bisphosphate at pH 6-7 is therefore suggested to participate in the maintenance of a steady-state level of fructose 2,6-bisphosphate in a concentration range that fits well with the Michaelis constant of the enzyme.