FRUCTOSEBISPHOSPHATASE ISOENZYMES OF THE CHEMOAUTOTROPH XANTHOBACTER-FLAVUS

Xanthobacter flavus employs two fructosebisphosphatase (FBPase)-sedohe ptulosebisphosphatase (SBPase) enzymes. One of these is constitutively expressed and has a high FBPase-to-SBPase ratio. The alternative enzy me, which is encoded by cbbF, is induced during autotrophic growth, Th e cbbF gene was expressed in Escherichia coli, and the FBPase was puri fied to homogeneity. The purified enzyme has a specific FBPase activit y of 114 mu mol/min/mg of protein, a Michaelis constant for fructosebi sphosphate of 3 mu M, and a low FBPase-to-SBPase ratio. CbbF was activ ated by ATP and inhibited by Ca2+.