An allosteric phosphofructokinase (PFK) was created by sequence manipulation of the nonallosteric enzyme from the slime mold Dictyostelium discoideum (DdPFK). Most amino acid residues proposed as important for catalytic and allosteric sites are conserved in DdPFK except for a few of them, and their reversion did not modify its kinetic behavior. However, deletions at the unique C-terminal extension of this PFK produced a markedly allosteric enzyme. Thus, a mutant lacking the last 26 C-terminal residues exhibited hysteresis in the time course, intense cooperativity (nH = 3.8), and a 200-fold decrease in the apparent affinity for fructose 6-phosphate (S0.5 = 4500 μm), strong activation by fructose 2,6-bisphosphate (Kact = 0.1 μm) and fructose 1,6.bisphosphate (Kact = 40 μm), dependence on enzyme concentration, proton inhibition, and subunit association-dissociation in response to fructose 6-phosphate versus the nonhysteretic and hyperbolic wild-type enzyme (nH = 1.0; Km = 22 μM) that remained as a stable tetramer. Systematic deletions and point mutations at the C-tail region of DdPFK identified the last C-terminal residue, Leu834, as critical to produce a nonallosteric enzyme. All allosteric mutants were practically insensitive to MgATP inhibition, suggesting that this effect does not involve the same allosteric transition as that responsible for fructose 6-phosphate cooperativity and fructose bisphosphate activation.

This work was supported by Grants PB95-0209 and PB98-0058 from the Dirección General de Enseñanza Superior e Investigación Científica.

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