Purification and characterization of phosphofructokinase from the yeast Kluyveromyces lactis

Phosphofructokinase from Kluyveromyces lactis was purified by 180‐fold enrichment, elaborating the following steps: cell disruption, polyethylene glycol precipitation, affinity chromatography, size exclusion chromatography on Sepharose 6B and on Bio‐Sil SEC 400 and ion exchange chromatography. The homogeneous enzyme exhibits a molecular mass of 845±20 kDa as determined by sedimentation equilibrium measurements and a specific activity of 100 units/mg protein. The apparent sedimentation coefficient was found to be s20,C=20·7±0·6 S and no significant dependence on the protein concentration was observed in a range from 0·2 to 8 mg protein/ml. Sodium dodecyl sulfate–polyacrylamide gel electrophoresis revealed two bands corresponding to molecular masses of 119±5 kDa and 102±5 kDa, respectively. Thus, the enzyme assembles as octamer composed of two types of subunits. From Western blot analysis applying subunit‐specific monoclonal antibodies raised against Saccharomyces cerevisiae phosphofructokinase and from the determination of the N‐terminal amino acid sequence, the conclusion was drawn that the 102 kDa‐subunit corresponds to the β‐subunit of the S. cerevisiae enzyme. In contrast to bakers' yeast phosphofructokinase, the K. lactis enzyme exhibits no cooperativity with respect to the substrate fructose 6‐phosphate. Both activators AMP and fructose 2,6‐bisphosphate decrease the Michaelis constant with respect to this substrate. The enzyme from K. lactis is also inhibited by ATP. Fructose 2,6‐bisphosphate or AMP diminish the ATP‐inhibition. In contrast to the phosphofructokinase from S. cerevisiae, where fructose 2,6‐bisphosphate turned out to be more efficient than AMP, both activators exert similar effects on the K. lactis enzyme. © 1997 John Wiley & Sons, Ltd.