Hefe-Phosphofructokinase.

The effect of trypsin treatment with respect to the allosteric properties of yeast phosphofructokinase as well as its molecular weight has been studied. In the presence of fructose 6-phosphate trypsin desensitizes yeast phosphofructokinase to ATP inhibition. Under the same conditions, activation of this enzyme by the positive allosteric effector AMP, however, remains uneffected. Addition of MgATP instead of fructose 6-phosphate to the incubation medium containing trypsin protects the enzyme against ATP-desensitization. After prolonged incubation of yeast phosphofructokinase with trypsin the enzyme becomes inactivated both with fructose-6-phosphate and with MgATP. Using density gradient centrifugation sucrose media the effects of trypsin treatment on the sedimentation behaviour of yeast phosphofructokinase has also been investigated. With fructose 6-phosphate, trypsin converts the 560000 form of yeast phosphofructokinase into two enzymatically active forms of 510000 and 350000 daltons respectively, which are both e to ATP inhibition. On the other hand, in the presence of MgATP the peak of enzymatic activity sediments with 160000 daltons. This molecular form has the same high sensitivity to ATP inhibition as the untreated enzyme of molecular weight 560000. After the addition of fructose 6-phosphate, the 160000-molecule seems to dimerize giving an ATP-sensitive form with a molecular weight of 340000. In the light of studies about the existence of several interconvertible forms of yeast phosphofructokinase published recently by our laboratory, the results described in this paper are discussed in terms of the existence of dimeric and trimeric states, regarding the 16000-moiety as the trypsin modified monomer of the enzyme. Kinetic and allosteric properties of these states including conditions for their formation and stabilization are summarized and the peculiarities of the trypsin-unmodified and trypsin-modified enzyme are compared. [ABSTRACT FROM AUTHOR]