Hefe‐Phosphofruktokinase : Kinetische Beziehungen zwischen substrat‐ und effectorbindenden Zentren
: Kinetische Beziehungen zwischen substrat‐ und effectorbindenden Zentren
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Media type:
E-Article
Title:
Hefe‐Phosphofruktokinase : Kinetische Beziehungen zwischen substrat‐ und effectorbindenden Zentren
:
Kinetische Beziehungen zwischen substrat‐ und effectorbindenden Zentren
Description:
<jats:p>The kinetic behaviour of different preparations of yeast phosphofructokinase is described, predominantly regarding the interactions between substrate‐ and effector‐binding sites.</jats:p><jats:p>The substrate‐binding site for ATP reacts with ITP and UTP too, whereas the ATP‐inhibitor site possesses higher specifity: other nucleoside triphosphates do not compete with ATP for this site.</jats:p><jats:p>Binding of protons to the enzyme produces a decrease in cooperativity towards fructose‐6‐phosphate with ATP as well as with ITP and UTP as phosphate donors, accompanied by a lowering of the fructose‐6‐phosphate concentration necessary for half‐maximal activity. At the same time the inhibitory action of ATP is descreased.</jats:p><jats:p>AMP is bound to an effector site evidently different from the ATP‐inhibitor site.</jats:p><jats:p>With ITP as phosphate donor, AMP shows no activating effect. AMP decreases the apparent <jats:italic>K<jats:sub>m</jats:sub></jats:italic> value for fructose‐6‐phosphate too without affecting cooperative interactions. Magnesium and ammonium ions are necessary for full enzymatic activity. The latter increases maximal activity and decreases the half‐maximal concentration of fructose‐6‐phosphate.</jats:p><jats:p>Free ATP seems to be a stronger inhibitor for yeast phosphofructokinase than the magnesium‐ATP‐chelate.</jats:p>