PMID: 9393Sep 25, 1976

Phosphofructokinase. I. Mechanism of the pH-dependent inactivation and reactivation of the rabbit muscle enzyme

The Journal of Biological Chemistry
P E Bock, C Frieden

Abstract

The kinetics of inactivation and reactivation of rabbit skeletal muscle phosphofructokinase have been studied as a function of pH and enzyme concentration at constant temperature in phosphate buffer. From the enzyme concentration dependence, we conclude that the minimal mechanism for inactivation involves a protonation step followed by isomerization to an inactive form and then dissociation to a species of one-half the molecular weight. Other data indicate a subsequent isomerization of the dissociated form. The pH and temperature dependence of the inactivation process shows that it is controlled by ionizable groups, and that the apparent pK for these groups is temperature-dependent in such a way as to make the enzyme show the characteristic of cold lability below pH 7. Reactivation of the inactive enzyme occurs by a kinetically different pathway involving deprotonation of an inactive, dissociated form to a form which may either isomerize to another inactive form, or dimerize to the active enzyme. A general mechanism is postulated in which the inactivation and reactivation processes are different aspects of the same mechanism. This mechanism assumes four species (two containing four subunits and two containing two subunits) each...Continue Reading

Related Concepts

Biochemical Pathway
Phosphate buffers
Phosphofructokinase
Muscle
Specimen Type - Skeletal Muscle
6-Phosphofructokinase
Muscle Enzyme
Hydrogen-Ion Concentration
Enzyme Activation
Skeletal Muscle Structure

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