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Interference by ATPase in the assay of rat heart phosphofructokinase
Insights
A novel high molecular-weight protein in heart extracts activates phosphofructokinase by hydrolyzing ATP. This ATPase activity modulates enzyme regulation, distinct from adrenergic/Ca2+ signaling pathways.
Area of Science:
- Biochemistry
- Enzymology
- Cardiac Physiology
Background:
- Phosphofructokinase (PFK) is a key regulatory enzyme in glycolysis.
- Cardiac metabolism involves complex regulatory mechanisms for enzymes like PFK.
- Understanding PFK regulation is crucial for cardiac energy homeostasis.
Purpose of the Study:
- To identify and characterize a novel activator of cardiac phosphofructokinase.
- To elucidate the mechanism by which this protein affects PFK activity.
- To determine the relationship between this activator and known regulatory pathways.
Main Methods:
- Gel-exclusion chromatography and high-speed centrifugation for protein isolation.
- Enzyme assays to measure phosphofructokinase activity.
- ATP hydrolysis assays to investigate the mechanism of activation.
- Experiments using Mn2+ to probe the role of the ATPase activity.
Main Results:
- A high molecular-weight protein with ATPase activity was isolated from heart extracts.
- This protein activates phosphofructokinase through ATP hydrolysis to ADP, AMP, and inorganic phosphate.
- Activation is inhibited by Mn2+.
- The ATPase-mediated activation mechanism differs from adrenergic/Ca2+-dependent regulation.
Conclusions:
- A novel cardiac protein modulates phosphofructokinase activity via ATP hydrolysis.
- This mechanism represents a distinct regulatory pathway for cardiac glycolysis.
- The Mn2+-sensitive ATPase is not involved in adrenergic/Ca2+-mediated cardiac PFK control.
Abstract:
A high molecular-weight protein was found in heart extracts which, in the assay for phosphofructokinase, artificially activated the enzyme. The protein could be removed by gel-exclusion chromatography or high-speed centrifugation. The mechanism of activation appeared to be due to the hydrolysis of ATP to ADP, AMP and inorganic phosphate which was inhibited by Mn2+. Phosphofructokinase is thus activated by the production of activators and by the lowered inhibitory concentration of ATP. Since the adrenergic/Ca2+-activated form of the enzyme is the more sensitive to activators, the difference between the two forms of phosphofructokinase is amplified in the presence of the ATPase and diminished upon its removal or its inhibition by Mn2+. The Mn2+-sensitive ATPase appears to play no part in the adrenergic/Ca2+-mediated control of cardiac phosphofructokinase or the interconverting reactions.
