Characteristics of adenylyl imidodiphosphate- and ADP-binding sites insoluble and particulate mitochondrial ATPase. Studies with methanol
Related Experiment Videos
Abstract:
The characteristics of the binding sites for ADP and adenylyl imidodiphosphate have been studied in soluble and particulate F1-ATPase from bovine heart mitochondria. ADP, but not electrochemical gradients, removes the inhibitory effect of adenylyl imidodiphosphate on ATPase activity in coupled submitochondrial particles. In soluble F1-ATPase, methanol at 20% concentration diminishes the ability of ATP and adenylyl imidodiphosphate to inhibit ATP and ITP hydrolysis; these findings suggest that ADP and adenylyl imidodiphosphate inhibit hydrolysis by acting on the same site. Methanol at 20% stimulates the hydrolytic activity of soluble F1-ATPase, but fails to stimulate significantly the activity of the particulate enzyme, even though in particulate F1-ATPase methanol markedly diminishes the inhibiting action of added ADP and adenylyl imidodiphosphate on ATP and ITP hydrolysis. This is consistent with the idea that in the particulate system there are two inhibitory binding sites for ADP, one accessible to methanol, and another which is inaccessible to methanol; the latter is transitorily occupied by ADP arising from ATP hydrolysis. Indeed, experiments on the effect of ADP in ITP hydrolysis by submitochondrial particles show the existence of two ADP inhibitory sites.
Insights
Adenosine diphosphate (ADP) and adenylyl imidodiphosphate bind to distinct sites on soluble F1-ATPase, but share a common inhibitory site on particulate F1-ATPase, suggesting complex regulatory mechanisms in mitochondrial energy production.
Area of Science:
- Biochemistry
- Mitochondrial Physiology
- Enzyme Kinetics
Background:
- F1-ATPase is crucial for ATP synthesis and hydrolysis in mitochondria.
- Understanding the binding characteristics of inhibitors like ADP and adenylyl imidodiphosphate is key to elucidating enzyme regulation.
- Mitochondrial F1-ATPase exists in both soluble and particulate forms, with potentially different regulatory properties.
Purpose of the Study:
- To investigate the binding characteristics of ADP and adenylyl imidodiphosphate in soluble and particulate F1-ATPase.
- To determine the relationship between ADP and adenylyl imidodiphosphate inhibition.
- To explore the role of methanol in modulating F1-ATPase activity and inhibitor binding.
Main Methods:
- Studying the ATPase activity of soluble and particulate F1-ATPase from bovine heart mitochondria.
- Utilizing adenylyl imidodiphosphate and ADP as inhibitors.
- Employing 20% methanol to probe inhibitor binding site accessibility.
- Assessing inhibition of ATP and ITP hydrolysis.
Main Results:
- In coupled submitochondrial particles, ADP, not electrochemical gradients, reverses adenylyl imidodiphosphate inhibition.
- In soluble F1-ATPase, methanol diminishes the inhibitory effects of both ATP and adenylyl imidodiphosphate, suggesting a shared binding site.
- Methanol stimulates soluble F1-ATPase but not particulate F1-ATPase, and reduces inhibitor action in the particulate form, indicating distinct binding sites.
Conclusions:
- ADP and adenylyl imidodiphosphate likely inhibit soluble F1-ATPase at the same site.
- Particulate F1-ATPase exhibits two distinct inhibitory ADP binding sites, one accessible and one inaccessible to methanol.
- The inaccessible site is transiently occupied by ADP generated during ATP hydrolysis, highlighting a feedback mechanism.