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Mitochondrial hexokinase from small-intestinal mucosa and brain
Abstract:
1. The submitochondrial localization of hexokinase activity in preparations of mitochondria from the small intestine of the guinea pig was studied by conventional methods. 2. Hexokinase activity in this tissue was predominantly associated with the outer mitochondrial membrane. 3. The inactivation of mitochondrial enzymes by trypsin in iso-osmotic and hypo-osmotic conditions was also used to determine the submitochondrial localization of hexokinase activity. 4. Hexokinase activity was found to be on the outside of the outer mitochondrial membrane. 5. It was shown that both type I and type II hexokinase activities are bound to the outside of the outer mitochondrial membrane. The types are present in the same ratio as that in which they occur in the cytosol of the cell. 6. Mitochondrial hexokinase from the small intestine did not show the latency phenomenon demonstrated by mitochondrial hexokinase from brain when subjected to a variety of treatments. However, hexokinase activity was solubilized from preparations of mitochondria from the small intestine by the same treatments as for mitochondrial hexokinase from brain. 7. The submitochondrial distribution of hexokinase activity in mitochondrial preparations from rat brain was determined by the trypsin inactivation method. 8. Hexokinase activity in preparations of mitochondria from rat brain was found on the outside of the outer membrane, between the mitochondrial membranes, and within the inner mitochondrial membrane. 9. Hexokinase from rat brain showed latency properties irrespective of its submitochondrial location.
Insights
Hexokinase activity in guinea pig small intestine mitochondria is primarily on the outer membrane. This contrasts with rat brain mitochondria, where hexokinase is found in multiple locations and exhibits latency.
Area of Science:
- Mitochondrial biochemistry
- Enzyme localization
- Cellular metabolism
Background:
- Hexokinase (EC 2.7.1.1) is a key enzyme in glucose metabolism.
- Its submitochondrial localization can influence cellular energy production.
- Previous studies suggested varied hexokinase distribution in different tissues.
Purpose of the Study:
- To determine the submitochondrial localization of hexokinase activity in guinea pig small intestine mitochondria.
- To compare this localization with that of hexokinase in rat brain mitochondria.
- To investigate the properties of mitochondrial hexokinase in these tissues.
Main Methods:
- Conventional biochemical methods for enzyme activity assays.
- Trypsin inactivation of mitochondrial enzymes under varying osmotic conditions.
- Solubilization of enzyme activity using specific treatments.
Main Results:
- Hexokinase activity in guinea pig small intestine mitochondria is predominantly associated with the outer mitochondrial membrane, specifically on the external surface.
- Both hexokinase type I and type II were found bound to the outer mitochondrial membrane in the same ratio as in the cytosol.
- Mitochondrial hexokinase from the small intestine did not exhibit latency, unlike that from rat brain, though it could be solubilized similarly.
Conclusions:
- Hexokinase is primarily localized to the outer mitochondrial membrane in the guinea pig small intestine.
- Submitochondrial localization and latency properties of hexokinase differ significantly between small intestine and brain mitochondria.
- These differences may reflect tissue-specific roles in glucose metabolism.