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Polyamines stimulate the binding of hexokinase type II to mitochondria
Abstract:
Spermine and spermidine enhanced the binding of hexokinase isoenzyme type II to mitochondria, both of which were prepared from Ehrlich-Lettre hyperdiploid ascites tumor cells, at much lower concentrations than Mg2+. Chymotrypsin-treated hexokinase II could not bind to the mitochondrial membrane in the presence of either spermine or Mg2+, indicating that the effect of spermine is not a nonspecific action, since the treatment of chymotrypsin cleaves only the region essential for the binding without any significant effect of the catalytic activity. Both spermine and Mg2+ antagonized the glucose 6-phosphate-induced release of mitochondria-bound hexokinase, and promoted the binding of the solubilized hexokinase II even in the presence of glucose 6-phosphate. However, inhibition of the activity of soluble hexokinase by glucose 6-phosphate was not reversed by spermine and Mg2+. Hexokinase II rebound to mitochondria with spermine and Mg2+ produced glucose 6-phosphate using ATP generated inside the mitochondria, and no difference was observed between the spermine- and Mg2+-rebound systems. Significance of the binding of hexokinase to mitochondria, especially with polyamines, is discussed with reference to high glycolytic rate in tumor cells.
Insights
Spermine and spermidine enhance hexokinase II binding to mitochondria in tumor cells, similar to Mg2+. This binding is crucial for high glycolytic rates in cancer and is not a non-specific action.
Area of Science:
- Biochemistry
- Cell Biology
- Oncology
Background:
- Hexokinase isoenzyme type II (HKII) plays a critical role in cellular glucose metabolism.
- Mitochondrial HKII binding is linked to increased glycolysis, a hallmark of cancer cells.
- The precise mechanisms regulating HKII-mitochondria interaction are not fully understood.
Purpose of the Study:
- To investigate the role of polyamines, specifically spermine and spermidine, in regulating the binding of hexokinase II to mitochondria.
- To compare the effects of polyamines with magnesium ions (Mg2+) on HKII-mitochondria interactions.
- To elucidate the functional significance of polyamine-mediated HKII binding in tumor cells.
Main Methods:
- Preparation of hexokinase isoenzyme type II and mitochondria from Ehrlich-Lettre ascites tumor cells.
- Assessment of HKII binding to mitochondria using varying concentrations of spermine, spermidine, and Mg2+.
- Enzymatic assays to evaluate the activity of soluble and mitochondria-bound hexokinase.
- Chymotrypsin treatment of hexokinase II to probe the binding site.
Main Results:
- Spermine and spermidine significantly enhanced HKII binding to mitochondria at lower concentrations than Mg2+.
- Chymotrypsin treatment abolished spermine- and Mg2+-mediated binding, indicating a specific interaction.
- Both spermine and Mg2+ prevented glucose 6-phosphate-induced release of bound HKII and promoted binding of solubilized HKII.
- Spermine and Mg2+ did not reverse the glucose 6-phosphate inhibition of soluble hexokinase activity.
- Rebound hexokinase II, facilitated by spermine or Mg2+, produced glucose 6-phosphate using mitochondrial ATP.
Conclusions:
- Polyamines like spermine and spermidine are potent regulators of hexokinase II binding to mitochondria.
- This interaction is specific and plays a role in maintaining high glycolytic rates in tumor cells.
- The findings suggest a novel mechanism involving polyamines in cancer cell energy metabolism.