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Binding of monofluorophosphate to alpha2-macroglobulin and C3
1Laboratorio de Biología Osea, Facultad de Ciencias Mèdicas, Universidad Nacional de Rosario, Argentina.
Abstract:
After administering an oral dose of monofluorophosphate (MFP) to human beings or rats, a fraction of the drug appears in plasma that is bound to proteins, establishing a previously undetected compartment of nondiffusible fluoride. This article documents experiments performed in vitro, describing the binding of MFP to two plasma globulins: alpha2-macroglobulin and C3 (a beta-globulin). MFP binds irreversibly to these proteins through a stable bond. MFP binds to purified alpha2-macroglobulin or to C3 with a molar ratio MFP: protein close to unity. MFP binding reduces significantly the biological activity of these proteins, which share in common a macrocyclic 4-residue ring thiolactone (Cys-Gly-Glu-Glu). The binding site of MFP is as yet unknown. Protein-bound MFP appeared in the plasma of volunteers during the 5-7 hours following intake. Peak concentration of protein-bound MFP and maximal reduction of alpha2-macroglobulin activity was observed 2 hours after intake. Clearance of protein-bound MFP coincided with the return of alpha2-macroglobulin to basal levels.
Insights
Monofluorophosphate (MFP) irreversibly binds to plasma proteins alpha2-macroglobulin and C3 in humans and rats. This binding reduces protein activity and creates a new, nondiffusible fluoride compartment in plasma.
Area of Science:
- Biochemistry
- Pharmacology
- Toxicology
Background:
- Monofluorophosphate (MFP) is administered orally.
- A fraction of MFP appears in plasma bound to proteins.
- This protein-bound fraction represents a previously undetected compartment of nondiffusible fluoride.
Purpose of the Study:
- To document in vitro experiments describing MFP binding to plasma globulins.
- To investigate the nature of MFP binding to alpha2-macroglobulin and C3.
- To assess the impact of MFP binding on protein biological activity.
Main Methods:
- In vitro experiments were conducted to study MFP binding.
- Purified alpha2-macroglobulin and C3 (a beta-globulin) were used.
- Molar ratios of MFP to protein binding were determined.
Main Results:
- MFP binds irreversibly to alpha2-macroglobulin and C3 via a stable bond.
- The molar ratio of MFP:protein binding is close to unity.
- MFP binding significantly reduces the biological activity of these proteins.
- Protein-bound MFP was detected in human plasma 5-7 hours post-intake.
- Peak protein-bound MFP and reduced alpha2-macroglobulin activity occurred 2 hours post-intake.
Conclusions:
- MFP forms a stable, nondiffusible fluoride compartment in plasma through irreversible protein binding.
- The binding affects the biological function of key plasma proteins.
- Further research is needed to identify the specific MFP binding site on these proteins.