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Human placental ATP-diphosphohydrolase: biochemical characterization, regulation and function
A M Kettlun1, A Alvarez, R Quintar
1Departmento de Bioquímica y Biología Molecular, Facultad de Ciencias Químicas y Farmacéuticas, Universidad de Chile, Santiago.
The International Journal of Biochemistry
|March 1, 1994
Summary
Human placental apyrase (ATP-diphosphohydrolase) was characterized, revealing its role in inhibiting platelet aggregation. This enzyme
Area of Science:
- Biochemistry
- Enzymology
- Molecular Biology
Background:
- Human placental microsomes exhibit ATPase and ADPase activities.
- These activities were previously uncharacterized regarding their specific enzyme source.
Purpose of the Study:
- To identify and characterize the enzyme responsible for ATPase and ADPase activities in human placental microsomes.
- To elucidate the kinetic properties, essential amino acid residues, and potential in vivo function of this enzyme.
Main Methods:
- Kinetic and physico-chemical analyses of human placental microsomal fraction.
- Enzyme purification and characterization.
- Interaction studies with modulatory proteins and inhibitors.
- Assessment of effects on washed platelets.
Main Results:
- ATPase and ADPase activities were confirmed to be from ATP-diphosphohydrolase (apyrase, EC 3.6.1.5).
- The enzyme hydrolyzes nucleotide complexes with higher efficiency and is insensitive to ouabain and Ap5A.
- Apyrase is a glycoprotein, inhibited by o-vanadate, DES, and DCCD, with Arg, Lys, and His residues being essential.
- Activating and inhibitory proteins modulating apyrase activity were identified in placental tissue.
Conclusions:
- Human placental apyrase is a glycoprotein with specific kinetic properties and essential amino acid residues.
- The enzyme's ADPase activity suggests a role in inhibiting platelet aggregation in vivo.
- Further research into modulatory proteins could reveal novel therapeutic targets.