Human placental atp-diphosphohydrolase: Biochemical characterization,regulation and function |
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| Institution: | 2. Departmento de Hematología, Facultad de Medicina, Pontificia Universidad Católica, Santiago, Chile;1. School of Life Sciences, Fujian Agriculture and Forestry University, Fuzhou, 350002, Fujian, China;2. FAFU-UCR Joint Center and Fujian Provincial Key Laboratory of Haixia Applied Plant Systems Biology, Haixia Institute of Science and Technology, Fujian Agriculture and Forestry University, Fuzhou, 350002, Fujian, China;3. Division of Biological Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi, 464-8602, Japan;4. Gregor Mendel Institute of Molecular Plant Biology GmbH Dr, Bohr-Gasse 3, 1030, Vienna, Austria;5. Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi, 464-8601, Japan;1. Department of Biological and Chemical Sciences, Illinois Institute of Technology, 3101S Dearborn ST., Chicago, IL 60616, United States;2. Department of Obstetrics and Gynecology, University of Illinois at Chicago, 820 S Wood Street, M/C 808, Chicago, IL 60612, United States;1. University of Houston, 4800 Calhoun Rd., Houston, TX 77004, USA;2. University of California, Riverside, 900 University Ave., Riverside, CA 92521, USA |
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| Abstract: | - 1.1. Kinetic and physico-chemical studies on human placental microsomal fraction confirmed that the ATPase and ADPase activities detected in this fraction correspond to the enzyme ATP-diphosphohydrolase or apyrase (EC 3.6.1.5). These include substrate specificity, and coincident Mr and pI values of both ATPase-ADPase activities.
- 2.2. This enzyme hydrolyses both the free unprotonated and cation-nucleotide complex, the catalytic efficiency for the latter being considerably higher.
- 3.3. Microsomal apyrase is insensitive to ouabain and Ap5A. The highly purified enzyme was only inhibited by o-vanadate, DBS and slightly by DCCD.
- 4.4. Apyrase seems to be a glycoprotein from its interaction with Concanavalin-A.
- 5.5. Preliminary studies on the essential amino acid residues suggest the participation of Arg, Lys and His residues, and discard the requirement of −SH, COO−, −OH, and probably also Tyr and Trp.
- 6.6. Two kinetic modulatory proteins of apyrase were detected in placental tissue. An activating protein was found in the soluble fraction and an inhibitory protein was loosely bound to the membranes.
- 7.7. The proposed in vivo function for apyrase is related to the inhibition of platelet aggregation due to its ADPase activity, which is supported by the direct effect on washed platelets and by its plasma membrane localization.
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