title: Monoclonal antibody to phosphatidylserine inhibits Na+/K(+)-ATPase activity.
abstract: A monoclonal IgG, directed to phosphatidylserine (PS1G3), partially (40-50%) inhibited Na+/K(+)-ATPase activity (forward running reaction cycle) without affecting the K0.5 values for Na+,K+ and MgATP. The Hill or interaction coefficients (nH) for Na+ and K+ for this reaction were reduced from 3.0 to 1.6 and from 1.6 to 0.8, respectively. The K(+)-stimulated p-nitrophenylphosphatase activity (p-NPPase), which is a partial reaction sequence of the Na+/K(+)-ATPase system (but in the backward running mode), was inhibited more strongly (about 70%) due to an increase in K+/substrate antagonism. In this system K0.5 and nH values for both p-nitrophenyl phosphate (p-NPP) and K+ were increased by the mAb. At the maximally inhibitory concentration of PS1G3 the Vmax of the p-NPPase was also reduced. Partial reactions, which were inhibited by PS1G3, are: (1) the Na(+)-activated phosphorylation (non-competitive vs. Na+), (2) the Rb+ occlusion (competitive vs. Rb+). Partial reactions not harmed by PS1G3 are: (3) the K(+)-dependent dephosphorylation, (4) the K(+)-dependent E1 + K+<-->E2K transition. We conclude that PtdSer is involved in cation occlusion, possibly by forming part of the access gate.
authors.affiliation: Department of Biochemistry, University of Nijmegen, The Netherlands.
authors.forename: F M
authors.initials: FM
authors.lastname: Stekhoven
authors.forename: J
authors.initials: J
authors.lastname: Tijmes
authors.forename: M
authors.initials: M
authors.lastname: Umeda
authors.forename: K
authors.initials: K
authors.lastname: Inoue
authors.forename: J J
authors.initials: JJ
authors.lastname: De Pont
mesh_terms: D009597:4-Nitrophenylphosphatase / Q000037:antagonists & inhibitors; D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D000937:Antigen-Antibody Reactions; D007679:Kidney Medulla / Q000201:enzymology; D007700:Kinetics; D051379:Mice; D008807:Mice, Inbred BALB C; D010718:Phosphatidylserines / Q000276:immunology*; D010766:Phosphorylation; D011189:Potassium Chloride / Q000494:pharmacology; D011817:Rabbits; D012965:Sodium Chloride / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors* / Q000302:isolation & purification
chemical_list: D000911:Antibodies, Monoclonal; D010718:Phosphatidylserines; D012965:Sodium Chloride; D011189:Potassium Chloride; D009597:4-Nitrophenylphosphatase; D000254:Sodium-Potassium-Exchanging ATPase