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A monoclonal antibody against horse kidney (Na+ + K+)-ATPase inhibits sodium pump and E2K to E1 conversion of (Na+ + K+)-ATPase from outside of the cell membrane

1989; Elsevier BV; Volume: 994; Issue: 2 Linguagem: Inglês

10.1016/0167-4838(89)90149-0

1878-1454

Kanako Satoh, Toshiko Nakao, Fumiko Nagai, Itsu Kano, Atsuko Nakagawa, Keiko Ushiyama, Osamu Urayama, Yukichi Hara, Makoto Nakao,

Pancreatic function and diabetes

Monoclonal antibodies against horse kidney outer medulla (Na+ + K+)-ATPase were prepared. One of these antibodies (M45–80), was identified as an IgM, recognized the α subunit of the enzyme. M45–80 had the following effects on horse kidney (Na+ + K+)-ATPase; (1) it inhibited the enzyme activity by 50% in 140 mM Na+ and by 80% in 8.3 mM Na+; (2) it increased the Na+ concentration necessary for half-maximal activation (K0.5for Na+) from 12.0 to 57.6 mM, but did not affect K0.5 for K+; (3) it slightly increased the K+-dependent p-nitrophenylphosphatase (K-pNPPase) activity; (4) it inhibited phosphorylation of the enzyme with ATP by 30%, but did not affect the step of dephosphorylation; and (5) it enhanced the ouabain binding rate. These data are compatible with a stabilizing effect on the E2 form of (Na+ + K+)-ATPase. M45–80 was concluded to binf to the extracellular surface of the plasmamembrane, based on the following evidence: (1) M45–80 inhibited by 50% the ouabain-sensitive86Rb+ uptake in human intact erythrocytes from outside of the cells; (2) the inhibition of (Na+ + K+)-ATPase activity in right-side-out vesicles of human erythrocytes was greater than that in inside-out vesicles; and (3) the fluorescence intensity due to FITC-labeled rabbit anti-mouse IgM that reacted with M45–80 bound to the right-side-out vesicles was much greater than that in the case of the inside-out vesicles.