TAILIEUCHUNG - Báo cáo khoa học: Stimulation of p-nitrophenylphosphatase activity of Na+ ⁄ K+-ATPase by NaCl with oligomycin or ATP

It is known that the addition of NaCl with oligomycin or ATP stimulates ouabain-sensitive and K + -dependent p-nitrophenylphosphatase (pNPPase) activity of Na + ⁄K + -ATPase. We investigated the mechanism of the stimu-lation. The combination of oligomycin and NaCl increased the affinity of pNPPase activity for K + . When the ratio of Na + to Rb + was 10 in the presence of oligomycin, Rb + -binding and pNPPase activity reached a maxi-mal level and Na + was occluded. | ềFEBS Journal Stimulation of p-nitrophenylphosphatase activity of Na K -ATPase by NaCl with oligomycin or ATP Haruo Homareda1 and Makoto Ushimaru2 1 Department of Biochemistry Kyorin University Schoolof Medicine Mitaka Tokyo Japan 2 Department of Chemistry Kyorin University Schoolof Medicine Mitaka Tokyo Japan Keywords diprotomer Na K -ATPase oligomycin p-nitrophenylphosphate pNPP p-nitrophenylphosphatase pNPPase Correspondence H. Homareda Department of Biochemistry Kyorin University Schoolof Medicine Mitaka Tokyo 181-8611 Japan Fax Tel 81 422 76 7651 E-mail homareda@ Received 5 July 2004 revised 24 October 2004 accepted 19 November 2004 doi It is known that the addition of NaCl with oligomycin or ATP stimulates ouabain-sensitive and K -dependent p-nitrophenylphosphatase pNPPase activity of Na K -ATPase. We investigated the mechanism of the stimulation. The combination of oligomycin and NaCl increased the affinity of pNPPase activity for K . When the ratio of Na to Rb was 10 in the presence of oligomycin Rb -binding and pNPPase activity reached a maximal level and Na was occluded. Phosphorylation of Na K -ATPase by p-nitrophenylphosphate pNPP was not affected by oligomycin. Because oligomycin stabilizes the Na -occluded El state of Na K -ATPase. it seemed that the Na -occluded E1 state increased the affinity of the phosphoenzyme formed from pNPP for K . On the other hand the combination of ATP and NaCl also increased the affinity of pNPPase for K and activated ATPase activity. Both activities were affected by the ligand conditions. Oligomycin noncompetitively affected the activation of pNPPase by NaCl and ATP. Nonhydrolyzable ATP analogues could not substitute for ATP. As NaE1P which is the high-energy phosphoenzyme formed from ATP with Na is also the Na -occluded E1 state it is suggested that the Na -occluded E1 state increases the affinity of the phosphoenzyme from pNPP for K through the interaction between a .

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