title: Pre-steady state kinetics of ATP hydrolysis by Na,K-ATPase.
abstract: Fast reaction kinetics of ATP hydrolysis by Na,K-ATPase has been investigated by following absorption pattern of pH sensitive dye in stopped flow spectrophotometer. Distinct pre-steady state phase signal could be recorded with an initial decrease in acidity followed by increase in acidity. Average half time for H(+) absorption and peak alkalinity was, respectively, 30 ms and 60 ms. Under optimal Na(+) (120 mM) and K(+) (30 mM) concentrations, magnitude of both H(+) absorption and H(+) release are found to be about 1.0 H(+)/ATPase molecule. H(+) absorption and release decreased with decrease in Na(+) concentration, H(+) release was more affected. Both H(+) absorption and H(+) release are found to be independent of K(+) concentration in the pre-steady state phase. No H(+) absorption or release was observed following mixing of either ADP, Na(+) or K(+) alone with ATPase. Effect of delayed mixing of Na(+) or K(+) on two phases of pre-steady state cycle indicates that ATP hydrolytic cycle starts without K(+) ions if optimal Na(+) is present. ATP hydrolytic cycle does not start in the absence of Na(+) ions. Results obtained have been interpreted in terms of an extended kinetic scheme for Na,K-ATPase.
authors.affiliation: Department of Biosciences, Jamia Millia Islamia, New Delhi, India.
authors.forename: Nikhat
authors.initials: N
authors.lastname: Manzoor
authors.forename: Mohammad M
authors.initials: MM
authors.lastname: Haque
authors.forename: Luqman A
authors.initials: LA
authors.lastname: Khan
mesh_terms: D000042:Absorption; D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D006041:Goats / Q000378:metabolism*; D006868:Hydrolysis; D007700:Kinetics; D011188:Potassium / Q000378:metabolism; D011522:Protons; D011732:Pyridoxal Phosphate / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013997:Time Factors
chemical_list: D011522:Protons; D011732:Pyridoxal Phosphate; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium