TY - JOUR
T1 - Mg2+-dependent, (Na+ + K+)-stimulated ATPase of human platelets. Properties and inhibition by ADP
AU - Moake, J. L.
AU - Ahmed, K.
AU - Bachur, N. R.
AU - Gutfreund, D. E.
PY - 1970/8/7
Y1 - 1970/8/7
N2 - The preparation and properties of a Mg2+-dependent, (Na+ + K+)-stimulated ATPase from platelets are described. The enzym system require Mg2+ for activity, is stimulated maximally by the presence of Na+ and K+ in a ratio of 11.5/1, has a pH optimum 7.30-7.40, and is half-maximally inhibited by ouabain at a concentration of 0.15 μM. The Km for ATP is approx. 0.4 mM. Enzyme activity is localized in both the "membrane" and "membrane-granule" subcellular fractions. Mg2+-dependent, (Na+ + K+)-stimulated ATPase activity is inhibited by ADP (which induces platelet aggregation) and by Pi. The inhibition by ADP is apparently not competitive with respect to ATP. Mg2+-dependent, K+-stimulated p-nitrophenyl phosphatase activity (a model for the externally-oriented K+-phosphatase portion of Mg2+-dependent, (Na+ + K+)-stimulated ATPase) is also inhibited by ADP. GDP, which does not induce aggregation of platelets, has no effect on the Mg2+-dependent, (Na+ + K+)-stimulated ATPase activity. It is postulated that ADP interacts with the external platelet membrane surface to inhibit Mg2+-dependent, (Na+ + K+)-stimulated ATPase activity with a resultant decrease in cation transport and membrane potential. This phenomenon may play a role in platelet aggregation.
AB - The preparation and properties of a Mg2+-dependent, (Na+ + K+)-stimulated ATPase from platelets are described. The enzym system require Mg2+ for activity, is stimulated maximally by the presence of Na+ and K+ in a ratio of 11.5/1, has a pH optimum 7.30-7.40, and is half-maximally inhibited by ouabain at a concentration of 0.15 μM. The Km for ATP is approx. 0.4 mM. Enzyme activity is localized in both the "membrane" and "membrane-granule" subcellular fractions. Mg2+-dependent, (Na+ + K+)-stimulated ATPase activity is inhibited by ADP (which induces platelet aggregation) and by Pi. The inhibition by ADP is apparently not competitive with respect to ATP. Mg2+-dependent, K+-stimulated p-nitrophenyl phosphatase activity (a model for the externally-oriented K+-phosphatase portion of Mg2+-dependent, (Na+ + K+)-stimulated ATPase) is also inhibited by ADP. GDP, which does not induce aggregation of platelets, has no effect on the Mg2+-dependent, (Na+ + K+)-stimulated ATPase activity. It is postulated that ADP interacts with the external platelet membrane surface to inhibit Mg2+-dependent, (Na+ + K+)-stimulated ATPase activity with a resultant decrease in cation transport and membrane potential. This phenomenon may play a role in platelet aggregation.
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U2 - 10.1016/0005-2736(70)90106-9
DO - 10.1016/0005-2736(70)90106-9
M3 - Article
AN - SCOPUS:4243875122
SN - 0005-2736
VL - 211
SP - 337
EP - 344
JO - BBA - Biomembranes
JF - BBA - Biomembranes
IS - 2
ER -