scholarly journals Effects of ethylenediaminetetra-acetate and deoxycholate on kinetic constants of the calcium ion-dependent adenosine triphosphatase of human erythrocyte membranes

1972 ◽  
Vol 130 (1) ◽  
pp. 311-314 ◽  
Author(s):  
H U Wolf
Keyword(s):  
Human Erythrocyte ◽  
Calcium Ion ◽  
Adenosine Triphosphatase ◽  
Kinetic Constants ◽  
Erythrocyte Membranes ◽  
Human Erythrocyte Membranes

scholarly journals Calcium ion-dependent p-nitrophenyl phosphate phosphatase activity and calcium ion-dependent adenosine triphosphatase activity from human erythrocyte membranes

1973 ◽  
Vol 136 (1) ◽  
pp. 185-194 ◽  
Author(s):  
Alcides F. Rega ◽  
Donaldo E. Richards ◽  
Patricio J. Garrahan
Keyword(s):  
Cell Membrane ◽  
Phosphatase Activity ◽  
Human Erythrocyte ◽  
Calcium Ion ◽  
Adenosine Triphosphatase ◽  
Erythrocyte Membranes ◽  
Dependent Atpase ◽  
Nitrophenyl Phosphate ◽  
Inner Surface ◽  
Human Erythrocyte Membranes

In the presence of ATP and of Mg2+, human erythrocyte membranes show a phosphatase activity towards p-nitrophenyl phosphate which is activated by low concentrations of Ca2+. The effect of Ca2+ is strongly enhanced if either K+ or Na+ is also present. Activation of the p-nitrophenyl phosphate phosphatase by Ca2+ reaches a half-maximum at about 8μm-Ca2+ and is apparent only when the ion has access to the inner surface of the cell membrane. Ca2+-dependent phosphatase activity can only be observed if ATP is at the inner surface of the cell membrane, and the presence of ATP seems to be absolutely necessary, since either its removal or its replacement by other nucleoside triphosphates abolishes the activating effect of Ca2+. The properties of the (ATP+Ca2+)-dependent phosphatase are very similar to those of the Ca2+-dependent ATPase (adenosine triphosphatase), also present in erythrocyte membranes, which probably is involved in Ca2+ transport in erythrocytes. The similarities suggest that both activities may be properties of the same molecular system. This view is further supported by the fact that p-nitrophenyl phosphate inhibits to a similar extent Ca2+-dependent ATPase activity and ATP-dependent Ca2+ extrusion from erythrocytes.

scholarly journals Activation of membrane-bound high-affinity calcium ion-sensitive adenosine triphosphatase of human erythrocytes by bivalent metal ions

1975 ◽  
Vol 147 (2) ◽  
pp. 359-361 ◽  
Author(s):  
H Pfleger ◽  
H U Wolf
Keyword(s):  
Metal Ions ◽  
Calcium Ion ◽  
Metal Ion ◽  
Adenosine Triphosphatase ◽  
Erythrocyte Membranes ◽  
Bivalent Metal ◽  
High Affinity ◽  
Human Erythrocyte Membranes ◽  
Bivalent Metal Ions ◽  
Membrane Bound

The Ca2+-sensitive ATPase (adenosine triphosphatase) of human erythrocyte membranes is activated, not only by Ca2+ ions, but also by a series of other bivalent metal ions including Sr2+, Ba2+, Mn2+, Ni2+, Co2+, Cd2+, Cu2+, Zn2+ and Pb2+. The degree of activation is dependent on the radius of the ion rather than on its nature, in contrast with the dissociation constant of the enzyme--metal ion complex.

scholarly journals Interaction of platelet plasma membranes with thrombin-activated platelets

Blood ◽  
1981 ◽  
Vol 57 (2) ◽  
pp. 305-312 ◽  
Author(s):  
HR Prasanna ◽  
HH Edwards ◽  
DR Phillips
Keyword(s):  
Human Erythrocyte ◽  
Plasma Membranes ◽  
Membrane Binding ◽  
Human Platelets ◽  
Platelet Membrane ◽  
Erythrocyte Membranes ◽  
Functional Sites ◽  
Activated Platelets ◽  
Platelet Membranes ◽  
Human Erythrocyte Membranes

Abstract This study described the binding of platelet plasma membranes to either control or thrombin-activated platelets. Glycoproteins in plasma membranes isolated from human platelets were labeled by oxidation with periodate followed by reduction with [3H]NaBH4. Labeled membranes were incubated with either control or thrombin-activated platelets. The amount of membranes bound was measured by separating platelets with bound membranes from solution by rapid centrifugation through 27% sucrose and determining the amount of radioactivity associated with platelets. Five- to sevenfold more membranes bound to thrombin- activated platelets than to control platelets. This enhanced binding of labeled membranes was completely inhibited by an excess of unlabeled platelet membranes. Human erythrocyte membranes had little affinity for either washed or thrombin-activated platelets and therefore did not compete for platelet-membrane binding. Binding of platelet membranes to thrombin-treated platelets was inhibited by prior incubation of the platelets with PGI2 suggesting that the enhanced binding of membranes was to activated platelets. This study demonstrates that the purified platelet membranes have functional sites that can mediate membrane binding to platelets and that quantitation of membrane binding appears to reflect the increased aggregation capability of activated platelets.

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