PMID: 148293May 4, 1978

Reversible shift between two states of Ca2+-ATPase in human erythrocytes mediated by Ca2+ and a membrane-bound activator

Biochimica Et Biophysica Acta
O Scharff, B Foder


The (Ca2+ + Mg2+)-dependent ATPase (ATP phosphohydrolase, EC from human erythrocytes occurred in two different states, A-state and B-state, depending on the membrane preparation. The A-state showed low maximum activity (V) and the Ca2+ activation was characterized by a Hill coefficient, nH, of about 1 and a Michaelis constant, KCa, about 30 micron. The B-state showed high V, a nH above 1, which indicates positive cooperativity of Ca2+ activation, and KCa of about 1 micron. With varying ATP concentrations, both the A-state and B-state showed negative cooperativity and slightly different values of Km. The B-state was shifted to A-state when the membranes were exposed to low Ca2+ concentration. The shift reached 50% at approx. 0.5 micron Ca2+. At the low Ca2+ concentrations an activator was released from the membranes. The A-state was shifted to the B-state when the membranes were exposed to Ca2+ in the presence of the activator. The shift reached 50% at about 30 micron Ca2+. The recovery of high V was time dependent and lasted several minutes. Increasing concentrations of Ca2+ and activator accelerated the recovery. It is suggested that the A-state and the B-state correspond to enzyme free of activator and enzyme associa...Continue Reading


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Related Concepts

Ca(2+)-Transporting ATPase
Tissue Membrane
Adenosine Triphosphatases
Calcium Pump Activity
Specimen Type - Erythrocytes
Red Blood Cell Count Measurement
DNA-dependent ATPase
Interphase Cell

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