Figure 15-11. Model of the mechanism of action of muscle Ca2+ ATPase, which is located in the sarcoplasmic reticulum (SR) membrane.

Figure 15-11Model of the mechanism of action of muscle Ca2+ ATPase, which is located in the sarcoplasmic reticulum (SR) membrane

Only one of the two α subunits of this P-class pump is depicted. E1 and E2 are alternate conformational forms of the protein in which the Ca2+-binding sites are on the cytosolic and exoplasmic faces, respectively. An ordered sequence of steps, as diagrammed here, is essential for coupling ATP hydrolysis and the transport of Ca2+ ions (red circles) across the membrane. ~P indicates a high-energy acyl phosphate bond;  — P indicates a low-energy phosphoester bond. See the text for more details. [Adapted from W. P. Jencks, 1980, Adv. Enzymol. 51:75; W. P. Jencks, 1989, J. Biol. Chem. 264:18855; and P. Zhang et al., 1998, Nature 392:835.]

From: Section 15.5, Active Transport by ATP-Powered Pumps

Cover of Molecular Cell Biology
Molecular Cell Biology. 4th edition.
Lodish H, Berk A, Zipursky SL, et al.
New York: W. H. Freeman; 2000.
Copyright © 2000, W. H. Freeman and Company.

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