Mechanism of Free Energy Coupling in Active Transport

Target Molecular Size of the Red Beet Plasma Membrane ATPase

“…An oligomeric structure for linking ATP hydrolysis to transport, however, would be consistent with the proposal by Boyer et al (2) for the requirement of dual catalytic sites acting out of phase with one another. Such models have been proposed for the Na, K-ATPase (14), SR CaATPase (29), and the gastric H, K-ATPase (10). Therefore, these types of proposals for a structure-function relationship in these well characterized transport ATPases isolated from animal cells may be relevant to the higher plant plasma membrane ATPase and may represent a perspective for further study.…”

The rate‐limiting step and nonhyperbolic kinetics in the oxidation of ferrocytochrome c catalyzed by cytochrome c oxidase

“…It does not seem to be generally appreciated that such kinetics is also displayed by enzymes with a single substrate-binding site, if this site has different affinities in two states of the protein linked by a slow transition [22]. The existence of such states is an obligatory part of any pump mechanism [20,23], 4 and one would ~onsequentiy expect the kinetics of the driving reaction to be nonhyperbolic. Such kinetics has indeed been observed with ATP-driven pumps [ 11,24,25].…”

The catalytic cycle of P‐glycoprotein

“…Pgp differs from other transport ATPases in that it shows no high-affinity binding site tbr Mg-ATP, nor does it utilize a covalent E-P catalytic intermediate. Changes in free energy associated with such species during the catalytic cycle are thought to be coupled to conformational changes at transport substrate binding sites in other transport ATPases [42]. In Pgp, P, binding occurs with relatively weak affinity (above), implying that a large lYee energy change occurs during catalysis before the stage of Pi release.…”