. Biological structure and function; proceedings. Biochemistry; Cytology. COMPONENTS OF THE ENERGY-COUPLING MECHANISM 45 that the swelling and contraction are reflections of the action of " mechano- enzyme" systems similar to the actomyosin of muscle, in which inter- mediate enzymes of the energy-coupling mechanism may act as " mechano- enzymes" and undergo change of shape or charge distribution. If the ATP ADP exchange enzyme can exist in phosphorylated form, this might difi^er in configuration or in geometrical arrangement from the unphos- phorylated form and account for
. Biological structure and function; proceedings. Biochemistry; Cytology. COMPONENTS OF THE ENERGY-COUPLING MECHANISM 45 that the swelling and contraction are reflections of the action of " mechano- enzyme" systems similar to the actomyosin of muscle, in which inter- mediate enzymes of the energy-coupling mechanism may act as " mechano- enzymes" and undergo change of shape or charge distribution. If the ATP ADP exchange enzyme can exist in phosphorylated form, this might difi^er in configuration or in geometrical arrangement from the unphos- phorylated form and account for changes in the geometry or properties of the membrane [26, 34]. There is in fact a striking resemblance between the ATP-ase activity of the actomyosin system and that of the phosphory- lation mechanism. Mechanisms of membrane changes Y I Electron transport »- carrier~X Carrier ~X + P, < " carrier + P~X P~X + (E â(E) + X .P 'ADP ^. ADP ^=^ (!i'^=^ di' \- k ^ADP i ^ ATP â â mechanoproteins" n ATP + Membrane protein Protein phospho kinase. Fig. 6. Two possible mechanisms for alteration of membrane state through ATP-driven changes of shape or conformation of protein molecules. In the first, the mechano-enzyme may be an intermediate enzyme of energy coupling, such as \Ej whose shape may change as a function of binding of P or ADP or ATP. In the second, an independent membrane protein (possibly the "phosphoprotein" of mitochondria) may be activated by ATP to yield mechanical changes. Figure 6 indicates two possible ways in which contraction might be visualized. In the upper half is shown a representation in which an inter- mediate enzyme of the energy-coupling sequence is the "mechano- enzyme" activating the contractile changes. It is postulated to change shape or charge distribution when it is phosphorylated. On the other hand, it is possible that the contractile protein is not a member of the coupling sequence itself but perhaps is in equilibr
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