| AAPPS Bulletin Vol.13 No.2 April 2003 |
Articles
Catalytic Wheel, Brownian Motor, and Biological Energy Transduction(PDF,1.1MB)
Tian Yow Tsong,National Taiwan University, Taiwan
Cheng-Hung Chang,National Center for Theoretical Sciences, Taiwan
abstract---
An enzyme turns over, or recycles during each catalytic process. It is a catalytic wheel, analogous to a motor, or an engine. The fuel, or the driving force for the wheel, is the free energy of the substrate (S) to product (P) conversion (ΔGR), or a free energy output of a coupled chemical reaction. When ΔGR of the S → P reaction is negative the reaction is spontaneous and the downhill wheel motion requires no external input of energy. When ΔGR is positive the wheel must turn uphill against a workload, a reaction that produces energy must be coupled to the wheel. The synthesis of ATP from ADP and Pi in a cell is an uphill reaction and the energy required for the synthesis is derived from the dissipation of a proton gradient, or an electric potential. This article focuses on mechanisms of action of the uphill catalytic wheels. It is shown that the coupling of an external energy source to an uphill catalytic wheel can be done, with nearly 100% efficiency, by mechanisms of the Brownian Motor. Theory of electroconformational coupling (TEC) is used to construct a Brownian motor, and electric activation of an ion pump, Na, K-ATPase is used to demonstrate its basic principles. A TEC Motor has three essential elements: 1) the ability of the protein to interact with an electric field, 2) existence of at least two conformations of protein that oscillate or fluctuate on interaction with the applied field, and 3) a built-in asymmetry in the molecular interactions with substrate and product. It is shown that the TEC Motor is a generic model and applicable to other types of biological energy transducers. |
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