Mechanics and Energetics of Biological Transport

This book deals with energetics of transport processes, largely expressed in terms of the thermodynamics of irreversible pro­ cesses. Since at the present time too little is known about the molecular mechanism of transport, the present treatment is based largely on hypothetical models. Care has been taken, however, to define the crucial features of these models as generally as pos­ sible, so that the equations do not depend too much on hypotheti­ cal details. Accordingly, most equations, though developed on the basis of a mobile carrier (ferryboat) model, should apply equally to a conformational model, with an appropriate reinterpretation of the symbols. To better elucidate the essentials, the models are greatly simplified by special assumptions. Maximally, only two flows are assumed to be present in each model at one time: e. g. , two solute flows, the flow of solvent and of one solute, the flow of solvent and of heat. The simplifying assumptions may often be unreal. Hence the equations should not be applied un­ critically to actual mechanisms. They may at best serve as a ba­ sis on which the more appropriate equations may be developed. The book is not designed to give a complete kinetic analysis of the transport processes described. The kinetic equations are kept to the minimum required to describe the model concerned and to relate it to the corresponding thermodynamic equations. The in­ tention is to stress the close relationship between bioosmotic (transport) and biochemical processes in metabolism.

Contenu

1 Introduction.- 1.1 Chemical and Osmotic Processes - A Simple Model.- 1.2 Activities and (Electro) Chemical Potentials.- One-Flow Systems - Uncoupled Transport.- 2 Nonmediated (Free) Diffusion.- 2.1 Mechanistic Aspect.- 2.1.1 The Barrier.- 2.1.2 Diffusion Through Pores.- 2.1.3 Diffusion Through Lipid Layer.- 2.2 Treatment of Unmediated Diffusion in Terms of the Law of Mass Action (LMA).- 2.2.1 Diffusion Coefficient (Di).- 2.2.2 Permeability Coefficient (Pi).- 2.2.3 Unidirectional Fluxes - The Flux Ratio.- 2.2.4 Electric Driving Forces in Diffusion.- 3 Mediated ("Facilitated") Diffusion.- 3.1 Mechanistic Aspects of Mediation.- 3.1.1 General.- 3.1.2 Specificity.- 3.1.3 Translocation by Carriers.- 3.1.4 Translocation Through Channels.- 3.2 Treatment of Mediated Diffusion in Terms of the Law of Mass Action (LMA).- 3.2.1 General.- 3.2.2 Symmetric Carrier Systems.- 3.2.3 Asymmetric Carrier Systems.- 3.2.4 A Special System.- 3.2.5 Channel Systems.- 4 Isotope Interaction - Tracer Coupling.- 4.1 Mechanistic Aspects of Solute-Solute Interaction.- 4.1.1 General.- 4.1.2 Cis and Trans Effects.- 4.1.3 Coupling Phenomena.- 4.1.4 Effects on Flux Ratio.- 4.2 Treatment of Tracer Coupling (Isotope Interaction) in Terms of the Law of Mass Action (LMA).- 4.2.1 Friction.- 4.2.2 Association (Dimerization).- 4.2.3 Carrier Mediation.- 4.2.4 Solvent Drag.- 5 Energetics of One-Flow Systems. Treatment of One-Flow Systems in Terms of Thermodynamics of Irreversible Processes (TIP).- 5.1 Free Diffusion.- 5.2 Facilitated Diffusion.- 5.3 Tracer Coupling.- Two-Flow Systems - Energetic Coupling.- 6 Solute-Specific Coupling - Active Transport.- 6.1 Mechanistic Aspects of Coupling.- 6.1.1 Criteria and Definitions.- 6.1.2 Driving Forces.- 6.1.3 General Model of Active Transport.- 6.1.4 General Principles of Coupling.- 6.1.5 Scalar Coupling - The Source-and-Sink-Mechanism.- 6.1.6 Vectorial Coupling - The Conveyor Principle.- 6.2 Secondary Active Transport.- 6.2.1 Mechanism.- 6.2.2 Ion-Linked Cotransport (Symport).- 6.3 Primary Active Transport by Solute Translocation.- 6.3.1 General Mechanism.- 6.3.2 Ca2+-activated ATPase.- 6.3.3 Na+- K+-activated ATPase.- 6.4 Primary Active Transport by Group Translocation.- 6.4.1 General Mechanism.- 6.4.2 The Carnitin Cycle.- 6.4.3 The Redox Proton Pump.- 6.4.4 The Proton-Translocating ATPase.- 6.4.5 The Phosphotransferase.- 6.4.6 Glutamyl-Cycle.- 6.5 Treatment of Solute-Specific Coupling in Terms of the Law of Mass Action (LMA).- 6.5.1 General Procedure.- 6.5.2 Leakages.- 6.5.3 Secondary Active Transport.- 6.5.4 Primary Active Solute Translocation.- 6.5.5 Combined Push and Pull Effects.- 6.5.6 Group Translocation.- 7 Energetics of Coupled Transport Treatment of Active Transport in Terms of Thermodynamics of Irreversible Processes (TIP).- 7.1 The Basic Phenomenological Equations.- 7.1.1 General.- 7.1.2 Conventional Approach.- 7.1.3 Quasi-Chemical Notation.- 7.1.4 Leakages.- 7.1.5 Flux Ratio.- 7.2 Mechanistic Correlates of the Phenomenological Parameters.- 7.2.1 General.- 7.2.2 Secondary Active Transport.- 7.2.3 Primary Active Transport - Source-and-Sink Principle.- 7.2.4 Comparison Between LMA Treatment and TIP Treatment.- 7.3 Quantitative Evaluation of Coupling.- 7.3.1 Degree of Coupling.- 7.3.2 Efficiency of Coupling - Efficacy of Accumulation.- 7.3.3 Power of Transport Systems.- 7.4 Limitations of Thermodynamics of Irreversible Processes (TIP) Treatment.- 7.4.1 Proximity to Equilibrium.- 7.4.2 Other Quasi-Linear Ranges.- 8 Phase-Specific Forces.- 8.1 Drag Forces Between Solute and Solvent Flows.- 8.1.1 Mechanism.- 8.1.2 A Model.- 8.1.3 Treatment in Terms of TIP.- 8.2 Thermo-Osmotic Coupling.- 8.2.1 Mechanism.- 8.2.2 Treatment in Terms of TIP.- References.