A vast number of biochemical reactions are catalyzed by molecules fixed to the surface of membranes (or other biological structures). Although trans-membrane processes have been extensively studied for the last 30 years, the focus on interfacial processes has lagged. The study of the mechanisms at these 'biointerfaces' is becoming increasingly important for the understanding of biological catalysts. This book is the first to deal with the physical and chemical principles of an emerging field of science, for which the authors have established the groundwork. While several specialized reviews have appeared on the various aspects of the subject, this text serves as a definitive primer; it puts this interdisciplinary field on a firm footing, develops key features of interfacial enzyme kinetics that include variables related to turnover processivity, and substrate accessibility and replenishment.

 

Key features:

• The first book in the field - concise, thorough and authoritative.

• The fundamentals developed in this book connect basic physical chemistry to biophysical chemistry, surface and colloid chemistry, enzymology, pharmacology, and cell biology.

• The key interfacial processes of turnover, processivity and replenishment are examined and it is shown how together they determine the catalytic efficiency of interfacial enzymes.

• Focuses on introducing a usable yet rigorous quantitative basis for analysis of interfacial catalysis in terms of the primary rate and equilibrium constants.

• Describes the quantitative characterization of function and inhibition of interfacial enzymes under conditions relevant for evaluation of their pharmacological potential.

In addressing issues and concerns in a growing field that borders physical, biological and surface sciences, this book will be of interest to a broad spectrum of scientists in such diverse fields as biochemistry, biophysics, enzymology, biotechnology, biomaterial science (phospholipid interfaces), pharmacology, bioorganic chemistry and colloid and interface sciences. As well as providing an informative text for advanced undergraduate and postgraduate students, many researchers in industry will also benefit from this comprehensive treatise.

Preface.

Theory Boxes.

List of Symbols.

 

Structral Diversity of Nonpolar and Amphiphilic Solutes.

To Be or Not to Be in Water.

The Hydrophobic Effect.

Knotty Issues of Interfacial Enzymology.

Pathophysiology of Lipolytic Enzymes.

Secreted PLA2 (sPLA2) Prototype for Interfacial Enzymology.

Summary and Outlook: Towards the Paradign for Interfacial Enzymology.

 

Aggregates and Dispersions.

Organized Micellar Aggregates in Aqueous Dispersions.

Amphiphile Organization and the Monomer - Micelle Equilibrium and Exchange.

The Concentration Issues in the Monomer - Aggregate Equilibria.

Exchange of Amphiphiles between Organized Interfaces.

Dispersed Phases.

Choice of Interface for Study of an Interfacial Enzyme.

Summary: Interface Determines the Accessibility and Replenishment Rate.

 

Constrained Reaction Path for the Turnover in the Aqueous Phase.

Analysis of the Steady State Turnover Cycle in the Aqueous Phase.

Ascertaining the Reaction Path in the Aqueous Phase.

PAF-Acetylhydrolase Hydrolyzes the Monodisperse Substrate.

Equilibrium Partitioning and Binding to Aggregates.

Summary: The Equilibrium Dilemma.

 

Conceptualizing Interfacial Processivity.

The Fourfold Meaning of the Substrate Concentration.

Constraints for Defining the Variables for the Reaction Progress in the Scooting Mode.

Integrity of Vesicles during the Scooting Mode Reaction Progress.

Tests for the Scooting Mode reaction progress by PLA2.

Ensemble Behavior of the Binding of the Enzyme to Vesicles.

Summary: Ensemble Behavior in a Microscopically Heterogeneous Environment.

 

Michaelis - Menten Equation for the Turnover in the Interface.

Catalytic Parameters from the Integrated Processive Reaction Progress.

Additional Constraints for the Analysis of the Interfacial Turnover Events for PLA2.

Uses of the Primary Catalytic Parameters.

Catalytic Mechanism of PLA2.

The Quality-of-Interface Effect.

Apparent Interfacial Activation.

Hopping and the Fast Enzyme Exchange Limit.

Summary: Variations in the Processivity.

 

Binding of Ions to the Interface.

Equilibria for the Binding of the Enzyme to the Interface.

Effective Equilibrium Constants.

The Cofactor Binding Obligatory for the Substrate Binding.

Detailed Balance Conditions and Local Concentrations for Effective Ligand Binding.

Resolution of the Interfacial Constants for PLA2.

Detailed Balance Conditions for PLA2.

Summary: Primary Equilibrium Parameters for the Kinetic Path.

 

Interfacial Catalytic Cycle Turnover in the Quasi-Scooting Mode.

Sparingly Soluble Substrates.

Reaction Rate with the Partitioned Substrate.

Interfacial Turnover by Triglyceride Lipase.

Lid on tl-Lipase Active Site.

Interfacial Allostery for the Quality-of-Interface effects.

Motifs for Close Contact of Proteins with the Interface.

Summary: Multiple States of the Enzyme at the Interface.

 

Interfacial Catalytic Turnover in the Quasi-Scooting Mode.

The Apparent Rate Parameters for the Pig Pancreatic PLA2.

Ks Allosteric effects of the Interface.

Analysis of the Interfacila Anionic Charge Preference: kcatS.

The Structural Basis for the Anionic Interface preference.

Modeling the I-face of PLA2.

Site-Directed Mutagenesis to Discern Interactions Along the I-face.

Summary: Residues involved in Charge Compensation.

 

Specific Inhibitors.

Kinetic effects of Nonspecific Inhibitors.

Kinetic effects of the Interface-Based Competitive Inhibitors.

Influence of Cofactor on the Scooting Kinetics.

Effects of the Interface-Based Inhibitor on the Integrated Rate Equation in the Scooting Mode.

Partitioning of the Inhibitor and Substrate between the Interface and the Aqueous Phase.

Summary: Multiple Pathways for Reduction of the Observed Rate.

 

Effects of the Accumulated products in the Zwitterionic Bilayers.

Model for the Delay Due to the Product Accumulation during the Reaction Progress on Phosphatidylcholine Vesicles.

Effect of the Accumulated Products on the Delay in the Monolayer Reaction Progress.

Summary: Activation by the Anionic Charge Induced by the Product Accumulation.

 

The Exchange Limit.

Exchange-Limited Kinetics of PLA2 in Detergent-Dispersed Mixed Micelles of Long Chain Phospholipids.

Effect of Bile Salts on the Pancreatic PLA2 Catalyzed Hydrolosis of Phosphatidylochines.

Kinetic Concerns for Interfaces of the Dispersed Phase.

The Nonideality Factor.

Summary: Nonidealities for Replenishment and Binding.

 

Dissection of the Entropy Loss on Interface Binding.

Synergistic effects of the Interface on Enzyme-Substrate Binding, Local Concentration and Scaffolding.

Diffusion Times in 1D, 2D and 3D.

Rate Enhancement by Facilitated Diffusion in 2D.

Summary: Dimensionality effects on the Equilibrium and Diffusion.

 

Reference.

Index.