Chap 10. Conformational Change, Allosteric Regulation, Motors, and Work Conformation changed for controlling the activity of regulatory proteins for interconverting.

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Presentation transcript:

Chap 10. Conformational Change, Allosteric Regulation, Motors, and Work Conformation changed for controlling the activity of regulatory proteins for interconverting mechanical work and physicochemical free energy The coupling of conformation change and chemical reaction pumping ligands against chemical gradients synthesizing ATP from chemical potentials

A. Positive Cooperativity Sigmoid curve The characteristic of the cooperative binding of ligands ex. oxygen binding to myoglobin Allosteric enzymes Example: hemoglobin Four polypeptide chain, a2/b2 Four successive binding constants Greater fourth oxygen binding constant (100-1000 fold)

allosteric effectors: inhibitor or activator that that is generally different from the substrate and binds to its own site away from the active site homotropic effectors: interactions between identical substrate molecules that affect affinities heterotropic effectors: interactions between allosteric effectors and substrate that affect substrate affinities

B. Mechanisms of Allosteric Interactions and Cooperativity Deoxyhemoglobin and oxyhemoglobin Changes in quaternary structure: a units rotate relative to each other through 15 º Small tertiary structural changes

The Models of Cooperative Interaction The Monod-Wyman-Changeux (MWC) concerted mechanism The Koshland-Nemethy-Filmer (KNF) sequenctial model Eigen model Nested cooperativity

The Monod-Wyman-Changeux (MWC) Concerted Mechanism The simplest model Concerted, all or none, two-state Assumption The protein is an oligomer The protein exists in either of two conformational states, T and R, in equilibrium The T state has a lower affinity for ligands All binding sites in each state are equivalent and have identical binding constants

Koshland-Nemethy-Filmer sequential model (KNF) More accurate for some systems Assumption One conformation in the absence of ligands Conformational change upon binding. The change transmitted to neighboring vacant subunits Sites NOT SYMMETRIC

Eigen model: the General Model fully asymmetric the most complex difficult to work with