Conformation changing effect

When the enzyme molecule is close to the substrate molecule, due to the interactions between each other, both the enzyme molecule and substrate molecule could have conformation changes. Thus it is more beneficial to combine with substrate and react, and increase the reaction velocity greatly. 

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Comprehensive laser flash photolysis stndies on chicken and human SO have probed the rates of intermolecular electron transfer (lET, see Intermolecular) between the Mo and heme centers. Data are consistent with a CEPT mechanism interconverting Fe V[Mo02] " and Fe /[MoO(OH)]+ centers. To account for the wide range of lET rates (20-1400 s ), it has been proposed that protein conformational changes effectively gate lET by changing the Fe- Mo distance. 

A. Krzyzaniak, P. Salanski, J. Jurczak, J. Barciszewski, B-Z DNA reversible conformation changes effected by high pressure, FEBS Lett. 279 (1991) 1. ... 

A prototype of such phenomena can be seen in even the simplest carboxylic acid, acetic acid (CH3CHOOH). Acidity is determined by the energy or free energy difference between the dissociated and nondissociated forms, whose energetics usually depend significantly on their conformation, e.g., the syn/anti conformational change of the carboxyl-ate group in the compound substantially affects the acid-base equilibrium. The coupled conformation and solvent effects on acidity is treated in Ref. 20. 

Up to this point, we have emphasized the stereochemical properties of molecules as objects, without concern for processes which affect the molecular shape. The term dynamic stereochemistry applies to die topology of processes which effect a structural change. The cases that are most important in organic chemistry are chemical reactions, conformational changes, and noncovalent complex formation. In order to understand the stereochemical aspects of a dynamic process, it is essential not only that the stereochemical relationship between starting and product states be established, but also that the spatial features of proposed intermediates and transition states must account for the observed stereochemical transformations. 

The working hypothesis is that, by some means, interaction of an allosteric enzyme with effectors alters the distribution of conformational possibilities or subunit interactions available to the enzyme. That is, the regulatory effects exerted on the enzyme s activity are achieved by conformational changes occurring in the protein when effector metabolites bind. 

The hormonal stimulation of adenylyl cyclase is effected by a transmembrane signaling pathway consisting of three components, all membrane-associated. Binding of hormone to the external surface of a hormone receptor causes a conformational change in this transmembrane protein, which in turn stimulates a GTP-binding protein (abbreviated G protein). G proteins are heterotrimeric proteins consisting of a- (45-47 kD), /3- (35 kD), and y- (7-9 kD) subunits. The a-subunit binds GDP or GTP and has an intrinsic, slow... 

So how do the foot structures effect the release of Ca from the terminal cisternae of the SR The feet that join the t-tubules and the terminal cis-ternae of the SR are approximately 16 nm thick. The feet apparently function by first sensing either a voltage-dependent conformation change (skeletal mus-... 

One interesting phenomenon was the effect of the boron substituent on enantioselectivity. The stereochemistry of the reaction of a-substituted a,/ -unsatu-rated aldehydes was completely independent of the steric features of the boron substituents, probably because of a preference for the s-trans conformation in the transition state in all cases. On the other hand, the stereochemistry of the reaction of cyclopentadiene with a-unsubstituted a,/ -unsaturated aldehydes was dramatically reversed on altering the structure of the boron substituents, because the stable conformation changed from s-cis to s-trans, resulting in production of the opposite enantiomer. It should be noted that selective cycloadditions of a-unsubsti-tuted a,/ -unsaturated aldehydes are rarer than those of a-substituted a,/ -unsatu-... 

A basic concept in receptor pharmacology is the idea of orthosteric and allosteric interaction. Orthosteric interaction occurs when two molecules compete for a single binding domain on the receptor. With allosteric interactions two molecules each have their own binding domain on the receptor and the two interact through effects on the protein (conformational change). Tims, with orthosteric interactions only one molecule may occupy the receptor at any one instant whereas with allosteric interactions both molecules can bind to the receptor at the same time. There are implications for... 

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