Lock-and key mechanism

Affinity Chromatography. This technique involves the use of a bioselective stationary phase placed in contact with the material to be purified, the ligate. Because of its rather selective interaction, sometimes called a lock-and-key mechanism, this method is more selective than other lc systems based on differential solubiHty. Affinity chromatography is sometimes called bioselective adsorption. 

The binding of a substrate to its active center was first postulated by E. Fisher in 1894 using the lock and key mechanism which states that the enzyme interacts with its substrate like a lock and a key, respectively, i.e. the substrate has a matching shape to fit into the active site. This theory assumed that the structure of the catalyst was completely rigid and could not explain why the macromolecule was able to catalyze reactions involving large substrates and not those with small ones, or why they could convert non natural compounds with different structural properties to the substrate. 

Competition between liquid mobile phase and solid adsorbent 1 Competition between liquid mobile phase and liquid stationary phase 1 Molecular sieving 1 Lock and Key mechanism 1 Competition between liquid mobile phase and ionic stationary phase... 

Affinity chromatography is based on the lock-and-key mechanism prevalent in biological systems. The retention mechanism is very specific, but the technique is more time-consuming and more expensive than those employing other retention mechanisms. 

Mechanistically, an enzyme will bind the reactant, called the substrate, at a very specific site on the enzyme known as the active site. This resulting enzyme-substrate complex (ES), described as a lock-and-key mechanism, involves weak binding and often some structural changes—known as induced fit—that assist in stabilizing the transition state. In the unique microenvironment of the active site, substrate can rapidly be converted to product resulting in an enzyme=product (EP) complex that then dissociates to release product. 

Registration Using the Lock-and-key Mechanism in Soft Imprinting... 

Soft imprinting using flexible stamp has ample potential to be applied for reel-to-reel process [54, 55]. To achieve fast process in reel-to-reel device fabrication, passive alignment process between flexible stamp and substrate is needed rather than active optical alignment procedure. As a passive alignment process, lock and key mechanism was studied between flexible stamp and substrate in soft imprinting. 

Fig. 10.33. Registered PDMS/Mylar stamp on Substrate using lock and key mechanism A, B, C and D are optical microscope images of matched relief features of stamp on photoresist patterns of substrate a, b, c, and d are optical microscope images of matched keys of stamp on to locks on substrate.

The effect of enzymes was first described by Pasteur in his work on yeast fermentation. The term enzyme (from the Greek, to leaven) was first used by Kiihne [1] to describe reactions brought about by chemicals, rather than organisms, but it was Buchner who first used the suffix -ase to denote a biomolecule with enzymic activity when he named the chemical agent that promoted sugar fermentation zymase [2], The method by which enzymes could be so specific was coined the lock and key mechanism by Fischer as discussed in Chapter 1. He proposed that the substrate... 

Xanthan-locust bean gum gelation is a lock-and-key mechanism that guar gum does not fit (Rocks, 1971). Brownsey et al. (1988) came upon evidence of the denaturation (disorder-order transition) of the xanthan helix, and of binding of the stereochemically compatible cellulose chains. Having studied a series of stereochemically compatible synergistic and non-synergistic blends of xanthan and other gums, Morris (1992) concluded that denaturation of the xanthan helix was necessary. 

In Class II aaRSs, the bound ATP molecule interacts with motifs 2 and 3 (Fig. 2). The fS- and y-phosphates bend toward the adenine ring and are stabilized by three Mg + ions. The ribose of the ATP molecule adopts a 3 -endo conformation, as opposed to the 2 -endo conformation in Class I aaRSs. The amino acid side chain tends to bind by a lock-and-key mechanism, whereas its backbone interacts via an induced fit. Similar to Class I... 

Different theories have been proposed on how enzymes bind their specific substrates and achieve these huge rate accelerations [1]. One key question that remains to be answered is how dynamic effects contribute to the activity and specificity of enzymes. The initially proposed lock and key mechanism was supported by the large number of X-ray structures, which represent static snapshots of one enzyme conformation. Along this line, the observation of... 

The induced-fit mechanism is a more realistic version of the lock and key mechanism, which assumes that the substrate and enzyme fit together like a lock and key. 

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