Lock-key model

In discussing the appearence of diastereoselectivity in natural systems, the rule of three-point contact is frequently used11). This rule implies that a prochiral substrate becomes a chiral one, when it is fixed on three nonidentical points on the enzyme system. On the other hand, the well-known lock-key model is mainly based on a specific spacial arrangement and does not take into account specific types of bonding to the matrix12). For a discussion of diastereoselectivity in reactions with metal complexes, it seems more appropriate to use such a lock-key model. 

Fig. 2. Principle mechanisms of formation of a receptor—substrate complex (a) Fischer s rigid "lock-and-key" model (b) "induced fit" model showing...

Living cells contain thousands of different kinds of catalysts, each of which is necessary to life. Many of these catalysts are proteins called enzymes, large molecules with a slotlike active site, where reaction takes place (Fig. 13.39). The substrate, the molecule on which the enzyme acts, fits into the slot as a key fits into a lock (Fig. 13.40). However, unlike an ordinary lock, a protein molecule distorts slightly as the substrate molecule approaches, and its ability to undergo the correct distortion also determines whether the key will fit. This refinement of the original lock-and-key model is known as the induced-fit mechanism of enzyme action. 

FIGURE 13.40 In the lock-and-key model of enzyme action, the correct substrate is recognized by its ability to fit into the active site like a key into a lock. In a refinement of this model, the enzyme changes its shape slightly as the key enters. 

Early in the last century, Emil Fischer compared the highly specific fit between enzymes and their substrates to that of a lock and its key. While the lock and key model accounted for the exquisite specificity of enzyme-substrate interactions, the imphed rigidity of the... 

Importantly, the internal diffusion model for lectins binding to mucins is distinct from the classical lock and key model of ligand binding to a receptor. The internal... 

The LOCK AND KEY model for enzyme specificity uses complementarity between the enzyme active site (the lock) and the substrate (the key). Simply, the substrate must fit correctly into the active site—it must be the right size and shape, have charges in the correct place, have the right hydrogen-bond donors and acceptors, and have just the right hydrophobic patches. 

What the induced-fit model is good at explaining is why bad substrates are bad, but like the lock and key model, it too fails to tell us exactly why good substrates are good. What is it about the proper arrangement that makes the chemistry fast ... 

Drugs are thought to bind to receptors in a lock-and-key model, meaning that the molecular shape of a drug determines how well, if at all, it will attach to a receptor and what activity it will have there. 

Two models currently exist to explain how an enzyme and its substrate interact. One model, called the lock and key model, suggests that an enzyme is like a lock, and its substrate is like a key. The shape of the active site on the enzyme exactly fits the shape of the substrate. A second model, called the induced fit model, suggests that the active site of an enzyme changes its shape to fit its substrate. Figure 6.21 shows both models. 

Diagram A shows the lock and key model of enzyme function. Diagram B shows the induced-fit model of enzyme function. 

Figure 8.1. Lock and key model (a) geometrical fit, (b) complementary pattern of functional groups, (c) site preference due to the solvent effect. The ligand L may better fit site A, but it binds preferentially to site B due to the solvent effect...

One of the earliest, simplest, and best-known examples of this concept is the lock-and-key model of enzyme action hrst proposed by German chemist Emil Fischer (1852-1919) in 1894. While it has been significantly modihed since that time, the general mode of action suggested by Fischer is probably generally correct for most types of enzyme action. According to the lock-and-key model, illustrated below. 

The topologically defined region(s) on an enzyme responsible for the binding of substrate(s), coenzymes, metal ions, and protons that directly participate in the chemical transformation catalyzed by an enzyme, ribo-zyme, or catalytic antibody. Active sites need not be part of the same protein subunit, and covalently bound intermediates may interact with several regions on different subunits of a multisubunit enzyme complex. See Lambda (A) Isomers of Metal Ion-Nucleotide Complexes Lock and Key Model of Enzyme Action Low-Barrier Hydrogen Bonds Role in Catalysis Yaga-Ozav /a Plot Yonetani-Theorell Plot Induced-Fit Model Allosteric Interaction... 

LINKED FUNCTIONS LOCK-AND-KEY MODEL OF ENZYME ACTION... 

Fe "-OOH (ES) complex, 43 95-97 heme-bound CO, 43 115 lock-and-key model, 43 106-107 mutation in proximal heme cavity, 43 98 residue location, 43 101-102 van der Waals surfaces, 43 112-113 Velcro model, 43 107 zinc-substituted, 43 110-111 plastocyanin, cross-linked, cyclic voltammogram, 36 357-358 promoters, 36 345-346 protein-electrode complex, 36 345, 347 redox potential, 36 349 self-exchange rate constants, 36 402 stability at electrode/electrolyle interface, 36 349-350... 

Liquid Crystals materials that have properties of both solids and liquids used extensively in digital displays Lithosphere outer surface of Earth including the crust and upper mantle Lock-and-Key Model model to explain how enzymes catalyze reactions with specific enzymes acting as locks that only certain substrates which act as keys can fit... 

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