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Structural Biochemistry/Protein function/Lock and Key

In the Lock and Key Model, first presented by Emil Fisher, the lock represents an enzyme and the key represents a substrate. It is assumed that both the enzyme and substrate have fixed conformations that lead to an easy fit. Because the enzyme and the substrate are at a close distance with weak attraction, the substrate must need a matching shape and fit to join together. At the active sites, the enzyme has a specific geometric shape and orientation that a complementary substrate fits into perfectly. The theory behind the Lock and Key model involves the complementarity between the shapes of the enzyme and the substrate. Their complementary shapes make them fit perfectly into each other like a lock and a key. According to this theory, the enzyme and substrate shape do not influence each other because they are already in a predetermined perfectly complementary shape. As a result, the substrate will be stabilized. This theory was replaced by the induced fit model which takes into account the flexibility of enzymes and the influence the substrate has on the shape of the enzyme in order to form a good fit.

The active site is the binding site for catalytic and inhibition reaction of the enzyme and the substrate; structure of active site and its chemical characteristic are of specificity for binding of substrate and enzyme. Three models of enzyme-substrate binding are the lock-and-key model, the induced fit model, and the transition-state model. The lock-and-key model assumes that active site of enzyme is good fit for substrate that does not require change of structure of enzyme after enzyme binds substrate.

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Lock-and-key model

strong>Lock-and-key model n., [lɑk ænd ki ˈmɑdl̩] Definition: a model for enzyme-substrate interaction

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Lock-and-key model Definition

Lock-and-key model is a model for enzyme-substrate interaction suggesting that the enzyme and the substrate possess specific complementary geometric shapes that fit exactly into one another. In this model, enzymes are depicted as highly specific. They must bind to specific substrates before they catalyze chemical reactions . The term is a pivotal concept in enzymology to elucidate the intricate interaction between enzymes and substrates at the molecular level. In the lock-and-key model, the enzyme-substrate interaction suggests that the enzyme and the substrate possess specific complementary geometric shapes that fit exactly into one another. Like a key  into a  lock , only the correct size and shape of the substrate ( the key ) would fit into the  active site  ( the keyhole ) of the enzyme ( the lock ).

Compare: Induced fit model   See also: enzyme , active site , substrate

Lock-and-key vs. Induced Fit Model

At present, two models attempt to explain enzyme-substrate specificity; one of which is the lock-and-key model , and the other is the Induced fit model . The lock and key model theory was first postulated by  Emil Fischer   in 1894. The lock-and-key enzyme action proposes the high specificity of enzymes. However, it does not explain the stabilization of the transition state that the enzymes achieve. The induced fit model (proposed by Daniel Koshland in 1958) suggests that the active site continues to change until the substrate is completely bound to the active site of the enzyme, at which point the final shape and charge are determined. Unlike the lock-and-key model, the induced fit model shows that enzymes are rather flexible structures. Nevertheless, Fischer’s Lock and Key theory laid an important foundation for subsequent research, such as during the refinement of the enzyme-substrate complex mechanism, as ascribed in the induced fit model. The lock-and-key hypothesis has opened ideas where enzyme action is not merely catalytic but incorporates a rather complex process in how they interact with the correct substrates with precision.

Key Components

Components of the lock and key model:

• Enzyme : the enzyme structure is a three-dimensional protein configuration, with an active site from where the substrate binds.
• Substrate : often an organic molecule, a substrate possesses a structural feature that complements the geometry of the enzyme’s active site.

In the lock and key model, both the enzymes and the substrates facilitate the formation of a complex that lowers the activation energy needed for a chemical transformation to occur. Such reduction in the activation energy allows the chemical reaction to proceed at a relatively faster rate, making enzymes crucial in various biological and molecular processes.

Lock-and-key Model Examples

Some of the common examples that are often discussed in the context of the Lock and Key Model are as follows:

• Enzyme lactate dehydrogenase with a specific active site for its substrates, pyruvate and lactate. The complex facilitates the interconversion of pyruvate and lactate during anaerobic respiration
• Enzyme carbonic anhydrase with a specific active site for the substrates carbon dioxide and water. The complex facilitates the hydration of carbon dioxide, forming bicarbonate
• Enzyme lysozyme binding with a bacterial cell wall peptidoglycan, which is a vital immune function

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• Aryal, S. and Karki, P. (2023).  “Lock and Key Model- Mode of Action of Enzymes”. Microbenotes.com. https://microbenotes.com/lock-and-key-model-mode-of-action-of-enzymes/
• Farhana, A., & Lappin, S. L. (2023, May).  Biochemistry, Lactate Dehydrogenase . Nih.gov; StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK557536/

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Qualitative and quantitative analyses of a ‘lock and key’ hypothesis of depression

1998, Psychological Medicine

Background. We examine a ‘lock and key’ (‘L–K’) hypothesis to depression which posits that early adverse experiences establish locks that are activated by keys mirroring the earlier adverse experience to induce depression.Methods. Two-hundred and seventy clinically depressed patients were examined with open-ended and pre-coded interview questions to ascertain both early adverse experiences and precipitating life events. Qualitative and quantitative data analyses examined for any associations between developmental ‘locks’ and precipitating ‘keys’.Results. Qualitative assessment suggested ‘L–K’ links in almost one-third of the sample, and examples are provided. While quantitative analyses indicated significant associations between several identical ‘lock’ and ‘key’ constructs, evidence of specificity was rare. When individual ‘locks’ and ‘keys’ were consolidated into three higher-order constructs, variable models were suggested, including a non-specific link, a specific link and absen...

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Comparison of Lock Chamber Calculation Methods

• Published: 29 November 2018
• Volume 52 , pages 418–424, ( 2018 )

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• S. N. Levachev 1 ,
• A. G. Gogin 1 &
• A. M. Shaitanov 1  

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Two methodologies for navigable lock chamber calculation are analyzed. Preliminary calculation was performed using the finite element model and Construction Specifications (CS) techniques. The feasibility of calculation using the finite element model was assessed and compared with manual calculation; the advantages and shortcomings of the techniques under consideration were manifested. Conclusions on the expediency of applying this method of lock chamber calculation of a dock design have been reached.

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Translated from Gidrotekhnicheskoe Stroitel’stvo , No. 6, June 2018, pp. 32 – 39.

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Levachev, S.N., Gogin, A.G. & Shaitanov, A.M. Comparison of Lock Chamber Calculation Methods. Power Technol Eng 52 , 418–424 (2018). https://doi.org/10.1007/s10749-018-0968-3

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Published : 29 November 2018

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DOI : https://doi.org/10.1007/s10749-018-0968-3

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