Enzyme Mechanistic Action Summarized

Fischer l suggested at the end of the 19th century that unique activity of enzymes is related to the need for reactant molecules to fit optimally in the enzyme cavity. This is the lock and key molecular recognition model. Later Koshlandl l postulated the concept of induced fit the enzymes assume shapes that are complementary to that of the substrate after the substrate is bound. 

Paulingl l suggested in 1948 a strategy for developing enzyme cavities that stabilize the transition state of the rate-limiting step. This can be recognized as the need for a substrate to have an optimum interaction with the enzyme. We have seen that the stabihzation of pretransition-state structures is usually the essential step that stabilizes transition states. 

Liktenstein, New Trends in Enzyme Catalysis and Biomimetic Chemical Reactions, Kluwer, Dordrecht (2003)  

Kimura, T. Koike, in Bioinorganic Catalysis, J. Reedijk, E. Bouwman (eds.), 

Shilov, Metal Complexes in Biomimetic Chemical Reactions, CRC Press, Boca Raton, 1997  

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Mechanistic aspects of the action of tyrosinase and the usual transduction schemes have been summarized on several occasions [166,170-173]. In short, this copper enzyme possesses two activities, mono- and di-phenolase. Due to the predominant presence of the mono phenolase inactive form (met-form), the enzyme is inherently inefficient for the catalysis of these monophenol derivatives. However, in the presence of a diphenol, the catalytic cycle is activated to produce quinones and the scheme results in an efficient biorecognition cascade. This activation is achieved more efficiently when combined with electrochemical detection through the reduction of the produced quinones [166], as illustrated in Fig. 10.5. Consequently, a change in the rate-hmiting step can be observed through kinetic to diffusion controlled sensors with a concomitant increase in stability and sensitivity, as depicted in Fig. 10.6. 

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