Biochemical Devices Based on Enzymic Reactions

In an extensive study, Okamoto and co-workers [76-86] introduced a biochemical switching device based on a cyclic enzyme system in which two enzymes share two cofactors in a cyclic manner. Cyclic enzyme systems have been used as biochemical amplitiers to improve the sensitivity of enzymatic analysis [87-89], and subsequently, this technique was introduced into biosensors [90-93], In addition, cyclic enzyme systems were also widely employed in enzymic reactors, in cases where cofactor regeneration is required [94-107], Using computer simulations, Okamoto and associates [77,80-83] investigated the characteristics of the cyclic enzyme system as a switching device, and their main model characteristics and simulation results are detailed in Table 1.1, as is a similar cyclic enzyme system introduced by Hjelmfelt et al. [109,116], which can be used as a logic element. 

Subsequently, Okamoto and associates [84-86] investigated the connection of several cyclic enzyme systems in order to construct a network. In their models the cyclic enzyme system represents a biochemical neuron that participates in a biochemical neural network. These models are detailed in Table 1.2. Theoretical models of such networks were also proposed by Hjelmfelt and co-workers [109-111,116], and these are also presented in Table 1.2. 

Models for biochemical switches, logic gates, and information-processing devices that are also based on enzymic reactions but do not use the cyclic enzyme system were also introduced [76,115,117-122]. Examples of these models are presented in Table 1.3. It should also be mentioned that in other studies [108,112-114,116], models of chemical neurons and chemical neural networks based on nonenzymic chemical reactions were also introduced. 

I1J2 inputs to the system s substrate pools of Xi and X3, respectively. Simple mass action kinetics. Irreversible reactions. 

Same assumptions as in model 1 except Reaction mechanisms are assumed to be ordered bi-bi enzymic reactions. 

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