Chemical transduction

Biosensors will thus include a recognition element of biological nature, that allows the selective recognition of the analyte in the course of a biochemical reaction (chemical transduction), and an energy transducer (stemming from the latin word transducere, to lead across) that transforms... 

Enzymes can be used not only for the determination of substrates but also for the analysis of enzyme inhibitors. In this type of sensors the response of the detectable species will decrease in the presence of the analyte. The inhibitor may affect the vmax or KM values. Competitive inhibitors, which bind to the same active site than the substrate, will increase the KM value, reflected by a change on the slope of the Lineweaver-Burke plot but will not change vmax. Non-competitive inhibitors, i.e. those that bind to another site of the protein, do not affect KM but produce a decrease in vmax. For instance, the acetylcholinesterase enzyme is inhibited by carbamate and organophosphate pesticides and has been widely used for the development of optical fiber sensors for these compounds based on different chemical transduction schemes (hydrolysis of a colored substrate, pH changes). 

Osteocytes are formed by the incorporation of osteoblasts into bone matrix. They remain in contact with other osteocytes via gap junction-coupled cell processes that form small channels through the matrix, the canaliculi. These small channels connect the cell body containing lacunae with each other and ECM external to the bone and play an important role in mechano-chemical transduction. 

New methods have been developed for the construction of artificial enzymes. A general method for obtaining new substrate-specific catalytic proteins is to develop antibodies towards transition states of the reaction in question by using molecules as antigens which simulate the transition state [33]. Although these catalytic antibodies would have the disadvantages implied for protein molecules, the host molecules mentioned before [41] and specifically functionalized host molecules [45] would imply the properties of a catalyst and hence be potentially suitable for chemical transduction in a sensor. 

Thompson, M., Dorn, W. H., Selective Chemical Transduction Based on Chemoreceptive Control of Membrane Ion Permeability, in Chemical Sensors, Edmonds, T. E. (ed.) Glasgow Blackie and Sons, 1988, pp. 168-190. 

Change in the Hydrophobicity (Extent of Oil-like Character) Due to Action on One Functional Group, for Example, Reduction of Oxidized N-methyl Nicotinamide, Moves the Transition Zone for a Second Functional Group, for Example, the Carboxyl/Carboxylate Chemical Couple Electro Chemical Transduction... 

Figure 5.21. Photo-mechanical and photo-chemical transduction in a model protein that contains a proto-natable glutamic acid residue and a chromophore capable of being driven from trans to cis on absorption of 300 nm light, both existing within the same hydrophobic association domain. (A) Ultraviolet absorption spectra showing the changes in the spectrum on going from 100% trans to 90% cis on illumination with 300 nm light. (B) Light-driven shift of isomer from trans to cis increases the value of T,. (C) Light-driven shift of isomer from trans to cis lowers the pKa of Glu carboxy-late. (From Heimbach. ...

Electro chemical transduction Electro thermal transduction... 

Baro thermal transduction Baro <- chemical transduction... 

Mechano Chemical Transduction (Stretch-Induced Proton Uptake)... 

Figure 5.23. Mechano-chemical transduction exhibited by carboxyl-containing cross-linked elastic model protein (A) Stretch gives nonlinear increases in pKa values despite the linear stress-strain curve...

D.W. Urry, L.C. Hayes, D.C. Gowda, S.-Q. Peng, and N. Jing, Electro-chemical Transduction in Elastic Protein-based Polymers. Biochem. Biophys. Res. Commun., 210,1031-1039,1995. 

Experimental Data on Electro-chemical Transduction Efficiency... 

In relation to the hydrophobic consilient mechanism, it is relevant to note that the redox centers are positively charged metal ions that become less charged on the addition of the electron and more charged on oxidation. In general, the effect of reduction of the redox sites, for example, heme iron and copper centers, is to increase hydrophobicity. Because a change in the redox state results in proton translocation, the protein-based machine. Complex IV, performs electro-chemical transduction. 

Coherence of Phenomena for Electro-chemical Transduction Demonstrated in Designed Elastic-contractile Model Protein and the Redox Bohr Effect in Complex IV... 

Both protein machines of ATP synthase are rotary motors, made possible by the mechanical coupling of chemo-mechanical transduction due to the Fo-motor to mechano-chemical transduction of the Fi-motor. A single rotor driven by the membranous Fo-motor in turn drives the extramembranous Fj-motor. The Fo-motor of yeast mitochondria, for example, exhibits a 10-fold rotational symmetry, providing a 10-step rotary engine, whereas the Fi-motor of all ATP synthases exhibits a threefold rotational symmetry, resulting in a threefold rotary engine. 

The rotor that is driven by the Fo-motor comprises a single y-subunit and a small e-subunit attached to the y-subunit at a point proximal to the base of the Fo-motor. This is called the y-rotor. In the hydrophobic elastic consilient mechanism, the interactions of a hydrophobi-cally asymmetric y-rotor with the housing of the Fi-motor with different occupancy states of the catalytic sites constitute the basis for mechano-chemical transduction of the Fi-motor. 

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