Enzyme switch

In step (3) the enzyme switches to its open conformation, and the unbroken DNA strand passes through the break in the first strand. 

For approximately 5% of the measured enzymes, a peculiar spontaneous inactivation pattern was observed (Fig. 25.2b and c). Rather than a one-step all-or-nothing inactivation or a continuous gradual decrease in activity, a transient phase was observed. During this phase, the enzyme switched between discrete active and inactive states. After each inactive period, only a fraction of the original activity was recovered until the enzyme was irreversibly deactivated. 

Density matters. The sedimenation value of aspartate tran scarbamoylase decreases when the enzyme switches to the R state. (Dn the basis of the allosteric properties of the enzyme, explain why the sedimentation value decreases. 

Phase plane analysis thus readily accounts for the main experimental observation on the control of glycolytic oscillations by the substrate injection rate. Below the lower critical value of the substrate injection rate v, a stable steady state is estabUshed, corresponding to a low level of reaction product and to an enzyme predominantly in the inactive T state. Above the higher critical value of v, the stable steady state is associated with a higher level of product and with an enzyme predominantly in the active state R. Sustained oscillations, in the course of which the enzyme switches back and forth between the R and T states, occur in the range delimited by the two critical values of the substrate input. 

FIGURE 9.15. Schematic representation of an enzyme switch responsive to penicillin based on penicillinase immobilized on a poly(pyrrole) film (see Ref. 97). On adding penicillin protons are produced, which cause a local decrease in the solution pH and hence an increase in the conductivity of the polymer. 

Bartlett, P.N., P.R. Birkin, and J.H. Wang. 1998. An enzyme switch employing direct electrochemical communication between horseradish peroxidase and a poly(amlme) film. Anal Chem 70 3685. 

FIGURE 12.16 (A) Enzyme switch responsive to glucose. The enzyme glucose oxidase is immobilized in a thin-... 

Matsue, T., M. Nishizawa, T. Sawaguchi, and T. Uchida. 1991. An enzyme switch sensitive to NADH. 7 Chem Soc Chem Commun 15 1029. 

Bartlett, P.N, and P.R. Birkin. 1993. Enzyme switch responsive to glucose. Anal Chem 65 1118. 

P. N. Bartlett, P. R. Birkin, J. H. Wand, F. Pabnisano, G. Benedetto, An Enzyme Switch Employing Direct Electrochemical Communication between Horseradish Peroxidase and a Poly(aniline) Film. Anal. Chem., 70 (1998) 3685—3694. 

Shimoboji, T., Larenas, E., Fowler, T., Kulkami, S., Hoffman, A. S., Stayton, P. S. (2002). Photoresponsive polymer-enzyme switches. Proceedings of the National Academy of Sciences, 99, 16592-16596. 

Immobilization of enzymes that induce local pH changes in the polymer is yet another approach to the fabrication of electroconductive polymer-based enzyme switches and/or sensors. The IDA electrode coated with... 

Shimoboji T, Larenas E, Fowler T, Kulkami S, Hoffinan AS, Staytrai PS (2002) Photoresponsive polymer-enzyme switches. PNAS 99 16592—16596... 

BattagUni F, Bartlett PN, Wang JH. Covalent attachment of osmium complexes to glucose oxidase and the application of the resulting modified enzyme in an enzyme switch responsive to glucose. Anal Chem 2000 72 502-509. 

Fig. 2 Scheme of enzyme-switch-regulated supramolecular hydrogel reproduced with permission from Ref. [16]... 

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