Photomodulated Azoaldolase: A Model for Light Intervention in Biological Systems?

Abstract

Azoaldolase is obtained from rabbit muscle aldolase by adding an azo chromophore to a cysteine side chain in each of the four enzyme subunits. The enzyme becomes photosensitive whereas both its catalytic activity and the michaelian kinetics are retained. Chromophore excitation causes E to Z isomerization of the azo bond, and mutually influences the protein-substrate equilibria. The various isomerization and substrate binding equilibria have been investigated under the hypothesis of a cyclic process described by four linked equilibrium constants. The mechanism of the light effect is a continuous adaptation of the specific parameters of the active protein, that is substrate recognition and rate of the catalyzed process. Absorbed light allows the rapid modification of the concentrations of various related molecules, depending on the used frequencies. At present such a mechanism has not been described in photobiology; so azoaldolase can be taken as a model for a possible new mechanism of light regulation of a biological system, based on changes in the molecular recognition by an active protein against its substrate.

Cis−Trans Isomerization of Organic Molecules and Biomolecules: Implications and Applications

“…Moreover, this photoresponsive azoaldolase can be considered as a model for a possible mechanism of light regulation in biological systems, based on variations in the molecular recognition of the substrate by the active protein. 339 Functional photoswitchable horseradish peroxidase mutants containing a p-phenylazophenylalanine residue at varying positions have also been described. 340…”

“…In a recent report, the design of a photosensitive azoaldolase demonstrated photomodulation of an enzyme without affecting its catalytic activity or its Michaelian kinetics. Moreover, this photoresponsive azoaldolase can be considered as a model for a possible mechanism of light regulation in biological systems, based on variations in the molecular recognition of the substrate by the active protein …”