Reversible protein photoactivation

FIGURE 133.3 Reversible protein photoactivation. The attachment of azobenzene (a), cinnamate (b), or spiropyr-ane-merocyanine (c) to active sites in proteins enables reversible photomodulation of activity. These photoswitches involve reversible cis-trans isomerization (a-c) and cyclization (c) reactions. 

For systems that are naturally and reversibly photosensitive such as the carbon monoxide complexes of heme proteins [18,. 30, 31], initiation by a light pulse is possible. By preparation of inert but photoactivable reactant or cofactor precursors such as caged ATP [32-34], photosensitivity may be conferred on otherwise photoinert systems [21], thus extending the generality of this approach. This approach was first combined with x-ray monitoring by Blasie [35, 36], in studies of oriented multilayers containing the Ca2+-ATPase from sarcoplasmic reticulum. 

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