Enzyme light-active

Molecular characteristics of luciferase. A molecule of the luciferase of G. polyedra comprises three homologous domains (Li et al., 1997 Li and Hastings, 1998). The full-length luciferase (135 kDa) and each of the individual domains are most active at pH 6.3, and they show very little activity at pH 8.0. Morishita et al. (2002) prepared a recombinant Pyrocystis lunula luciferase consisting of mainly the third domain. This recombinant enzyme catalyzed the light emission of luciferin (luminescence A.max 474 nm) and the enzyme was active at pH 8.0. The recombinant enzyme of the third domain of G. polyedra luciferase was crystallized and its X-ray structure was determined (Schultz et al., 2005). A -barrel pocket putatively for substrate binding and catalysis was identified in the structure, and... 

This strategy will likely he used to light-activate other enzymes of interest in living cells provided that enzymatic function is dependent on just one or a few residues of the protein. Another useful application could he the decaging of phosphorylated, ubiquitinated, or otherwise posttranslationally modified residues with light at specific time points for examination of signal transduction pathways. 

FIGURE 20-19 Light activation of several enzymes of the Calvin... 

Redox enzymes are the active component in many electrochemical enzyme electrode biosensor devices.1821 The integration of two different redox enzymes with an electrode support, in which one of the biocatalysts is photoswitchable between ON and OFF states, can establish a composite multisensor array. The biomaterial interface that includes the photoswitchable enzyme in the OFF state electrochemi-cally transduces the sensing event of the substrate corresponding to the nonphoto-switchable enzyme. Photochemical activation of the light-active enzyme leads to the full electrochemical response, corresponding to the analysis of the substrates of the two enzymes. As a result, the processing of the signals transduced by the composite biomaterial interface in the presence of the two substrates permits the assay of the... 

For cadmium, Weigel (1985 a, b) concluded that, in vitro, this metal inhibits photosynthesis mainly by interaction with several sites in the Calvin cycle and not by interaction with photochemical reactions located on the thylakoid membrane. In vitro studies showed a 90% inhibition of phosphoribulokinase (EC 2.7.1.18) by cadmium ions (Hurwitz et al., 1956). This element also inhibited light activation of the Calvin cycle enzymes glyceraldehyde-3-phosphate kinase (EC 1.2.1.13) and ribulose-5-phos-phate kinase (EC 2.7.1.19) in mesophyll protoplasts of Valerianella locusta (Weigel,... 

Photoreaction can remove thymidine-thymidine photodimers. Visible light activates the enzyme DNA photolyase. This enzyme absorbs visible light and transfers that energy to the photodimer, reversing the dimerization directly. 

The mechanism by which reversible phosphorylation occurs is a central part in our understanding of the overall regulation process. It is currently described by the interplay of a continuously active phosphatase and a light-activated kinase (Allen et al., 1981). The activation of the latter enzyme can be produced in experimental conditions where the intersystem electron carriers are in a reduced state. Indirect evidence have favored kinase activation by the reduced plastoquinones (Allen et al., 1981)... 

The lack of reactivity of the semiquinone per se with either thioredoxin or NADPH shows that it cannot be involved in catalysis. The rapid production of semiquinone by irradiation of partially reduced enzyme is a light-activated disproportionation since it is totally dependent upon the presence of some oxidized enzyme. Enzyme fully reduced by dithionite forms no semiquinone, while enzyme partially reduced by dithionite rapidly forms semiquinone upon irradiation. Furthermore, the light-activated disproportionation of enzyme first reduced with NADPH results in the reduction of NADP. Thus, FAD catalyzes the disproportionation in keeping with the known photosensitizing nature of free flavins. This reaction is reversed slowly (half-time ca. 150 min 25°) in the dark. The semiquinone is rapidly reoxidized by oxygen to yield an enzyme with unaltered spectral and catalytic properties (58). Similar reactions have been very briefly reported for lipoamide dehydrogenase the dark reverse reaction is comparatively rapid, being complete in 30 min (16S). 

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