Reversible Inhibition of Bioluminescence

The reversible inhibition of luminescence can be achieved by a variety of methods that block luminescence or remove one of the components essential for luminescence, as explained below. 

Effect of pH. The light emission from most bioluminescence systems is affected by the pH of the medium, and some luciferases and photoproteins can be made inactive at certain pH ranges without resulting in permanent inactivation. For example, the luminescence of euphausiids can be quenched at pH 6, the luminescence of aequorin can be suppressed at pH 4.2-4A, and the luciferase of the decapod shrimp Oplophorus becomes inactive at about pH 4. In the case of Cypridina luminescence, however, the acidification of an extract to below pH 5 results in an irreversible inactivation of the luciferase. 

Elimination of a cofactor needed for luminescence. The chelators EDTA and EGTA efficiently quench the luminescence of Ca2+-activated systems such as aequorin, obelin and mnemiopsin. The luminescence systems that require ferrous ions, such as extracts of the polychaete Chaetopterus, can be inhibited by 8-hydroxyquinoline and 

When H2O2 is a necessary component of a luminescence system, it can be removed by catalase. If a luminescence system involves superoxide anion, the light emission can be quenched by destroying O2 with superoxide dismutase (SOD). The ATP cofactor usually present in the fresh extracts of the fireflies and the millipede Luminodesmus can be used up by their spontaneous luminescence reactions, eventually resulting in dark (nonluminous) extracts containing a luciferase or photoprotein. The process is, however, accompanied by a corresponding loss in the amount of luciferin or photoprotein. The use of ATPase and the elimination of Mg2+ in the extract may prevent such a loss. 

Anaerobic condition. Molecular oxygen is an essential requirement in a majority of bioluminescence systems. Thus, the light emission from those systems stops if molecular oxygen is completely eliminated. The methods for removing oxygen from biological fluids were discussed in detail by Harvey (1926b), which contains useful information on various procedures that are valuable even today. 

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