Reactive oxygen species in photochemistry of the red fluorescent protein "Killer Red".

The fluorescent protein aptly named "Killer Red" (KRed) is capable of killing transfected cells and inactivating fused proteins upon exposure to visible light in the presence of oxygen. We have investigated the source of the bioactive species through a variety of photophysical and photochemical techniques. Our results indicate a Type I (electron transfer mediated) photosensitizing mechanism.