Human photoreactivating enzyme action spectrum and safelight conditions.

The action spectrum for photoreactivation by enzymes from human leukocytes and fibroblasts extends from 300 to approximately 600 nm with a maximum near 400 nm. The ability of the human enzymes to utilize light of wavelengths greater than 500 nm suggested that yellow or gold lights conventionally used as safelights for photoreactivation might serve as sources of photoreactivating light for these enzymes. Experiments using lights with a range of spectral outputs confirm that the standard yellow "safe" lights do produce photoreactivation by the human but not the Escherichia coli enzyme.