This mechanism is based on the following arguments: (a) Atmospheric oxygen is required for fluorescence to develop (21,24). (b) Fluorescence of anaerobically preformed GFP develops with a simple exponential time course after air is readmitted (21,25), which is essentially unaffected by the concentration of the GFP itself or of cellular cofactors. (c)An alogous imidazol in one saut oxidize spontaneously(26).(d)Theproposed