The discovery of the photoactivation of urocanase in Pseudomonas putida by ultraviolet light at this laboratory has been followed by investigations of the nature of the photochemical activation step and the dark reversion to the inactive enzyme. NAD plus, tightly bound to urocanase, forms an adduct with sulfite which blocks the active site. Sulfite may arise enzymatically from cysteine sulfinate; the NAD-SO3-adduct is photochemically dissociated by light absorbed at 320 nm, thus restoring the catalytic activity. Light at 280 nm is also effective; the chromophore for this effect transfers energy to the NAD-SO3- adduct. One goal of the proposed work is to futher elucidate and establish the means by which this activation by 280 nm light occurs. Studies on the chemical and physical properties of urocanase will be undertaken especially with respect to understanding the photoactivation and dark inactivation processes.
