Photo- and thermal-activation of bovine liver urocanase

In the photoactivation of sulfite-modified urocanase from Pseudomonas putida, the sulfite adds to the nicotinamide adenine dinucleotide and photodissociation accompanies activation. Bovine urocanase contains the same coenzyme. The purpose was to find if sulfite can inactivate a mammalian urocanase and if UV light can reactivate the enzyme. It was inactivated by sulfite, 10-100 μM, and dialysis did not restore activity. Near-UV light (11 W m-2) reactivated the enzyme in 45 min. A competitive inhibitor protected urocanase from sulfite, showing that sulfite acts at the active site. The modification was dependent on temperature, time, and concentration of sulfite. The modification was reversed by incubation at 250C for 24 h. These results resemble those found with the P. putida urocanase. It is likely that these thermal- and photo-reactions are the same for the bacterial and mammalian urocanases. (author)