3-azido-L-tyrosine as a photoinhibitor of tubulin:tyrosine ligase. Role of thiol groups.

We have synthesized the photoactivatable probes 3-azido-L-tyrosine and p-azido-L-phenylalanine and studied their capacity to inhibit the incorporation of [3H]tyrosine into tubulin catalyzed by tubulin:tyrosine ligase. Without illumination, only 3-azido-L-tyrosine reversibly inhibits the enzyme. Upon illumination, both reagents irreversibly photoinactivate the enzyme in a similar way. The ligase can be protected against photoinactivation by reversibly blocking essential thiol groups with pCMB during illumination.