Krauspe R, Lavrik OI. Photoaffinity labeling of chloroplastic and cytoplasmic leucyl-tRNA synthetases of Euglena gracilis by the gamma-(p-azidoanilidate) of ATP.
EUROPEAN JOURNAL OF BIOCHEMISTRY 1983;
132:545-50. [PMID:
6406221 DOI:
10.1111/j.1432-1033.1983.tb07396.x]
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Abstract
The photoreactive gamma-(p-azidoanilidate) analog of ATP, AzAnATP, was used to affinity-label the chloroplastic and cytoplasmic leucyl-tRNA synthetases of Euglena gracilis. The analog is able to replace the substrate ATP in the tRNA leucylation reaction catalyzed by both enzymes. In the presence of ATP, it is a competitive inhibitor against ATP as well as leucine for the two isoenzymes, as is also shown for the photoinactive gamma-anilidate analog of ATP, AnATP, which does not serve as substrate in the enzyme reaction. During ultraviolet irradiation, the enzymes are irreversibly inactivated by AzAnATP in a concentration-dependent and time-dependent manner indicative of photoaffinity labeling. Both ATP and leucine, but not tRNA, protect the enzymes against ultraviolet-induced inactivation by AzAnATP. Comparative kinetic characterization of the inactivation process reveals differences in the active centers of the two intracellular isoenzymes.
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