P1, P3‐bis(5′‐adenosyl)triphosphate (Ap3A) as a substrate and a product of mammalian tryptophanyl‐tRNA synthetase
- 22 August 1994
- journal article
- Published by Wiley in FEBS Letters
- Vol. 350 (2-3) , 287-290
- https://doi.org/10.1016/0014-5793(94)00764-0
Abstract
Bovine tryptophanyl-tRNA synthetase (TrpRS, E.C. 6.1.1.2) is unable to catalyze in vitro formation of Ap4A in contrast to some other aminoacyl-tRNA synthetases. However, in the presence of l-tryptophan, ATP-Mg2+ and ADP the enzyme catalyzes the Ap3A synthesis via adenylate intermediate. Ap3A (not Ap4A) may serve as a substrate for TrpRS in the reaction of E·(Trp ∼ AMP) formation and in the tRNATrp charging. The Km value for Ap3A was higher than the Km for ATP (approx. 1.00 vs. 0.22 mM) and Vmax was 3 times lower than for ATP. The Zn2+-deficient enzyme catalyzes Ap3A synthesis in the absence of exogenous ADP due to ATPase activity of Zn2+-deprived TrpRS. The inability of mammalian TrpRS to synthesize Ap4A, might be considered as a molecular tool preventing the removal of Zn2+ due to chelation by Ap4A and therefore preserving the enzyme activityKeywords
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