title: Mechanism-based inactivation of tRNA-guanine transglycosylase from Escherichia coli by 2-amino-5-(fluoromethyl)pyrrolo[2,3-d]pyrimidin-4 (3H)-one.
abstract: In Escherichia coli, tRNA-guanine transglycosylase (TGT) catalyzes the incorporation of the queuine precursor preQ1 [2-amino-5-(aminomethyl)pyrrolo[2,3-d]pyrimidin-4(3H)-one] into tRNA. This precursor is further elaborated to queuine by two subsequent enzymic reactions [Slany, R. K., & Kersten, H. (1994) Biochimie 76, 1178-1182]. Our previous studies [Hoops, G. C., Townsend, L. B., & Garcia, G. A., (1995) Biochemistry (in press)] on a series of synthetic 5- and 6-substituted 2-aminopyrrolo[2,3-d]pyrimidin-4(3H) -ones have revealed that the E. coli TGT tolerates a wide diversity of substituents (isosteric, or nearly so, to the aminomethyl group of preQ1) at the 5 position. We report here that 2-amino-5-(fluoromethyl)pyrrolo[2,3-d]pyrimidin-4 (3H)-one (FMPP) inactivates TGT in a time- and concentration-dependent manner with k(inact) = 0.074 min-1 and KI = 136 microM. A competitive inhibitor (7-methyl-preQ1), with respect to preQ1, of TGT [Hoops, G.C., Townsend, L.B., & Garcia, G.A. (1995) Biochemistry (in press)] protects the enzyme from inactivation by FMPP. FMPP also acts as a competitive inhibitor (KI = 114 microM) of TGT under initial velocity conditions. The rate of fluoride release from FMPP is slightly faster (0.064 min-1) than the k(inact) (0.053 min-1) at 300 microM FMPP, consistent with fluoride release preceding inactivation. FMPP appears to partition between "normal" turnover (kcat = 0.461 min-1 and Km = 152 microM), inactivation, and an alternative processing to an unidentified, fluoride-released product.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D004791:Enzyme Inhibitors / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology*; D010430:Pentosyltransferases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011744:Pyrimidinones / Q000378:metabolism*; D011758:Pyrroles / Q000378:metabolism*; D012343:RNA, Transfer / Q000378:metabolism*
chemical_list: C097002:2-amino-5-(fluoromethyl)pyrrolo(2,3-d)pyrimidin-4(3H)-one; D004791:Enzyme Inhibitors; D011744:Pyrimidinones; D011758:Pyrroles; D012343:RNA, Transfer; D010430:Pentosyltransferases; C020837:queuine tRNA-ribosyltransferase