In enzymology, a queuine tRNA-ribosyltransferase (EC 2.4.2.29) is an enzyme that catalyzes the chemical reaction

[tRNA]-guanine + queuine [tRNA]-queuine + guanine

Thus, the two substrates of this enzyme are tRNA-guanine and queuine, whereas its two products are [tRNA]-queuine and guanine.

This enzyme belongs to the family of glycosyltransferases, specifically the pentosyltransferases. The systematic name of this enzyme class is [tRNA]-guanine:queuine tRNA-D-ribosyltransferase. Other names in common use include tRNA-guanine transglycosylase, guanine insertion enzyme, tRNA transglycosylase, Q-insertase, queuine transfer ribonucleate ribosyltransferase, transfer ribonucleate glycosyltransferase, tRNA guanine transglycosidase, guanine, queuine-tRNA transglycosylase, and tRNA-guanine:queuine tRNA-D-ribosyltransferase.

As of late 2007, 36 structures have been solved for this class of enzymes, with PDB accession codes 1EFZ, 1ENU, 1F3E, 1IQ8, 1IT7, 1IT8, 1J2B, 1K4G, 1K4H, 1N2V, 1OZM, 1OZQ, 1P0B, 1P0D, 1P0E, 1PUD, 1PXG, 1Q2R, 1Q2S, 1Q4W, 1Q63, 1Q65, 1Q66, 1R5Y, 1S38, 1S39, 1WKD, 1WKE, 1WKF, 1Y5V, 1Y5W, 1Y5X, 2ASH, 2BBF, 2QII, and 2QZR.

• Howes NK, Farkas WR (1978). "Studies with a homogeneous enzyme from rabbit erythrocytes catalyzing the insertion of guanine into tRNA". J. Biol. Chem. 253 (24): 9082–7. doi:10.1016/S0021-9258(17)34288-6. PMID 721832.
• Nishimura S; Noguchi, S; Kasai, H; Shindo-Okada, N; Ohgi, T; Goto, T; Nishimura, S (1979). "Novel mechanism of post-transcriptional modification of tRNA Insertion of bases of Q precursors into tRNA by a specific tRNA transglycosylase reaction". J. Biol. Chem. 254 (8): 3067–73. doi:10.1016/S0021-9258(17)30183-7. PMID 372186.
• Shindo-Okada N, Okada N, Ohgi T, Goto T, Nishimura S (1980). "Transfer ribonucleic acid guanine transglycosylase isolated from rat liver". Biochemistry. 19 (2): 395–400. doi:10.1021/bi00543a023. PMID 6986171.