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. 2016 Jun 17;44(16):7511–7526. doi: 10.1093/nar/gkw551

Figure 3.

Figure 3.

Guanylyltransferase reaction. The GTase reaction consists of two steps: protein self-guanylylation and the transfer of the GMP group to the 5′ diphosphate RNA. The GTase reaction catalyzed by chlorella virus PBCV-1 capping enzyme is highly reversible. A detailed kinetics study of the forward and reverse reaction of both steps revealed that in the absence of RNA substrate, the kcat/Km value of the reverse reaction of the first step (the pyrophosphorolysis of the lysyl-Nζ-5′-phosphoguanosine intermediate into lysine and GTP) is 120 times higher than that of the forward reaction. The second step (the transfer of the GMP moiety from the lysyl-Nζ-5′-phosphoguanosine to diphosphate 5′ end) is largely forward-tending, with a 10-fold difference in the kcat/Km values (96).