TABLE 2.

Rate constants for peptidyl transfer of active site mutants

	fMetPm (sec−1)	fMetCPm (sec−1)	fMetPhePm (sec−1)a	fMetPheCPm (sec−1)
Wild-type	1.2 ± 0.2a	18.9 ± 0.7	9.4 ± 2.5	11.9 ± 2.9
A2451U	0.07 ± 0.02a	2.6 ± 0.6	0.05 ± 0.009b	3.3 ± 0.6b
A2451C	0.04 ± 0.02	1.0 ± 0.3	2.8 ± 0.04b,c 0.04 ± 0.007b,c	0.6 ± 0.5b
A2451G	0.01 ± 0.002	0.2 ± 0.006	0.02 ± 0.004b	0.7 ± 0.8b
U2506C	0.003 ± 0.0002a	0.2 ± 0.1	0.002 ± 0.0003b	0.4 ± 0.2
U2506G	0.005 ± 0.001	0.04 ± 0.01	0.002 ± 0.0003b,d	0.08 ± 0.02b
U2506A	0.009 ± 0.005	0.4 ± 0.01	0.001 ± 0.0004b	0.4 ± 0.01b
U2585C	0.02 ± 0.00a	1.2 ± 0.1	0.02 ± 0.007	2.0 ± 0.8
U2585G	0.3 ± 0.04	2.0 ± 0.05	1.3 ± 0.07	8.6 ± 2.8
U2585A	0.05 ± 0.003	1.6 ± 0.04	0.02 ± 0.009	5.3 ± 2.5
A2602C	0.005 ± 0.0006a	0.01 ± 0.006	0.03 ± 0.009	0.8 ± 0.3
A2602U	0.04 ± 0.02	0.07 ± 0.002	0.3 ± 0.1	1.9 ± 0.4
A2602G	0.01 ± 0.004	0.03 ± 0.01	0.07 ± 0.02	0.9 ± 0.7

PT reactions were carried out in buffer A at pH 7.5 and 10 mM Pm or CPm and, unless otherwise indicated. 7 mM Mg²⁺ and 20° C. The error listed is the standard deviation in the rate constants from at least two experiments.

^aData from Youngman et al. (2004).

^bRate constant measured at 15 mM Mg²⁺.

^cTime courses for the fMetPhePm reaction on A2451C ribosomes consistently fit to double exponential curves. The rate constants for the first and second phases are reported where the first phase typically proceeds to an amplitude of 0.2 and the second phase to 0.5.

^dRate constant measured at 37° C.