Table 2. Pyrophosphate-exchange activity of EcMetRS and MtMetRS.

Enzyme	K m Met (µM)	K m ATP (µM)	k cat † (s−1)	K cat/K m ‡ (s−1 µM −1)
MtMetRS	50 ± 11	4282 ± 1475	6 ± 1	0.0015
EcMetRS§	21 ± 4	528 ± 91	74 ± 8	0.14

^† k _cat is the average of the values for methionine and ATP.

^‡ K _m is the K _m for ATP.

^§Ghosh et al. (1991 ▸).