Table 2.

Kinetic constants of purN heterodimers

Enzyme	Km (GAR), μM	Km (fDDF), μM	kcat, s−1	kcat/Km (GAR), μM−1⋅s−1
A46	159  ±  5	31.4  ±  3.9	∼8	∼0.05
B13	196  ±  34	120  ±  16	∼12	∼0.06
WT	118  ±  3	12.3  ±  1.3	90 ± 2	0.76

GAR and fDDF were obtained and kinetic measurements were performed as described (30). Wild-type E. coli PurN was prepared as described by using a pMSW2 vector in MW12 cells (19). Heterodimer PurN was prepared by the same method using the vectors isolated from the positives (pDIM-N2 and pDIM-C6) and TX680F′ cells. Heterodimer concentration was estimated by densitometry of SDS/PAGE separation of the most active gel filtration fraction.