Table 1.

Kinetic constants for human PNPOx

Substrate	Km or Ki (μM)	kcat (sec−1)
PNP	1.8 (2.0)a	0.19 (0.3)a
PMP	1.0 (105)b	0.20 (1.7)b
PLP	3.2 (8.0)b	—

Activity determined in 50 mM Tris buffer (pH 7.6).

^a Values previously determined for Escherichia coli PNPOx at pH 7.6 (Yang and Schirch 2000).

^b Values determined in Tris at pH 8.5 (Yang and Schirch 2000).