Table 2.

Kinetic parameters of inosine-5'-monophosphate and guanosine-5'-monophosphate synthesis using HPRT from various organisms.

Substrate	Km, μМ	Vmax, μmol/min·mg	kcat, 1/s	kcat/Km, 1/M·s
Thermus thermophilus HB27
hypoxanthine	13 ± 4	28 ± 9	9 ± 3	6.9 × 105
guanine	28 ± 9	6 ± 2	2.0 ± 0.7	7.1 × 104
PRPP	220 ± 60	17 ± 5	6 ± 2	2.7 × 104
Thermus thermophilus HB8 [12]
hypoxanthine	3.9 ± 1.5	–	9.1 ± 0.8	–
guanine	7.4 ± 1.7	–	18 ± 1	–
PRPP	68 ± 18	–	20 ± 2	–
Homo sapiens [13]
hypoxanthine	3.8 ± 0.3	–	2.6 ± 0.6	7 × 105
PRPP	19.1 ± 1.6	–	2.5 ± 0.05	1 × 105
Escherichia coli [14]
Hypoxanthine	37	–	–	–
PRPP	330	–	–	–