Table 1.

Steady state kinetic parameters of IMPDH from various organisms.

IMPDH	kcat (s−1)	Km IMP (μM)	Km NAD+ (μM)	Kii NAD+ (mM)	Ki MPA (nM)
Human type I	1.2-1.8a	14-18a	42-70a	2.0b	11-33c
Human type II	0.4-1.4d	4-9d	6-32d	0.59e	7-14f
Aerobacter aerogenes t	n.d.	60	800	n.d.	n.d.
Borellia burgdorferi g	2.6	30	1100	2.3	8,000
Cryptosporidium parvum h	3.3	29	150	2.9	9,300
Escherichia coli	13i	61i	2000i	2.8i	~20,000j
Helicobacter pylori k	3.0	18	73	1.7	n.d.
Mycobacterium tuberculosis l	0.53	78	1000	5.0	62,000
Streptococcus pyogenes m	24	62	1180	n.d.	>10,000
Tritrichomonas foetus n	1.9g	1.7g	150g	6.8g	9,000g

n.d., no data. Assay buffers are generally similar, but temperature varies between 25-37 degrees C. Values of k_cat are reported per active site, not per tetramer. Note that while C. parvum and T. foetus are protozoan parasites, their IMPDHs are most similar bacterial enzymes, suggesting that the genes where obtained by horizontal transfer.

^a[80, 81] [82];

^b[82];

^c[80, 81];

^d[80, 81, 83];

^e[83];

^f[57, 80, 84];

^g[85];

^h[66];

ⁱ[86];

^jN. Benfield and L. Hedstrom, unpublished data;

^k[24];

^l[62];

^m[78];

ⁿ[87].