Table 1 Kinetic constants for the naturally occurring substrates of TbrHGPRT, TcrHGPRT and human HGPRT.

From: Crystal structures and inhibition of Trypanosoma brucei hypoxanthine–guanine phosphoribosyltransferase

Substrate

Km (μM)

kcat (s−1)

kcat/Km (μM−1s−1)

TbrHGPRT

 Guaninea

2.3 ± 0.4

23.8 ± 0.3

10.3

 Hypoxanthinea

5.5 ± 0.3

17.1 ± 0.3

3.1

 Xanthinea

Weak activity

 PRib-PPa

103 ± 16

  

TcrHGPRTb,c

 Guanine

9.9 ± 0.29

41.2 ± 2.9

4.2

 Hypoxanthine

8.6 ± 1.0

23

2.7

 Xanthine

No activity reported

 PRib-PP

32.4 ± 3.1

  

Human HGPRTd

 Guanine

1.9 ± 0.4

8.2 ± 0.6

4.3

 Hypoxanthine

3.4 ± 1.0

5.2 ± 0.4

1.5

 Xanthine

Not a substrate

 PRib-PP

59.6 ± 6

  
  1. a0.03 M phosphate buffer, 0.012 M MgCl2 and 1 mM of DTT, pH 7.4.
  2. b(Canyuk et al.)43.
  3. c(Allen & Ullman)54.
  4. d(de Jersey et al.)10.
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