. Author manuscript; available in PMC: 2018 Apr 30.

Published in final edited form as: Biochemistry. 2017 Nov 21;56(48):6368–6376. doi: 10.1021/acs.biochem.7b01027

Table 1.

V/K KIEs, Intrinsic KIEs, and Calculated KIEs for PfHGXPRT at Four Atomic Positions

heavy substrate	starting material	light substrate	type of KIE	V/K KIE	intrinsic KIE	calculated KIE^e
1-¹⁴C	[1-¹⁴C]ribose	5-³H₂	PRPP primary	1.025 ± 0.004^b	1.025 ± 0.004^c	1.031
1-³H	[1-³H]ribose	5-¹⁴C^a	α-secondary Hypoxanthine	1.205 ± 0.006	1.205 ± 0.006^c	1.212
7-¹⁵N	[7-¹⁵N]adenine	hypoxanthine	β-secondary	0.988 ± 0.009	N/A^d	0.984
9-¹⁵N	[9-¹⁵N]adenine	hypoxanthine	primary	0.997 ± 0.005	N/A^d	1.014

The KIE value from the remote 5-¹⁴C label is assumed to be unity.

This experimental V/K KIE value is dependent on the remote 5-³H₂ KIE according to the expression KIE_V_/_K = KIE_observed × KIE_remote. In this system, no correction is needed.

The intrinsic KIE values were determined by correcting V/K KIE values using eq 7 assuming C_f = 0.001.

N/A, not applicable; the forward commitment factor was not measured for this substrate.

The calculated KIE values [Gaussian 09, B3LYP level of theory, and 6-31g(d) basis set]²⁶ correspond to those for the final transition state model shown in Figure 5.