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. Author manuscript; available in PMC: 2008 Dec 8.
Published in final edited form as: Biochemistry. 2006 Oct 31;45(43):13054–13063. doi: 10.1021/bi060591r

Table 4.

Comparison of the Rate Determining Events for AKR1C2, AKR1C9, AKR1B1, AKR2B5.

Enzyme AKR1C2 AKR1C9a AKR1B1d AKR2B5e
Substrate DHT DHT Xylose Xylose
Cofactor NADPH NADPH NADPH NADH
kcat (s−1) 0.033 0.30 0.19 14.2
Km (μM) 2.9 0.7 1 × 103 7.8 × 104
kcat/Km (M−1 s−1) 9.3 × 103 4.3 × 105 190 140
Dkcat 1.5 2.3b 1.00 1.55
D(kcat/Km) 2.1 3.0b 1.82 2.09
ktrans (s−1) 0.11 1.9c 76 na
Dktrans 3.5 Na 3.6 na
kred (s−1) 0.12 Na 130 170
kPr (s−1) 0.081 Na 1 × 106 1 × 105
kQr (s −1) 0.21 Na 0.18 19.6f
a

Rate constants as reported (25).

b

These values are the averages of the previously reported and more recent measurements (Cooper and Penning., unpublished results).

c

This value is from more recent measurements.

d

Rate constants as reported (23).

e

Rate constants as reported (24).

f

This kQr value is calculated based on the reported (24) microscopic rate constants. na, not available.