. Author manuscript; available in PMC: 2009 Dec 1.

Published in final edited form as: Arch Biochem Biophys. 2008 Sep 18;480(1):58–67. doi: 10.1016/j.abb.2008.08.024

Table 4.

Comparison of K_m and K_i Estimates for Wild-Type and Mutant MDDs.^a

Enzyme	K_m(R,S-MVAPP)^a (μM)	Fold Inflation	K_i(R,S-DPGP)^b (μM)	Fold Inflation	K_i(R)-FMAVPP)^c (μM)	Fold Inflation
WT	28.9±3.3	-	2.3±0.3	-	0.062±0.005	-
N17A	425±74	14.7	368±27^d	160	2.6±0.4	42

Inhibition experiments were performed as described in Methods. Spectrophotometric assays (30°C) employed the method of Cardemil and Jabalquinto [16]. K_i values were estimated by fitting the data (Sigmaplot/Enzyme Kinetics module) to a competitive inhibition model using the equation velocity = V_max[S]/(K_m(1+[I]/K_i) + [S]). Standard errors of the fits are indicated.

(R,S)-diphosphoglycolyl proline (DPGP) concentrations ranged from 2.4 – 4.8 times the K_i value for WT and 0.8 – 3.3 times K_i value for N17A.

(R)-6-fluoromevalonate diphosphate (FMVAPP) concentrations ranged from 0.5 – 8 times the K_i value for WT and from 1.3 – 3.5 times the K_i value for N17A.

This inhibitor constant was determined using standard assay conditions (8 mM ATP). Measurements performed at elevated (20 mM) ATP indicated a K_i value of 161 μM.