TABLE 3.

Kinetic parameters of P. aeruginosa and M. barkeri PBGSs and IC₅₀s for alaremycin^a

Parameter	P. aeruginosa	M. barkeri
General catalytic properties
Km(μM)	0.32	0.07
kcat (s−1)	16.1	0.012
kcat/Km (μM−1s−1)	50.3	0.17
Inhibition by alaremycin
IC50 (mM)	2.1	2.2
ki (mM)	1.33	1.51

^aThe Michaelis-Menten constant (K_m) and the k_cat and the k_cat/K_m values for the PBGSs were determined from substrate velocity plots by measuring the constant velocity formation of porphobilinogen from ALA over a substrate concentration range of from 1 to 10 mM. Values were determined by the use of iterative, curve-fitting Lineweaver-Burk plots (SigmaPlot program, version 8.0; Enzyme Kinetics program, version 1.1). For inhibition studies, 0 to 40 mM alaremycin was added to the enzyme activity test. The standard errors of the results were between 5 and 10%.