Sulfonation of other substrates

 Triclosan sulfate was formed rapidly, with the overall kinetics conforming to a

hyperbolic curve (eq. 1) (Table 3-2). Substrate inhibition was observed for 4'-OH-PCB79

(Figure 3-4), with the data fitting equation (3). The value of K, that gave the best fit was

217 f 25 CLM (Table 3-2). Sulfate conjugation of 4'-OH-PCBl59 and 4'-OH-PCBl65,

which proceeded via Michaelis-Menten kinetics, was, respectively, 11 and 5 times less

efficient than the sulfonation of 4'-OH-PCB79 (Table 3-2). At a concentration of 10 CLM,

4'-OH-PCBl165 was observed to inhibit sulfonation of substrates already present in polar

bear liver cytosol by 60%.


Table 3-2. Kinetic parameters (Mean f SD) for the sulfonation of various xenobiotics by
 polar bear liver cytosol, listed in order of decreasing enzymatic efficiency.
 All data fit equation (1), except for 4'-OH-PCB79 and PCP, which fit
 equations (3) and (2) respectively (see Methodology for equations).

Substrate Vmax Km Vmax / Km Ki
 (pmol/min/mg) (yM) (pL/min/mg) (yM)


triclosan 1008 f 135 11 f 2
4'-OH-PCB79 372 f 38 123 f 20
OHMXC 51.1 f 7.8 67 f 4
4'-OH-PCBl165 8.6 f 2.0 17 f 7
TCPM 62.0 f 11.2 144 f 36
4'-OH-PCBl159 14.8 f 2.3 60 f 21
PCP 13.8 f 1.2 72 f 14b
aK, for bears G, K and X were 240, 220 and 190 LM
constrained to obtain the best fit for the data
bSso; h = 2.0 f 0.4


 90.8 f 6.8
 3.1 f 0.3 217 f 25a
 0.8 f 0.1
 0.56 f 0.17
 0.44 f 0.06
 0.28 f 0.12
 0.20 f 0.05
respectively. These values were