Front Matter

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Fatty acids, alcohols, amides and other compounds which are able to establish

hydrogen bonds with Arg 47 and/or Thr 51 will be hydroxylated. Esters and nonpolar

compounds such as alkanes, which are unable to create these interactions or which

cannot path the “hydrophobic mouth” at the beginning of the substrate access chan-

nel, are not or only marginally converted by P450 BM-3. Regioselectivity of the

subterminal fatty acid hydroxylase P450 BM-3 depends strongly on the chain-

length of the fatty acid substrate (Table 3).

Truan and co-workers (Truan et al., 1999) determined the absolute configuration

of three primary metabolites obtained from palmitic acid showing high enantiomeric

excess for (R)-15- and (R)-14-hydroxypalmitic acid (both 98 % ee) and somewhat

lower selectivity forx-3 hydroxylation (72 % ee) yielding (R)-13-hydroxypalmitic

acid. Arachidonic acid is metabolized by P450 BM-3 to nearly enantiomerically pure

(R)-18-hydroxyeicosatetraenoic acid (80 % of total products) and 14(S),15(R)-

epoxyeicosatrienoic acid (20 % of total products). The arachidonic acid analogs

eicosapentaenoic acid and eicosatrienoic acids were converted quantitatively to

17(S),18(R)-epoxyeicosatetranoic acid or 17-, 18-, and 19-hydroxyeicosatrienoic

acid in a ratio of 2.4 : 2.2 : 1 (Capdevila et al., 1996). In addition to hydroxyla-

tion, Boddupalli and co-workers observed the formation of ketones such as 14-

oxo- and 13-hydroxy-14-oxo-palmitic acid, which was related to a dehydrogenase

402 18 Fatty Acid Hydroxylations using P450 Monooxygenases

Table 3.Regioselectivity of P450 BM-3 catalyzed hydroxylations of aliphatic substrates (Miura and
Falco, 1975).


Substrate Chain-length Distribution of hydroxyl isomersa[%]


x-1 x-2 x-3

Fatty acid 12 36 30 34


13 17 65 18
14 44 28 28

15 32 49 19
16 31 48 21
17 49 35 16

18 39 47 14

Alcohol 12 22 51 27


13 24 49 27
14 30 44 26

15 27 54 19
16 22 41 37

Amide 12 21 45 34


14 34 34 32

15 28 57 15
16 29 45 26

amajor products are highlighted in bold numbers

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