interactions (Ortiz de Montellano et al., 1992). P450 hydroxylases which preferable
produce subterminal hydroxylated fatty acids are generally less specific cytochrome
P450 enzymes which usually accept a wider substrate range and thereby generate
two or more hydroxylation products (Table 1).
The oxidative reaction does not always stop after monohydroxylation, and further
oxidation products such as aldehydes, ketones and carboxylic acids are often formed
(Boddupalli et al., 1990, 1992). Interestingly, for P450 BM-3, a fatty acid hydroxy-
lase fromBacillus megaterium(Ruettinger, 1989), it was shown that the composition
of the initial and further oxidation products depends on the oxygen supply in the
reaction solution (Schneider et al., 1999).
A large number of P450 enzymes of the gene familiesCYP4,CYP52 andCYP 102
are known to catalyze fatty acid hydroxylations. Only well-characterized and recom-
binantly expressed P450s are presented in more detail in Table 1 and the following
survey.
18.4.1 TheCYP102 family
This family consists of only three members of which one – produced by the strain
Bacillus megaterium– is able to catalyze the hydroxylation of fatty acids with the yet
highest reported, turnover numbers for P450 monooxygenases in the range of> 1000
equiv min–1. The corresponding enzyme is named P450 BM-3 and was cloned and
functionally expressed inE. coli(Narhi and Fulco, 1986, 1987; Ruettinger et al.,
1989).
P450 BM-3 (CYP102) is a water-soluble heme enzyme having a molecular weight
of 118 kDa. It is a natural fusion protein containing the P450 and reductase part on
one polypeptide chain (Narhi and Fulco, 1987; Ruettinger et al., 1989). The heme
domain (Ravichandran et al., 1993; Li and Poulos, 1997) and reductase domain
(Sevrioukova et al., 1999) were crystallized separately in the presence and/or ab-
sence of palmitoleic acid. From the four crystallized P450 enzymes known to
date (Poulos et al., 1987; Ravichandran et al., 1993; Hasemann et al., 1994; Park
et al., 1997), P450 BM-3 shows the highest sequence homology to eucaryotic
P450 systems, and serves as preferred structural model (Burke et al., 1997; Le-
wis, 1998, 1999; Lewis and Lee-Robichaud, 1998).
18.4 Fatty Acid-hydroxylating P450s Monooxygenases 399
Figure 2. P450-catalyzed hydroxylations of fatty acids occur at different positions.