18.4.2 TheCYP52 family
Members of theCYP52 family have been found inCandidaspecies such asC. mal-
tosa(Schunck et al., 1989; Ohkuma et al., 1995),C. apicola(Lottermoser et al.,
1996) andC. tropicalis(Seghezzi et al., 1992). They catalyze the terminal hydro-
xylation ofn-alkanes, which represents the first and rate-limiting step in the alkane
degradation pathway, and thex-hydroxylation of fatty acids (Scheller et al., 1998).
Most of theseCYP52 genes were shown to be inducible byn-alkanes, alkenes, hy-
droxycarboxylic acids and carboxylic acids. In the yeastCandida maltosa– the
mainly investigatedCandidaspecies – eight structurally relatedCYP52A genes
have been identified (Zimmer et al., 1996). The characterization of these P450s
resulted in a phylogenetic tree (Zimmer et al., 1998a) which describes the evolution-
ary distance among the members of theCYP52A family. This is also reflected by the
differences in their substrate specificity. For instance, CYP52A3 isoenzymes (P450
Alk1A, P450 Cm1) prefer alkanes, CYP52A4 (P450 Alk3A, P450 Cm2) and
CYP52A5 (P450 Alk2A) hydroxylate alkanes and fatty acids in similar extents,
whereas CYP52A9 (P450 Alk5A), CYP52A10 and CYP52A11 prefer fatty acids
as substrates. The individual substrate specificities are in good agreement to the
inducer used for P450 expression (Ohkuma et al., 1995; Zimmer et al., 1996, 1998a).
As shown in Table 4, even the majorn-alkane-inducible P450 form ofC. maltosa,
CYP52A3, catalyzes thex-hydroxylation of lauric, myristic, and palmitic and oleic
acid in remarkable turnover numbers between 5 and 41 equiv min–1. The upon al-
kane induction ofC. maltosaonly poorly formed CYP52A10 and CYP52A11 en-
zymes failed to convert hexadecane, and could not initiate the first step of the alkane
degradation pathway. However, lauric acid was found to be converted much more
efficiently than palmitic acid by CYP52A10 and CYP52A11 (Zimmer et al., 1998a).
Interestingly, all of these P450 enzymes have a carboxylic acid hydroxylation ac-
tivity and Scheller and co-workers found that a single P450 enzyme, CYP52A3
fromC. maltosa, catalyzes the complete oxygenation cascade starting fromn-al-
404 18 Fatty Acid Hydroxylations using P450 Monooxygenases
Table 4.Turnover numbers in the fatty acid hydroxylation activity of P450 enzymes of theCYP52A
family.
P450 Turnover[equiv min–1] References
LA MA PA OA DD HDAlk1A, Cm1 6 13 16 26 44 48 Zimmer et al., 1996
Alk2A 22 23 22 43 26 22 Zimmer et al., 1996
Alk3A 23 41 7 5 26 23 Zimmer et al., 1996
Cm2 40 42 3 2 24 20 Zimmer et al., 1996
Alk5A 33 41 51 81 2 12 Zimmer et al., 1996
CYP52A10 3.6 n.m. 0.2 n.m. n.m. <0.1 Zimmer et al., 1998a
CYP52A11 4.0 n.m. 0.25 n.m. n.m. <0.1 Zimmer et al., 1998a
n.m., not measured; LA, lauric acid; MA, myristic acid; PA, palmitic acid; OA, oleic acid; DD, dodecane;
HD, hexadecane