where (Ac1X) and (Ac2X) are concentrations of the two substrates at time X andais
the competitive factor which is defined by the following equation:
a¼(VAc1X/KAc1X)/(VAc2X/KAc2X)
whereVis the maximal velocity andKis the Michaelis constant. The competitive
factor is calculated from the substrate concentrations Ac1X0 and Ac2X0 at time zero
as follows:
a¼Log[Ac1X0/Ac1X]/Log[Ac2X0/Ac2X].
Specificity constant is calculated from the competitive factor as 1/awith reference to
the specificity constant of the reference standard, e.g., myristic or oleic acid, taken as
1.00. The higher the specificity constant for a particular fatty acid, the higher is the
preference of the lipase for that particular fatty acid as substrate. Figure 2 shows the
specificity constants for common and unusual fatty acids in the esterification withn-
butanol, catalyzed by lipases from a mammalian tissue (porcine pancreas), plant
(rapeseed,Brassica napus) and microorganisms (Rhizomucor miehei,Rhizopus ar-
rhizusandCandida cylindracea¼C. rugosa). Despite being of different origin,
some common features of substrate specificities of these lipases are evident from
Figure 2.
Table 1 summarizes the fatty acid selectivity of triacylglycerol lipases from var-
ious sources. Lipases fromC. rugosa, R. miehei, R. arrhizus(Mukherjee et al., 1993;
Jachmania ́n et al., 1996; Figure 2),Penicillium cyclopiumandPenicilliumsp. (Li-
pase G) (Mukherjee et al., 1993) and those from germinating rapeseed (Hills et al.,
1990a; Jachmania ́n et al., 1996; Figure 2), papaya (Carica papaya) latex (Mukherjee
and Kiewitt, 1996b) and bromelain as well asRhizopussp. (Mukherjee and Kiewitt,
1998) have closely resembling substrate specificities in esterification withn-butanol.
All these lipases strongly discriminate against unsaturated fatty acids having the first
double bond from the carboxyl end at an even number carbon, i.e.cis-4, e.g. all-cis-
4,7,10,13,16,19-docosahexaenoic (n-3 22 : 6),cis-6, e.g.c-linolenic (all-cis-6,9,12-
octadecatrienoic, n-6 18 : 3), petroselinic (cis-6-octadecenoic,cis-6-18 : 1) and stear-
idonic (all-cis-6,9,12,15-octadecatetraenoic, n-3 18 : 4) orcis-8, e.g. dihomo-c-lino-
lenic (all-cis-8,11,14-eicosatrienoic, n-6 20 : 3) acid.
The selectivity of the lipase from porcine pancreas towards fatty acids having a
cis-4,cis-6 andcis-8 double bond is, however, not as pronounced as the correspond-
ing selectivities of the above lipases (Mukherjee et al., 1993; Jachmania ́n et al., 1996;
Figure 2).
The lipase fromChromobacterium viscosumexhibits different substrate specifi-
city compared to the above lipase preparations. This lipase utilizes fatty acids with a
cis-6 double bond, e.g.,cis-6-18 : 1, n-6 18 : 3 and n-3 18 : 4, as substrates equally
well or even better than myristic acid ora-linolenic acid (n-3 18 : 3) (Mukherjee et
al., 1993).
In interesterification reactions, lipase fromR. mieheidiscriminates againstcis-6–
18 : 1 (Osterberg et al., 1989), n-6 18 : 3 (Rangheard et al., 1989; Osterberg et al.,
1989) and n-3 22 : 6 (Langholz et al., 1989). Lipases fromC. rugosa, porcine pan-
creas andGeotrichum candidumalso discriminate against n-6 18 : 3 in interesteri-
2.2 Fractionation of fatty acids and other lipids by lipase-catalyzed reactions 25
