Food Lipids: Chemistry, Nutrition, and Biotechnology

long chain fatty acids with a cis double bond in the C-9 position (see below) (116).
Other lipases that show some preference for specific fatty acids are those from C.
rugosa (C18:1 cis-9), strains of A. niger (C10 and C12 or C18:1 cis-9), M. miehei
(C12), Rhizopus arrhizus (C8, C10) (115), Humicola lanuginosa #3 (117), and human
gastric lipase (C8 and C10) (118). A lipase from Penicillium camembertii hydrolyzes
only mono- and diacylglycerols (119).
Negative selectivity has been observed where the lipase from C. cylindracea
(rugosa) selected against triacylglycerol molecules containing DHA (120); G. candidum
lipase preparations have shown similar discrimination for �-linolenate in
borage oil (121), and erucic acid from rapeseed oil (122).
Lipase selectivity/specificity may be due to structural features of the substrate
(e.g., fatty acid chain length, unsaturation, stereochemistry), physicochemical factors
at the interface, and/or differences in the binding sites of the enzyme. Stereoselectivity
of enzymes can be influenced by temperature and hydrophobicity of the solvent.
Recently, Rogalska et al. (123) showed that the enantioselectivity of lipases
from R. miehei, C. antarctica B, lipoprotein lipase, and human gastric lipase toward
monolayers of racemic dicaprin was enhanced at low surface pressures, while catalytic
activity decreased.
Variations in specificity of lipase preparations from different fungi, different
strains of the same species, and the same strain cultured under different conditions
may be due to the production of multiple isoforms with differing specificities (124).
The lipase(s) of G. candidum have been of particular interest because those from
some strains exhibit a relatively high preference for ester bonds involving fatty acids
with a cis-9 double bond (e.g., oleic acid). Geotrichum species and strains produce
at least two glycosylated lipases, most often designated lipase I and II, or less often
A or B, which are coded for by two genes (13,14,96,125). Additional isoforms may
be produced that differ by degrees of glycosylation. There are conflicting reports on
the specificities of the two lipases. For example, of the two lipases produced by G.
candidum CMICC 335426, lipase B showed high showed high specificity for the
cis-9 unsaturates whereas lipase A of this strain and, according to Sidebottom et al.
(15), lipases I and II of ATCC 34614, showed no preference. Bertolini et al. (125)
recently cloned lipases I and II from G. candidum ATCC 34614 into Saccharomyces
cerevisiae, then isolated and purified the two lipases from this yeast and determined
their substrate specificities. Lipase I showed higher specificity than lipase II for long
chain unsaturated fatty acyl chains with cis-9 double bond, and lipase II showed a
preference for substrates having short acyl chains (C 8 to C 14). These investigators
also showed that sequence variation in the N-terminal amino acids of these lipases,
or the lid, does not contribute to variation in substrate preference. Not all strains of
G. candidum exhibit the preference for unsaturated fatty acids (11). The specificities
of isoforms of lipases from Geotrichum are shown in Table 3 (15,126–129).
Cygler et al. (105) suggested that the basis for the selectivity differences between
lipases I and II from G. candidum involves key amino acid residues along the
internal cavity presumed to be the binding site of the scissile acyl chain and that
selectivity does not involve the lid. Studies with a cloned lipase from R. delemar
(130) appear to support this suggestion. For example, substitution of certain amino
acids (e.g., Phe 95 → Asp) through site-directed mutagenesis in the substrate-binding
region resulted in an almost twofold increase in the preference for tricaprylin relative
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