Food Lipids: Chemistry, Nutrition, and Biotechnology

Figure 1 Perioxisomal �-oxidation activation and pathway in plants: 1, acyl-CoA oxidase;
2, multifunctional protein (enoyl-CoA hydratase activity): 3, multifunctional protein (3-hydroxyacyl-CoA
dehydrogenase activity); 4, 3-oxo-acyl-CoA thiolase. Asterisk indicates activation
of 2-oxo acid catalyzed by oxidative decarboxylation. (Adapted from Ref. 41.)
a thiolytic step with CoA-SH to acetyl CoA and an acyl CoA containing two carbon
atoms less than the parent acyl CoA. The intermediates (acyl-CoA thioesters) of this
reaction sequence in higher plant peroxisomes are identical to those established for
the �-oxidation reaction sequence in mammalian mitochondria and in bacteria; however,
thus far except for the thiolytic cleavage step, the individual steps of the �oxidation
reaction sequence are catalyzed in plant peroxisomes by quite different
enzymes.
The first �-oxidation step of the plant peroxisomal �-oxidation reaction sequence
leading from acyl CoA to 2E-enoyl-CoA is an oxygen-dependent reaction.
Reaction products are H 2O 2 [7,19] and enoyl CoA [19]. The plant acyl-CoA oxidase
is a homodimer (M r 150 kDa), FAD-containing protein like the acyl-CoA oxidase
of mammalian and yeast peroxisomes [20]. The purified enzyme of glyoxysomes
from cucumber (Cucumis sativus L.) cotyledons preferentially acts on long chain
acyl CoAs. However, linoleoyl CoA and linolenoyl CoA are not as good substrates
as other long chain fatty acids [20]. The enzyme from spinach (Spinacia oleracea
Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.