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Food Lipids: Chemistry, Nutrition, and Biotechnology

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Figure 2 The glyoxylate cycle in glyoxysome <strong>and</strong> the pathway of conversion of fatty acid<br />

to sucrose in the germinating oilseeds: 1, fatty acyl-CoA ligase; 2, �-oxidation; 3, citrate<br />

synthetase; 4, aconitase; 5, isocitrate lyase; 6, malate synthetase; 7, malate dehydrogenase;<br />

PEP, phosphoenolpyruvate; PGA, 3-phosphoglycerate; DiPGA, 1,3-diphosphoglycerate; FBP,<br />

fructose-1,6-bisphosphate. (Adapted from Ref. 11.)<br />

dation represents the classic �-oxidation system. Mammalian peroxisomal �-oxidation<br />

attacks only very long chain fatty acids, <strong>and</strong> the sequence ends at octanoyl CoA.<br />

In the higher plant cells, however peroxisomes completely catabolize physiologically<br />

relevant fatty acids [20]. This finding has led researchers to ask whether higher plant<br />

cells possess an additional, mitochondrial �-oxidation system. The evidence appears<br />

to be controversial.<br />

Experimental results that favor mitochondrial �-oxidation include the following:<br />

1. Plant mitochondria contain L-carnitine [34,35] <strong>and</strong> carnitine acyltransferase<br />

activity [36,37]. Carnitine acyltransferase activity has been detected using<br />

long, medium <strong>and</strong> short chain acyl CoAs as substrate. The enzyme reacting<br />

with long chain acyl CoAs is thought to be involved in mitochondrial �oxidation<br />

[38], being both associated with the outer face of the inner membrane<br />

of pea cotyledon mitochondria, as well as localized intramitochondrially<br />

[39].<br />

2. Mitochondrial �-oxidation in animal cells is KCN-sensitive, since an acyl-<br />

CoA dehydrogenase tightly coupled to the respiratory chain catalyzes the<br />

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

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