Fatty acid oxidation is an important pathway for energy production
in mammals and birds. In animal tissues the enzymes of fatty
acid oxidation are located in the mitochondrion. Recent reports
suggest that this is not the case in Castor bean endosperm. In this
tissue the enzymes of B-oxidation are localized in a very fragile cell
organelle, called the glyoxysomes .
Fatty acids are transported in the blood complexed to albumin,
or in esterified form as triglycerides and phospholipids,
complexed to protein (lipoproteins). Lipoproteins are synthesized
in the liverand in the intestinal epithelium (chylomicrons). Before
entering the cell these triglycerides are generally hydrolyzed by lipoprotein
lipase, an enzyme activated by heparin and probably present
in the endothelial cells of the capillary wall.
From the foregoing it is evident that fatty acid presented to the
cell for further metabolism is in the form of "free" fatty acid.
Fatty acids cannot participate in any reaction of intermediary
metabolism, before they have been "activated" to their thioester
with CoA. This reaction is necessary for triglyceride and phospholipid
biosynthesis, for acyl interchange between complex lipids, for
chain-elongation reactions and also for oxidative degradation of fatty
acids