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chapter 18
Lipids I: Fatty Acids and Eicosanoids
TABLE 18-4
Fatty Acid Composition o f Some Fats o f Animal and Plant Origin
Saturated*
C-14’ C16, C18
(predominantly C16 and C18)
Monounsaturated*
C16:l; 0 8 :1
(predominantly C18:l)
Polyunsaturated*,
mostly as linoleic
acid (0 8 :2 )
Animal Fats
Butter
59
37
4
Beef
54
44
2
Chicken
40
38
2 2
Pork
40
46
14
Fish (salmon and tuna)
28
29
23+20+
Vegetable Oils
Safflower
1 1
1 1
78
Corn
14
26
60
Sesame
14
43
43
Soybean
15
27
58
Peanut
2 0
45
35
Cottonseed
29
19
52
Coconut
92
6
2
Palm
53
37
1 0
Olive
16
69
15
Sunflower
1 2
18
70
* All values expressed as weight percentages of total fatty acids.
^ Other polyenoic acids, e.g., eicosapentaenoic acid, docosahexaenoic acid.
PGE,, PGF,,TXA,
LTA3, LTC,, LTD,
8,11,14-Eicosatrienoic acid
(dihomo- y-Iinolenic acid)
pdg2, pge2, pgf2, pgi2, txa2
^
lta4, ltb4, ltc4, ltd4, ltf4
5,8,11,14-Eicosatetraenoic acid
(arachidonic acid)
COOH
PGD„ PGE3, PGFj, PG1,, TXA,
^
LTAS
, LTBS
, LTC,
5,8,11,14,17-Eicosapentaenoic acid
FIGURE 18-17
Precursor and product relationships of eicosanoids: prostaglandins (PGs),
prostacyclins (PGIs), thromboxanes (TXs), and leukotrienes (LTs). Arrows
arising from each fatty acid indicate two different synthetic pathways: one
for prostanoids (PG, PGI, TX) and the other for leukotrienes. The
numerical subscript of an eicosanoid indicates the total number of double
bonds in the molecule and thus the series to which it belongs. The
prostanoids contain two fewer double bonds than does the precursor
fatty acid.
to stimuli requires mobilization of precursor fatty acids
bound by ester, ether, or amide linkages. This utilization
is generally considered the rate-limiting step. Membrane
phosphoglycerides contain essential fatty acids in the
2
-
position. In response to stimuli and after the activation of
the appropriate phospholipase, the essential fatty acid is
released.
Known phospholipases and their hydrolytic specifici-
ties are shown in Figure 18-18. The primary source of
Phospholipase A,
O
Phospholipase Aj
__
q — C
R
Ï
R,— C— O— Ç H
Phospholipase D
Predominantly
an essential
fatty acid
H2C—O'
O
II
P— O—
o
Phospholipase C
Serine
Ethanolamine
Choline
Inositol
FIGURE 18-18
Hydrolysis of phosphoglycerides by phospholipases, whose cleavage sites
are shown by vertical arrows.
