Biology Reference
In-Depth Information
fatty acids including
a
-linolenic, EPA, and DHA must be primarily obtained from the diet.
The long chain omega-3 fatty acids EPA and DHA are often obtained from fish, such as
salmon, tuna, and halibut, and other marine life including algae and krill
[15]
.Theshorter
chain omega-3,
a
-linolenic acid, is a common component of plants that in man is only inef-
ficiently converted to the longer chain omega-3s by chain desaturation before the
9posi-
tion followed by chain elongation. Although rarely found in plants, arachidonic acid (AA,
20:4
6
5,8,11,14
) is the most abundant of the omega-6 series in animals. In man AA is a major
component of membranes and is the principal precursor of eicosanoids including the pros-
taglandins, isoprostanes, and isofurans. It is believed that the omega-6/omega-3 ratio is
prognostic of human health. Ideally this ratio should be between 1:1 to 4:1, but in the Amer-
ican diet this ratio is currently between 10:1 to 30:1, resulting in high cardiovascular disease.
6
Most Abundant Membrane Fatty Acids
The fatty acids most commonly found in mammalian membranes are: palmitic (16:0), stea-
ric (18:0), palmitoleic (16:1), oleic (18:1), linoleic (18:2), arachidonic (20:4), and docosahexae-
noic (22:6).
Table 4.8
presents a 'typical' mammalian membrane fatty acid composition profile
[16]
. The presented fatty acid compositions are of phosphatidylcholine (PC) isolated from rat
liver membranes. Fatty acids are expressed as weight percent.
Trans Fatty Acids
Although far less common, some trans (also designated E) double bonds are routinely
found in human membranes
[17]
. They enter the diet through dairy products, meat, and
partially hydrogenated plant oils and are suspected to disrupt normal membrane functions.
Although trans fatty acids are missing in plant lipids, they are present in animal fats, partic-
ularly those of ruminants. The most common trans fatty acid found in man is elaidic acid
(18:1
6
9t
). However, a bewildering array of
trans
fatty acids is produced as byproducts of
TABLE 4.8
Fatty Acid Composition of Phosphatidylcholine (PC) Isolated from Rat Liver Membranes.
The Data was Taken from
[16]
.
Membrane
Fatty acid
14:0
16:0
16:1
18:0
18:1
18:2
18:3
20:4
22:6
Rat Liver
0.5
29.7
1.0
16.8
10.4
16.8
18.3
3.4
Mito (outer)
0.4
27.0
4.1
21.0
13.5
13.5
15.7
3.5
Mito (inner)
0.3
27.1
3.6
18.0
16.2
15.8
18.5
3.8
Plasma Membrane
0.9
36.9
31.2
6.4
12.9
tr
11.1
SER
0.4
28.6
3.1
26.5
10.6
14.9
14.0
0.7
RER
0.5
22.7
3.6
22.0
11.1
16.1
19.7
2.9
Golgi
0.9
34.7
22.5
8.7
18.1
tr
14.5
