Membrane Lipids: Fatty Acids - An Introduction to Biological Membranes - page 49

TABLE 4.6 The Most Important Monoenoic Fatty Acids Found in Membranes [9] .

Melting Point ( o C)

Systematic Name Trivial Name Structure

cis-9-hexadecenoic palmitoleic 16:1(n-7) 0.5

cis-6-octadecanoic petroselinic 18:1(n-12) 30

cis-9-octadecanoic oleic 18:1(n-9) 16.2

trans-9-octadecanoic elaidic 18:1(n-9) 43.7

cis-11-octadecanoic vaccenic 18:1(n-7) 39

cis-11-eicosenoic gadoleic 20:1(n-9) 25

cis-13-docosenoic erucic 22:1(n-9) 33.4

cis-15-tetracosenoic nervonic 24:1(n-9) 39

Monoenoic Fatty Acids
The monoenoic fatty acid (MUFA), oleic acid, was also discovered by Chevreul in his pio-
neering studies on pork fat in 1823 [10] . Now over 100 monoene fatty acids are known. The
most important monoenoic fatty acids found in membranes are listed in Table 4.6 with their
corresponding melting point (T m ). The omega designation is referred to as n and is discussed
below. It is evident in comparing the T m s that saturated fatty acids of the same chain length
have much higher T m s than do fatty acids with one double bond. For example, stearic acid
(18:0) has a melting point of 69.6 o C while oleic acid (18:1 6 9 ) is 16.2 o C.

Polyenoic Fatty Acids
All polyenoic fatty acids (PUFAs) have very low melting points ( Table 4.7 ) and are highly
susceptible to oxidative degradation (peroxidation) [11] . UV radiation, high temperature,
oxygen, metals, and alkaline conditions are sufficient to alter these molecules by enhancing
not only oxidation but also double bond migration and isomerization, resulting in a multi-
tude of complex positional geometric isomers. Positional isomerization can occur in PUFAs

TABLE 4.7 Most Important Membrane Polyenoic Fatty Acids [11] .

Melting Point ( o C) Systematic Name Trivial Name Structure

9,12-octadecadienoic linoleic 18:2(n-6) 5

6,9,12-octadecatrienoic g -linolenic 18:3(n-6)

9,12,15-octadecatrienoic a -linolenic 18:3(n-3) 11

5,8,11,14-eicosatetraenoic arachidonic 20:4(n-6) 50

5,8,11,14,17-eicosapentaenoic EPA 20:5(n-3) 54

7,10,13,16,19-docosapentaenoic DPA 22:5(n-3)

4,7,10,13,16,19-docosahexaenoic DHA 22:6(n-3) 44