1. FATTY ACID OCCURRENCE AND DISTRIBUTION
55
these acids in the plasma and liver cholesterol esters are somewhat
reduced (279). The fatty acid distribution in cholesterol esters is thus
entirely different from that of the glycerides and phospholipids, which
contain palmitic and oleic acids as the main constituents. In the flesh
of the haddock cholesterol esters have also been found to be notably
rich in highly unsaturated fatty acids as compared with those present
in other lipids (280).
B. FATTY ACIDS OF PHOSPHOLIPIDS
In connection with these studies, most of the work on the types of
fatty acids has been on phospholipid fractions separated as a rule from
the corresponding glycerides by precipitation in acetone solution. Individual phospholipid species have also been investigated, but it is
possible in some instances that the preparations are not representative
of the particular phospholipid as it naturally occurs. The available
methods of purification tend to remove or to select a fraction containing
one type of fatty acid in preference to another.
1. Phospholipids of Animals
It will be seen from Table XV that the fatty acid composition of the
phospholipids of various species follows a similar pattern and that, as
compared with depot fats, differences in fatty acid composition between the phospholipids of aquatic species and those of higher land
mammals are much less marked. The highly unsaturated C 20 to C 22 acids
characteristic of fish depot fats are present only in slightly lower proportions in the phospholipids of higher land mammals as compared with
fish. As earlier mentioned, however, the highly unsaturated acids of
aquatic life are mainly of the linolenic type, whereas those of the
higher land mammals are mainly of the linoleic type (41).
In fish the fatty acid composition of the corresponding phospholipids
and glycerides is similar. In the higher land animals, however, the
phospholipids, as compared with the corresponding glycerides (see
Tables III and XV), have more of the higher molecular weight fatty
acids, including especially the C 20 and C 22 highly unsaturated acids, but
less palmitic and hexadecenoic acids. In particular the liver phospholipids, as compared with the depot fats, show rather pronounced differences as the latter have not more than traces of C 20 and C 22 highly
unsaturated acids.
The main points of difference between the liver phospholipids, liver
glycerides, and depot fats of the higher land mammals may be illustrated
by consideration of the fatty acid composition of the horse lipids (183).
In addition to the differences shown in Table XVI very marked
55
these acids in the plasma and liver cholesterol esters are somewhat
reduced (279). The fatty acid distribution in cholesterol esters is thus
entirely different from that of the glycerides and phospholipids, which
contain palmitic and oleic acids as the main constituents. In the flesh
of the haddock cholesterol esters have also been found to be notably
rich in highly unsaturated fatty acids as compared with those present
in other lipids (280).
B. FATTY ACIDS OF PHOSPHOLIPIDS
In connection with these studies, most of the work on the types of
fatty acids has been on phospholipid fractions separated as a rule from
the corresponding glycerides by precipitation in acetone solution. Individual phospholipid species have also been investigated, but it is
possible in some instances that the preparations are not representative
of the particular phospholipid as it naturally occurs. The available
methods of purification tend to remove or to select a fraction containing
one type of fatty acid in preference to another.
1. Phospholipids of Animals
It will be seen from Table XV that the fatty acid composition of the
phospholipids of various species follows a similar pattern and that, as
compared with depot fats, differences in fatty acid composition between the phospholipids of aquatic species and those of higher land
mammals are much less marked. The highly unsaturated C 20 to C 22 acids
characteristic of fish depot fats are present only in slightly lower proportions in the phospholipids of higher land mammals as compared with
fish. As earlier mentioned, however, the highly unsaturated acids of
aquatic life are mainly of the linolenic type, whereas those of the
higher land mammals are mainly of the linoleic type (41).
In fish the fatty acid composition of the corresponding phospholipids
and glycerides is similar. In the higher land animals, however, the
phospholipids, as compared with the corresponding glycerides (see
Tables III and XV), have more of the higher molecular weight fatty
acids, including especially the C 20 and C 22 highly unsaturated acids, but
less palmitic and hexadecenoic acids. In particular the liver phospholipids, as compared with the depot fats, show rather pronounced differences as the latter have not more than traces of C 20 and C 22 highly
unsaturated acids.
The main points of difference between the liver phospholipids, liver
glycerides, and depot fats of the higher land mammals may be illustrated
by consideration of the fatty acid composition of the horse lipids (183).
In addition to the differences shown in Table XVI very marked