1. FATTY ACID OCCURRENCE AND DISTRIBUTION
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lished with considerable certainty the constitution of the C 20 and C 22
polyenoic acids of human brain as the same as those shown in Table
XXXII for the glycerophospholipids of ox liver, except that eicos-8,11,
14,17-tetraenoic acid was not found, and the presence of docosapentaenoic acid was uncertain.
F. BLOOD LIPIDS
Information on blood lipids is rather meager. However, there are
data concerning the composition of lipids of ox blood.
The distribution of fatty acids shows wide differences in the different fractions. In both series the triglycerides resemble in their composition the depot fats (cf. Table XXXIII) although the first sample
contains an unusually high content of linoleic acid. The sterol esters
which form the greater part of the total lipids are entirely different in
composition. As mentioned in Section IV, they are notably rich in
linoleic and total unsaturated acids. Thus the distribution of fatty acids
in ox blood at least will differ from that of the main depot fats and tissues in the relatively higher content of linoleic and unsaturated acids
generally.
G. GENERAL CONCLUSIONS
In plants it is clear even from the limited data available that in the
different parts of plants there are different types of lipids. In the leaf,
waxes and phospholipids are important constituents, in addition to
galactolipids, whereas in the seeds the fatty acids are present very
largely as triglycerides. The seed fats are not necessarily related to the
leaf fats in their fatty acid composition. The predominant fatty acid of
rapeseed—erucic acid—does not occur in the leaf, and conversely
hexadeca-7,10,13-trienoic acid, a major constituent in the leaf galactolipids
is apparently absent from the seed fat. Similarly, comparisons between
fruit-coat and seed fats show that each part elaborates its own types
of fatty acids.
In animals fed a diet low in fat, the depot fats invariably consist of
25-30% palmitic acid, together with stearic acid, usually in lesser
amounts, and oleic acid. On the other hand the brain lipids as well as
those of the nonadipose tissues usually contain considerable proportions
of C 20 and C 22 highly unsaturated acids. These apparently arise from
the dietary linoleic and linolenic acids. However, as mentioned in Section V, the sphingolipids contain longer-chain acids of the C 24 and
C 26 series, including saturated, α-hydroxy substituted, and unsaturated
acids, which are presumably synthesized in the tissues and are characteristic of animal life. The fatty secretions of skin, hair, and preen
81
lished with considerable certainty the constitution of the C 20 and C 22
polyenoic acids of human brain as the same as those shown in Table
XXXII for the glycerophospholipids of ox liver, except that eicos-8,11,
14,17-tetraenoic acid was not found, and the presence of docosapentaenoic acid was uncertain.
F. BLOOD LIPIDS
Information on blood lipids is rather meager. However, there are
data concerning the composition of lipids of ox blood.
The distribution of fatty acids shows wide differences in the different fractions. In both series the triglycerides resemble in their composition the depot fats (cf. Table XXXIII) although the first sample
contains an unusually high content of linoleic acid. The sterol esters
which form the greater part of the total lipids are entirely different in
composition. As mentioned in Section IV, they are notably rich in
linoleic and total unsaturated acids. Thus the distribution of fatty acids
in ox blood at least will differ from that of the main depot fats and tissues in the relatively higher content of linoleic and unsaturated acids
generally.
G. GENERAL CONCLUSIONS
In plants it is clear even from the limited data available that in the
different parts of plants there are different types of lipids. In the leaf,
waxes and phospholipids are important constituents, in addition to
galactolipids, whereas in the seeds the fatty acids are present very
largely as triglycerides. The seed fats are not necessarily related to the
leaf fats in their fatty acid composition. The predominant fatty acid of
rapeseed—erucic acid—does not occur in the leaf, and conversely
hexadeca-7,10,13-trienoic acid, a major constituent in the leaf galactolipids
is apparently absent from the seed fat. Similarly, comparisons between
fruit-coat and seed fats show that each part elaborates its own types
of fatty acids.
In animals fed a diet low in fat, the depot fats invariably consist of
25-30% palmitic acid, together with stearic acid, usually in lesser
amounts, and oleic acid. On the other hand the brain lipids as well as
those of the nonadipose tissues usually contain considerable proportions
of C 20 and C 22 highly unsaturated acids. These apparently arise from
the dietary linoleic and linolenic acids. However, as mentioned in Section V, the sphingolipids contain longer-chain acids of the C 24 and
C 26 series, including saturated, α-hydroxy substituted, and unsaturated
acids, which are presumably synthesized in the tissues and are characteristic of animal life. The fatty secretions of skin, hair, and preen