6
F. B. SHORLAND
the classification of species is far from complete. The interpretation of
our present knowledge requires an understanding of the metabolism of
fatty acids and especially of their biosynthesis. Even in this field there
are wide gaps and the formation of the unusual types of fatty acids
found in some plants and microorganisms remains unexplained.
II. The Naturally Occurring Fatty Acids and Lipids
A. TYPES OF NATURALLY OCCURRING FATTY ACIDS
The naturally occurring fatty acids may be divided into: (i)
n-saturated acids; (ii) n-unsaturated acids; (iii) branched-chain acids;
and (iv) cyclic acids.
1. n-Saturated Fatty Acids
The n-even-numbered acids from C 2 to C 26 , inclusive, occur in natural fats, the most abundant being palmitic (Ci 6 ) acid. The higher
members up to C 36 are found in waxes. The presence of n-odd-numbered
acids in certain animal (16-18) and plant fats (19, 20) has only recently been satisfactorily established. All members of the series from
C 3 to C 25 have been isolated or detected. Substituted n-saturated acids
are not commonly found in nature. However, optically active 2-hydroxy
n-even-numbered acids from C i2 to Ci 8 together with 2-hydroxy-16methylheptadecanoic acid have been isolated from wool wax (21), and
the C 24 and C 26 homologs occur in brain lipids (22). In addition,
ω-hydroxy acids (C 18 to C 30 ) have been isolated from carnauba wax
(23).
2. n-Umaturated Fatty Acids
The unsaturated fatty acids are classified as: (a) monoethenoid, (b)
diethenoid, (c) triethenoid, (d) polyethenoid, and (e) acetylenic acids.
The double bonds of the naturally occurring fatty acids usually possess
the eis configuration.
a. Monoethenoid Acids. Oleic (octadec-ds-9-enoic) acid is the most
common of all fatty acids, but in the seed oils of the Umbelliferae it is
largely replaced by petroselinic (octadec-m-6-enoic) acid; and in
lactobacilli, cis-vaccenic (octadec-cis-11-enoic) acid, but not oleic acid,
is found (24). Other commonly occurring monoethenoid acids include
palmitoleic (hexadec-cis-9-enoic) acid. Erucic (docos-cis-13-enoic)
acid occurs in quantity in the seed fats of the Cruciferae. Ricinoleic
(12-hydroxyoctadec-ds-9-enoic) acid is the best-known long-chain
hydroxy acid, being present in high proportions (90%) in castor oil.
9-Hydroxyoctadec-12-enoic acid is present in the seed oils of Strophan-
F. B. SHORLAND
the classification of species is far from complete. The interpretation of
our present knowledge requires an understanding of the metabolism of
fatty acids and especially of their biosynthesis. Even in this field there
are wide gaps and the formation of the unusual types of fatty acids
found in some plants and microorganisms remains unexplained.
II. The Naturally Occurring Fatty Acids and Lipids
A. TYPES OF NATURALLY OCCURRING FATTY ACIDS
The naturally occurring fatty acids may be divided into: (i)
n-saturated acids; (ii) n-unsaturated acids; (iii) branched-chain acids;
and (iv) cyclic acids.
1. n-Saturated Fatty Acids
The n-even-numbered acids from C 2 to C 26 , inclusive, occur in natural fats, the most abundant being palmitic (Ci 6 ) acid. The higher
members up to C 36 are found in waxes. The presence of n-odd-numbered
acids in certain animal (16-18) and plant fats (19, 20) has only recently been satisfactorily established. All members of the series from
C 3 to C 25 have been isolated or detected. Substituted n-saturated acids
are not commonly found in nature. However, optically active 2-hydroxy
n-even-numbered acids from C i2 to Ci 8 together with 2-hydroxy-16methylheptadecanoic acid have been isolated from wool wax (21), and
the C 24 and C 26 homologs occur in brain lipids (22). In addition,
ω-hydroxy acids (C 18 to C 30 ) have been isolated from carnauba wax
(23).
2. n-Umaturated Fatty Acids
The unsaturated fatty acids are classified as: (a) monoethenoid, (b)
diethenoid, (c) triethenoid, (d) polyethenoid, and (e) acetylenic acids.
The double bonds of the naturally occurring fatty acids usually possess
the eis configuration.
a. Monoethenoid Acids. Oleic (octadec-ds-9-enoic) acid is the most
common of all fatty acids, but in the seed oils of the Umbelliferae it is
largely replaced by petroselinic (octadec-m-6-enoic) acid; and in
lactobacilli, cis-vaccenic (octadec-cis-11-enoic) acid, but not oleic acid,
is found (24). Other commonly occurring monoethenoid acids include
palmitoleic (hexadec-cis-9-enoic) acid. Erucic (docos-cis-13-enoic)
acid occurs in quantity in the seed fats of the Cruciferae. Ricinoleic
(12-hydroxyoctadec-ds-9-enoic) acid is the best-known long-chain
hydroxy acid, being present in high proportions (90%) in castor oil.
9-Hydroxyoctadec-12-enoic acid is present in the seed oils of Strophan-