86
F. B. SHORLAND
and C 22 series are important constituents. They are usually based on
the pattern of linolenic acid with the first double bond in position 3
with respect to the CH 3 group. There are up to five double bonds in the
C 20 series and up to six double bonds in the C 22 series, each double
bond being separated from the next by a single methylenic group.
Somewhat similar C 20 and C 22 acids, based mainly on the linoleic pattern, are found in the nonadipose tissue glycerides and phospholipids of
land mammals (41). In addition, in ruminants the microorganisms in
the rumen hydrogenate the dietary linoleic and linolenic acids, giving
rise to mono- and to a lesser extent diethenoid acids which are trans
and positional isomers of oleic and linoleic acids (121).
Although as indicated above, oleic and linoleic acids are the main
fatty acids in plant fats, nevertheless the occurrence, in addition, of a
great diversity of unsaturated acids, makes it desirable to examine their
nature more closely.
In the monoethenoid series Hilditch (348) has shown that many of
the naturally occurring acids have a structure identical with one or
other half of oleic acid, i.e., CH 3 (CH 2 ) 7 CH= or =CH-(CH 2 ) 7 -COOH.
A well-known example is that of erucic (docos-13-enoic) acid, which
is present in quantity in the seed fats of the Cruciferae and Tropaeolaceae. In three species of the genus Ximenia of the Olacaceae family
the monoethenoid C 20 , C 22 , C 24 , C 26 , C 28 , and C 30 acids belonging to the
series CH 3 (CH 2 ) 7 CH=CH (CH 2 ) M COOH have been isolated and
found to comprise in all 25-33% of the total fatty acids (266). These
features, together with the occurrence of ximenynic (octadec-ll-en-9ynoic) acid, provide a unique fatty acid composition.
In the seed fats of the Umbelliferae, petroselinic (octadec-6-enoic)
acids shows a deviation in structure from the oleic type. This serves to
characterize the Umbelliferous species in which petroselinic acid invariably occurs.
A further deviation is that of the occurrence of cis-vaccenic (octadec-11-enoic) acid as the main unsaturated acid of certain bacterial
lipids including those of Lactobacillus, Streptococcus hemolyticus, and
Agrobacterium tumefaciens (206, 207).
The nonconjugated dienoic acids are represented by linoleic (octadeca-9,12-dienoic) acid. Apart from the minor amounts of the dienoic
acids in ruminant fats, the only other nonconjugated dienoic acid found
in substantial amounts is hexacosa-17,20-dienoic acid, which occurs in
the lipids of the sponge Spheciospongia vesparia (155). In addition
may be mentioned the conjugated dienoic acid, deca-2,4-dienoic acid
(29) and dodeca-2,4-dienoic acid (247), found in two species of
Euphorbiaceae.
F. B. SHORLAND
and C 22 series are important constituents. They are usually based on
the pattern of linolenic acid with the first double bond in position 3
with respect to the CH 3 group. There are up to five double bonds in the
C 20 series and up to six double bonds in the C 22 series, each double
bond being separated from the next by a single methylenic group.
Somewhat similar C 20 and C 22 acids, based mainly on the linoleic pattern, are found in the nonadipose tissue glycerides and phospholipids of
land mammals (41). In addition, in ruminants the microorganisms in
the rumen hydrogenate the dietary linoleic and linolenic acids, giving
rise to mono- and to a lesser extent diethenoid acids which are trans
and positional isomers of oleic and linoleic acids (121).
Although as indicated above, oleic and linoleic acids are the main
fatty acids in plant fats, nevertheless the occurrence, in addition, of a
great diversity of unsaturated acids, makes it desirable to examine their
nature more closely.
In the monoethenoid series Hilditch (348) has shown that many of
the naturally occurring acids have a structure identical with one or
other half of oleic acid, i.e., CH 3 (CH 2 ) 7 CH= or =CH-(CH 2 ) 7 -COOH.
A well-known example is that of erucic (docos-13-enoic) acid, which
is present in quantity in the seed fats of the Cruciferae and Tropaeolaceae. In three species of the genus Ximenia of the Olacaceae family
the monoethenoid C 20 , C 22 , C 24 , C 26 , C 28 , and C 30 acids belonging to the
series CH 3 (CH 2 ) 7 CH=CH (CH 2 ) M COOH have been isolated and
found to comprise in all 25-33% of the total fatty acids (266). These
features, together with the occurrence of ximenynic (octadec-ll-en-9ynoic) acid, provide a unique fatty acid composition.
In the seed fats of the Umbelliferae, petroselinic (octadec-6-enoic)
acids shows a deviation in structure from the oleic type. This serves to
characterize the Umbelliferous species in which petroselinic acid invariably occurs.
A further deviation is that of the occurrence of cis-vaccenic (octadec-11-enoic) acid as the main unsaturated acid of certain bacterial
lipids including those of Lactobacillus, Streptococcus hemolyticus, and
Agrobacterium tumefaciens (206, 207).
The nonconjugated dienoic acids are represented by linoleic (octadeca-9,12-dienoic) acid. Apart from the minor amounts of the dienoic
acids in ruminant fats, the only other nonconjugated dienoic acid found
in substantial amounts is hexacosa-17,20-dienoic acid, which occurs in
the lipids of the sponge Spheciospongia vesparia (155). In addition
may be mentioned the conjugated dienoic acid, deca-2,4-dienoic acid
(29) and dodeca-2,4-dienoic acid (247), found in two species of
Euphorbiaceae.