22
F. B. SHORLAND
thus evidence of enzyme selectivity during synthesis of these lipids or of
subsequent acyl interchange.
2. Exogenous Fat
There are many experiments to show that the dietary fat exerts a
profound influence on the composition of the depot fats. In extreme
cases when the diet includes considerable proportions of fat, the fatty
acid composition of the dietary fat and the depot fat may be almost
indistinguishable, as shown in Table II. Thus rats fed corn oil deposit
fat containing similar proportions of fatty acids to those found in the
diet.
Sometimes there are complicating factors so that the effect of the
dietary fat is not so obvious as is illustrated by the fatty acid composition of the depot fats of rats fed coconut oil (see Table II). The lower
fatty acids are here shown to be preferentially metabolized. In general
it is found that the lower fatty acids (below Ci 2 ) are not stored in the
depot fats of animals. However, dietary octanoic and decanoic acids are
stored in the skin of rats (115).
Although the concept of the dynamic state (116) has been applied
to the endogenous fatty acids of depot fats, it appears that the dietary
fatty acids that are not formed endogenously, including linoleic, linolenic, and highly unsaturated C 2 o-C 2 2 acids, are not readily mobilized
and tend to remain in the depot fats after withdrawal from the diet
[cf. Longenecker (113)]. Dietary (+)-14-methylhexadecanoic acid
similarly persists in rat depot fats after withdrawal from the diet (117).
In ruminants the dietary unsaturated acids are hydrogenated in the
rumen (118-120) with the result that these acids, notably linoleic and
linolenic, are not found to any appreciable extent in the depot fats, but
are largely converted to stearic acid and to eis and trans positional
isomers of oleic acid (121).
C. SYNTHESIS OF FATS IN HIGHER PLANTS
The wider range of fatty acids in lipids of higher plants suggests
that there must be available mechanisms for synthesis in addition to
those found in animals. It appears that, like the higher animals, the
higher plants transform carbohydrates and possibly proteins into fats,
though the experimental evidence is perhaps less definite than might
be desired.
The earlier studies on fat metabolism in plants, which have been
reviewed by Hilditch (3), show that during the ripening of seeds there
is a decrease in carbohydrate content accompanied by an increase in
F. B. SHORLAND
thus evidence of enzyme selectivity during synthesis of these lipids or of
subsequent acyl interchange.
2. Exogenous Fat
There are many experiments to show that the dietary fat exerts a
profound influence on the composition of the depot fats. In extreme
cases when the diet includes considerable proportions of fat, the fatty
acid composition of the dietary fat and the depot fat may be almost
indistinguishable, as shown in Table II. Thus rats fed corn oil deposit
fat containing similar proportions of fatty acids to those found in the
diet.
Sometimes there are complicating factors so that the effect of the
dietary fat is not so obvious as is illustrated by the fatty acid composition of the depot fats of rats fed coconut oil (see Table II). The lower
fatty acids are here shown to be preferentially metabolized. In general
it is found that the lower fatty acids (below Ci 2 ) are not stored in the
depot fats of animals. However, dietary octanoic and decanoic acids are
stored in the skin of rats (115).
Although the concept of the dynamic state (116) has been applied
to the endogenous fatty acids of depot fats, it appears that the dietary
fatty acids that are not formed endogenously, including linoleic, linolenic, and highly unsaturated C 2 o-C 2 2 acids, are not readily mobilized
and tend to remain in the depot fats after withdrawal from the diet
[cf. Longenecker (113)]. Dietary (+)-14-methylhexadecanoic acid
similarly persists in rat depot fats after withdrawal from the diet (117).
In ruminants the dietary unsaturated acids are hydrogenated in the
rumen (118-120) with the result that these acids, notably linoleic and
linolenic, are not found to any appreciable extent in the depot fats, but
are largely converted to stearic acid and to eis and trans positional
isomers of oleic acid (121).
C. SYNTHESIS OF FATS IN HIGHER PLANTS
The wider range of fatty acids in lipids of higher plants suggests
that there must be available mechanisms for synthesis in addition to
those found in animals. It appears that, like the higher animals, the
higher plants transform carbohydrates and possibly proteins into fats,
though the experimental evidence is perhaps less definite than might
be desired.
The earlier studies on fat metabolism in plants, which have been
reviewed by Hilditch (3), show that during the ripening of seeds there
is a decrease in carbohydrate content accompanied by an increase in