2
F. B. SHORLAND
I. Introduction
In living tissues fatty acids are present in a variety of compounds.
These include mainly triglycerides, or true fats, and to a lesser extent
phospholipids, waxes, and sterol esters. Free fatty acids do not normally
occur in living tissues in more than trace amounts. The amounts of
fatty substances, or lipids, range from less than 1% in the bodies of certain fish to more than 50% in some seeds and in well-fattened farm animals. A few microorganisms, especially yeasts, when suitably cultured
produce much fat.
In animals the amount of fat or triglyceride is affected markedly by
the plane of nutrition whereas the amounts of cholesterol and of phospholipid remain approximately constant (J). To distinguish between
these two groups of lipids, Terroine (2) suggested the terms "element
variable" and "element constant."
A wide range of fatty acids is found in nature. The depot fats synthesized by animals consist chiefly of palmitic (25-30%), oleic, and
stearic acids. In addition, the dietary linoleic and linolenic acids of
plant origin are elongated and desaturated in the animal. In this way
are formed the characteristic polyenoic C 20 and C 22 unsaturated acids
not found in the ingested vegetable fats. The depot fats also include
considerable amounts of unmodified dietary fatty acids.
In ruminant fats the presence of positional and trans isomers of the
naturally occurring unsaturated acids is another deviation from the
simple mixtures of fatty acids characteristic of animal fats. Also in
ruminant fats occur minor or trace amounts of n-odd, iso, and
(+)-anteiso acids. These originate possibly from the lower homologs
arising from breakdown of carbohydrates and proteins in the rumen.
The fatty excretions of the skin, including wool grease, hair lipids,
and the preen gland lipids of birds, offer a somewhat more complex
pattern of fatty acid distribution. In some skin lipids occur abundant
amounts of branched-chain fatty acids as well as the n-odd series of
saturated and unsaturated fatty acids. In the lipids of microorganisms
and higher plants, the fatty acid mixtures may consist largely of oleic
and linoleic acids, sometimes with linolenic acid as the main unsaturated
component together with palmitic acid, which usually forms less than
10% of the total fatty acids. Frequently, however, unusual fatty acids
characteristic of the species also occur as major constituents. Thus, in
tubercle bacilli higher molecular weight branched-chain fatty acids
predominate. In the seed fats of the higher plants there are many examples of the occurrence of specific fatty acids. In the Umbelliferae,
petroselinic (octadec-m-6-enoic) acid largely replaces oleic acid, while
F. B. SHORLAND
I. Introduction
In living tissues fatty acids are present in a variety of compounds.
These include mainly triglycerides, or true fats, and to a lesser extent
phospholipids, waxes, and sterol esters. Free fatty acids do not normally
occur in living tissues in more than trace amounts. The amounts of
fatty substances, or lipids, range from less than 1% in the bodies of certain fish to more than 50% in some seeds and in well-fattened farm animals. A few microorganisms, especially yeasts, when suitably cultured
produce much fat.
In animals the amount of fat or triglyceride is affected markedly by
the plane of nutrition whereas the amounts of cholesterol and of phospholipid remain approximately constant (J). To distinguish between
these two groups of lipids, Terroine (2) suggested the terms "element
variable" and "element constant."
A wide range of fatty acids is found in nature. The depot fats synthesized by animals consist chiefly of palmitic (25-30%), oleic, and
stearic acids. In addition, the dietary linoleic and linolenic acids of
plant origin are elongated and desaturated in the animal. In this way
are formed the characteristic polyenoic C 20 and C 22 unsaturated acids
not found in the ingested vegetable fats. The depot fats also include
considerable amounts of unmodified dietary fatty acids.
In ruminant fats the presence of positional and trans isomers of the
naturally occurring unsaturated acids is another deviation from the
simple mixtures of fatty acids characteristic of animal fats. Also in
ruminant fats occur minor or trace amounts of n-odd, iso, and
(+)-anteiso acids. These originate possibly from the lower homologs
arising from breakdown of carbohydrates and proteins in the rumen.
The fatty excretions of the skin, including wool grease, hair lipids,
and the preen gland lipids of birds, offer a somewhat more complex
pattern of fatty acid distribution. In some skin lipids occur abundant
amounts of branched-chain fatty acids as well as the n-odd series of
saturated and unsaturated fatty acids. In the lipids of microorganisms
and higher plants, the fatty acid mixtures may consist largely of oleic
and linoleic acids, sometimes with linolenic acid as the main unsaturated
component together with palmitic acid, which usually forms less than
10% of the total fatty acids. Frequently, however, unusual fatty acids
characteristic of the species also occur as major constituents. Thus, in
tubercle bacilli higher molecular weight branched-chain fatty acids
predominate. In the seed fats of the higher plants there are many examples of the occurrence of specific fatty acids. In the Umbelliferae,
petroselinic (octadec-m-6-enoic) acid largely replaces oleic acid, while