10
F. B. SHORLAND
Simple lipids include fats, or triglycerides, and waxes. Fats are esters
of glycerol and higher fatty acids, and waxes are esters of higher fatty
alcohols and higher fatty acids. In this category may be included also
sterol esters and vitamin A esters. Compound lipids contain other groups
in addition to the alcohol, and in the subdivision of compound lipids
there are various schemes and terminologies. The present author feels
that the terms simple and compound do not serve any useful purpose
in the classification of lipids and prefers to follow subdivisions based
on the type of derivation as follows: (i) esters of glycerol (fats or
triglycerides); (ii) esters of long-chain fatty alcohols and sterols
(waxes); (iii) esters of glycerophosphoric acid coupled with a nitrogen
base and/or a carbohydrate (phospholipids), and (iv) derivatives of
the long-chain hydroxyamino alcohol sphingosine (sphingolipids).
1. Fats
These, as already indicated, are esters (II) of glycerol and higher
fatty acids
CH 2 · O · CO · Ri
CH · O · CO · R 2
I
CH 2 · O · CO · R 3
(Π)
where R 1? R 2 , and R 3 are fatty acid radicals.
Living tissues contain little or no free fatty acid, and the glycerides
present are triglycerides. However, monoglycerides occur in the hog
pancreas (58). The naturally occurring fats as isolated are not purely
triglycerides but contain unsaponifiable matter, including sterols, hydrocarbons, and alcohols. Related to the fats or triglycerides are the fatty
esters of the a-glyceryl ethers of n-octadec-9-enyl (selachyl), n-octadecyl
(batyl), and n-hexadecyl (chimyl) alcohols.
In natural fats the wide variety of fatty acids permits numerous
combinations within the glyceride molecule. According to the views of
Hilditch (3), no simple triglyceride is formed if any other combination
is possible. This is the rule of even distribution, which, according to
Hilditch, applies to most fats, although not with mathematical precision. To account for the relatively high content of fully saturated
glycerides in many stearic acid-rich animal fats, Hilditch suggested
that such fats are assembled on an even-distribution basis but are
later modified in the animal by hydrogenation (3).
Other workers have suggested that a random (59, 60) or a restrictedrandom (61) distribution operates. The evidence shows that the fatty
acids are widely distributed among the glyceride molecules, but it is
F. B. SHORLAND
Simple lipids include fats, or triglycerides, and waxes. Fats are esters
of glycerol and higher fatty acids, and waxes are esters of higher fatty
alcohols and higher fatty acids. In this category may be included also
sterol esters and vitamin A esters. Compound lipids contain other groups
in addition to the alcohol, and in the subdivision of compound lipids
there are various schemes and terminologies. The present author feels
that the terms simple and compound do not serve any useful purpose
in the classification of lipids and prefers to follow subdivisions based
on the type of derivation as follows: (i) esters of glycerol (fats or
triglycerides); (ii) esters of long-chain fatty alcohols and sterols
(waxes); (iii) esters of glycerophosphoric acid coupled with a nitrogen
base and/or a carbohydrate (phospholipids), and (iv) derivatives of
the long-chain hydroxyamino alcohol sphingosine (sphingolipids).
1. Fats
These, as already indicated, are esters (II) of glycerol and higher
fatty acids
CH 2 · O · CO · Ri
CH · O · CO · R 2
I
CH 2 · O · CO · R 3
(Π)
where R 1? R 2 , and R 3 are fatty acid radicals.
Living tissues contain little or no free fatty acid, and the glycerides
present are triglycerides. However, monoglycerides occur in the hog
pancreas (58). The naturally occurring fats as isolated are not purely
triglycerides but contain unsaponifiable matter, including sterols, hydrocarbons, and alcohols. Related to the fats or triglycerides are the fatty
esters of the a-glyceryl ethers of n-octadec-9-enyl (selachyl), n-octadecyl
(batyl), and n-hexadecyl (chimyl) alcohols.
In natural fats the wide variety of fatty acids permits numerous
combinations within the glyceride molecule. According to the views of
Hilditch (3), no simple triglyceride is formed if any other combination
is possible. This is the rule of even distribution, which, according to
Hilditch, applies to most fats, although not with mathematical precision. To account for the relatively high content of fully saturated
glycerides in many stearic acid-rich animal fats, Hilditch suggested
that such fats are assembled on an even-distribution basis but are
later modified in the animal by hydrogenation (3).
Other workers have suggested that a random (59, 60) or a restrictedrandom (61) distribution operates. The evidence shows that the fatty
acids are widely distributed among the glyceride molecules, but it is