232
JOHN C. DITTMER
that perhaps the field of comparative biochemistry of phospholipids may
provide important information concerning the possible function of the
phospholipids.
It is with this in mind that certain privileges have been exercised in
the selection of material for inclusion here. There is an abundance of
literature relating to the occurrence of phospholipids in various animals,
plants, and microorganisms. Often nothing more is reported than the
per cent weight or molar concentration of phospholipids or lipid phosphorus. Because of the importance of stressing the individuality of the
different phospholipids as metabolic entities, in general, data of this
type have not been included. Emphasis has been laid as far as possible
on studies which distinguish to some degree the various types of phospholipids.
The fractionation of complex mixtures of phospholipids is difficult,
and it has been only in comparatively recent times that even a start
has been made toward the characterization of all the phospholipids of a
given tissue. It is not surprising then that some methods of analysis in
the past have been based on erroneous concepts and simplifications.
Older data presented here have been interpreted in the light of present
knowledge, and limitations have been pointed out when thought necessary. No attempt to give a historical presentation has been made, and
emphasis has been placed on the most recent data available. It is hoped
that any ambiguity which might arise from the nomenclature used, past
and present, has been eliminated by the definition of terms included
below in the discussion of structure.
II. Structure of the Glycerophosphatides
Regardless of source, those phospholipids which have been characterized are similar in structure and may be classified into two major
groups, the glycerophosphatides and sphingophosphatides. The glycerophosphatides are the more common; and as their name implies, all contain glycerophosphoric acid as a basic unit of structure. Further, from
the evidence available it is apparent that only L-a-glycerophosphoric acid
is present. In other words the phosphate moiety is esterified to the
primary hydroxyl group of glycerol; and as related to the corresponding
3-phosphoglyceraldehyde, the glycerophosphoric acid has the L-configuration. Reports in the older literature of ß-phosphoglycerides and
analyses given of mixtures of «- and /?-glycerophosphatides are generally based on the presence of a- and ^-glycerophosphoric acid in
hydrolyzates of phospholipids. It is now known that /^-glycerophosphoric
acid is formed during hydrolysis by migration of the phosphate radical
from the «-position. In no case has the natural occurrence of a ß-
JOHN C. DITTMER
that perhaps the field of comparative biochemistry of phospholipids may
provide important information concerning the possible function of the
phospholipids.
It is with this in mind that certain privileges have been exercised in
the selection of material for inclusion here. There is an abundance of
literature relating to the occurrence of phospholipids in various animals,
plants, and microorganisms. Often nothing more is reported than the
per cent weight or molar concentration of phospholipids or lipid phosphorus. Because of the importance of stressing the individuality of the
different phospholipids as metabolic entities, in general, data of this
type have not been included. Emphasis has been laid as far as possible
on studies which distinguish to some degree the various types of phospholipids.
The fractionation of complex mixtures of phospholipids is difficult,
and it has been only in comparatively recent times that even a start
has been made toward the characterization of all the phospholipids of a
given tissue. It is not surprising then that some methods of analysis in
the past have been based on erroneous concepts and simplifications.
Older data presented here have been interpreted in the light of present
knowledge, and limitations have been pointed out when thought necessary. No attempt to give a historical presentation has been made, and
emphasis has been placed on the most recent data available. It is hoped
that any ambiguity which might arise from the nomenclature used, past
and present, has been eliminated by the definition of terms included
below in the discussion of structure.
II. Structure of the Glycerophosphatides
Regardless of source, those phospholipids which have been characterized are similar in structure and may be classified into two major
groups, the glycerophosphatides and sphingophosphatides. The glycerophosphatides are the more common; and as their name implies, all contain glycerophosphoric acid as a basic unit of structure. Further, from
the evidence available it is apparent that only L-a-glycerophosphoric acid
is present. In other words the phosphate moiety is esterified to the
primary hydroxyl group of glycerol; and as related to the corresponding
3-phosphoglyceraldehyde, the glycerophosphoric acid has the L-configuration. Reports in the older literature of ß-phosphoglycerides and
analyses given of mixtures of «- and /?-glycerophosphatides are generally based on the presence of a- and ^-glycerophosphoric acid in
hydrolyzates of phospholipids. It is now known that /^-glycerophosphoric
acid is formed during hydrolysis by migration of the phosphate radical
from the «-position. In no case has the natural occurrence of a ß-