A Lecithin Lysolecithin and fatty
acids.
B Lysolecithin Glycero-phospho-choline
and fatty acids.
C Lecithin Phosphatidic acid and
choline.
D Lecithin Phosphoryl choline and
diglyceride.
Several fatty acids can be present in lecithin from various sources:
palmitic and oleic acid, besides the stearic acid which at first had
been thought the only one involved. In another group of extracts from
brain or nerve tissue, amino-ethanol H_{2}NCH_{2}CH_{2}OH is found
instead of the choline of lecithin. The variations include the alcohol,
to which the fatty acids and choline phosphate are attached, for
example, glycerol can be replaced by the so-called meat-sugar, inositol,
which has six hydroxyl groups in its hexagon-shaped molecule
C_{6}H_{6}(OH)_{6}.
[Illustration: Figure 14.--EDUARD BUCHNER (1860-1917) received the Nobel
Prize in Chemistry for his discovery of cell-free fermentation, the
first step in finding the role of phosphate in fermentations (1907).]
The generally similar behavior of these phosphate-and fat-containing
substances was emphasized by Ludwig Thudichum (1829-1901). He coined the
name phosphatides for this group of substances from seeds and
nerves.[29] His work on the phosphates in brain substance aroused
particular interest. When William Crookes drew his highly imaginative
picture of an "evolution" of the chemical elements, he put into it
"phosphorus for the brain, salt for the sea, clay for the solid
earth...."[30] But phosphatides occur in many places of organisms, in
bacteria, in leaves and roots of plants, in fat and tissues of animals.
And where phosphatides are found, there are also enzymes that
specifically act on them. They are called phosphatases to imply that
they split the phosphatides. In addition, enzymes are present, which
transfer phosphate groups from one compound to another. They are more
abundant in seeds of high fat content than in the more starch-containing
seeds, but even potatoes and orange juice have phosphatases.[31]
Thus, from phosphatides, phosphoric acid is generated, and they could
also be called phosphagens. Since 1926, however, the name phosphagens
has been reserved for a group of organic substances that release their
phosphoric acid very readily. The link between phosphorus and carbon is
provided by oxygen in the phosphatides, by nitrogen in the phosphagens.
In vertebrates, the basis for the phosphoric acid is creatine, whereas
invertebrates have arginine instead.
H OH OH
| / /
N--P=O NH--P=O
/ \ / \
C=NH OH C=NH OH
\ \
N--CH_{2}COOH NH
| |
CH_{3} CH_{2}
|
Creatine phosphate CH_{2}
|
CH_{2}
|
CHNH_{2}
|
COOH