[Illustration: Figure 20.--FRITZ A. LIPMANN (b. 1899) shared with Hans
Adolf Krebs the Nobel Prize in Medicine and Physiology in 1953 for his
work on coenzyme A. He discovered acetyl phosphate as the substance in
bacteria, which transfers phosphate to adenylic acid.]
[Illustration: Figure 21.--ALEXANDER R. TODD (b. 1907) received the
Nobel Prize in Chemistry in 1957 for his research on nucleotides. He
determined the position of the phosphate groups in the molecule and
confirmed it by synthesis of dinucleotide phosphates.]
Its function is connected with the transfer of hydrogen between
intermediates formed through phosphate-transferring enzymes.
Fermentation proceeds by a cascade of processes, in which phosphate
groups swing back and forth, and equilibria between ATP with ADP play a
major role.
Many of the enzymes are closely related to vitamins. Thus, cocarboxylase
A, which takes part in the separation of carbon dioxide from an
intermediate fermentation product, is the phosphate of vitamin B_{1}.
Others of the B vitamins contain phosphate groups, for example those of
the B_{2} and B_{6} group, and in B_{12}, one lonely phosphate forms a
bridge in the large molecule that contains one atom of cobalt:
C_{63}H_{90}N_{14}O_{14}PCo. The formation of vitamin A from carotine
occurs under the influence of ATP.
The first stages in fermentation are like those in respiration, which
ends with carbon dioxide and water. These two are the materials for the
reverse process in photosynthesis. When light is absorbed by the
chlorophyll of green plants, one of the initial reactions is a transfer
of hydrogen from water to a triphosphopyridine nucleotide, which later
acts to reduce the carbon dioxide. Under the influence of ATP,
phosphoglyceric acid is synthesized and further built up by way of
carbohydrate phosphates to hexose sugars and finally to starch. In many
starchy fruits, a small proportion of phosphate remains attached to the
end product.
The synthesis of proteins is under the control of deoxyribonucleic acid
or ribonucleic acid, abbreviated by the symbols DNA and RNA. The genes
in the nucleus are parts of a giant DNA molecule. RNA is a universal
constituent of all living cells. Where protein synthesis is intense, the
content in RNA is high. Thus, the spinning glands of silkworms are
extraordinarily rich in RNA.[37]
In his research on the radioactive isotope P^32, George de Hevesy gained
some insight into the surprising mobility of phosphates in organisms: "A
phosphate radical taken up with the food may first participate in the
phosphorylation of glucose in the intestinal mucose, soon afterwards
pass into the circulation as free phosphate, enter a red corpuscle,
become incorporated with an adenosine triphosphoric-acid molecule,
participate in a glycolytic process going on in the corpuscle, return to
circulation, penetrate into the liver cells, participate in the
formation of a phosphatide molecule, after a short interval enter the
circulation in this form, penetrate into the spleen, and leave this
organ after some time as a constituent of a lymphocyte. We may meet the
phosphate radical again as a constituent of the plasma, from which it
may find its way into the skeleton."[38] Much has been added in the last
30 years to complete this picture in many details and to extend it to
other biochemical processes, including even the changes of the pigments
in the retina in the visual process, or in the conversion of chemical
energy to light by bacteria and insects.