466
0. B. COWEY AND J. R. SARGENT
systems within the cell. The importance and essentiality of phospholipids seem to lie in this structural role. Mitochondria for instance
contain large amounts of lipid and over 90% of this is phospholipid ; it
is present as an integral part of the membrane system and submitochondria1 particles, when separated, retain their phospholipid
components.
Choline deficiency in chinook salmon led to very low growth rates
(Halver, 1957) and to haemorrhages in both kidney and intestine.
Halver suggests that methyl group donation from methionine may have
spared the choline requirement of the fish. This pathway of choline
synthesis probably proceeds by way of phosphatidyl precursors and
intermediates. Methyl groups from " active " methionine (S-adenosyl
methionine) are transferred to phosphatidyl serine with the eventual
formation of phosphatidyl choline.
The choline requirement of fish is probably dependent on the
availability and activity of methyl donating systems ; for chinook
salmon 60-60 mg/kg body weightlday of choline is necessary.
10. Vitamin B,,
Vitamin B,, (cyanocobalamin) is one of the most recently isolated
and characterized of the vitamins. It is a complex molecule containing
cobalt, with a minimum molecular weight of about 1 300, and is composed of a highly substituted reduced corrin ring, somewhat like porphyrin ring systems, and a nucleotide portion in which the nitrogen
base is 5-, 6-dimethyl benzimidazole. Many analogues of vitamin B,,
have been isolated; these commonly have either the cyanide radical
replaced by another radical (hydroxyl) or contain a different nitrogen
base in the nucleotide.
In man vitamin B,, deficiency leads to pernicious anaemia but
no megaloblastic anaemias occur in deficient animal. In young animals
vitamin B,, deficiency leads to severely retarded growth with high
mortality. Vitamin B,, is now in fact recognized as being the so-called
" animal protein factor " associated previously with many natural
products of animal origin.
Although coenzyme forms of vitamin B,, (cobamides) have been
isolated in recent years the far reaching effects of vitamin B,, deficiency
in animal growth cannot yet be explained in terms of a specific
metabolic function of vitamin B12.
These cobamides are concerned (i) in certain mutase reactions which
catalyse the migration of a group from one part of a molecule to a
different part of the same molecule, as in the conversion of methyl
0. B. COWEY AND J. R. SARGENT
systems within the cell. The importance and essentiality of phospholipids seem to lie in this structural role. Mitochondria for instance
contain large amounts of lipid and over 90% of this is phospholipid ; it
is present as an integral part of the membrane system and submitochondria1 particles, when separated, retain their phospholipid
components.
Choline deficiency in chinook salmon led to very low growth rates
(Halver, 1957) and to haemorrhages in both kidney and intestine.
Halver suggests that methyl group donation from methionine may have
spared the choline requirement of the fish. This pathway of choline
synthesis probably proceeds by way of phosphatidyl precursors and
intermediates. Methyl groups from " active " methionine (S-adenosyl
methionine) are transferred to phosphatidyl serine with the eventual
formation of phosphatidyl choline.
The choline requirement of fish is probably dependent on the
availability and activity of methyl donating systems ; for chinook
salmon 60-60 mg/kg body weightlday of choline is necessary.
10. Vitamin B,,
Vitamin B,, (cyanocobalamin) is one of the most recently isolated
and characterized of the vitamins. It is a complex molecule containing
cobalt, with a minimum molecular weight of about 1 300, and is composed of a highly substituted reduced corrin ring, somewhat like porphyrin ring systems, and a nucleotide portion in which the nitrogen
base is 5-, 6-dimethyl benzimidazole. Many analogues of vitamin B,,
have been isolated; these commonly have either the cyanide radical
replaced by another radical (hydroxyl) or contain a different nitrogen
base in the nucleotide.
In man vitamin B,, deficiency leads to pernicious anaemia but
no megaloblastic anaemias occur in deficient animal. In young animals
vitamin B,, deficiency leads to severely retarded growth with high
mortality. Vitamin B,, is now in fact recognized as being the so-called
" animal protein factor " associated previously with many natural
products of animal origin.
Although coenzyme forms of vitamin B,, (cobamides) have been
isolated in recent years the far reaching effects of vitamin B,, deficiency
in animal growth cannot yet be explained in terms of a specific
metabolic function of vitamin B12.
These cobamides are concerned (i) in certain mutase reactions which
catalyse the migration of a group from one part of a molecule to a
different part of the same molecule, as in the conversion of methyl