2. STEROLS: STRUCTURE AND DISTRIBUTION
153
squirts (Ascidians) of the subphylum Tunicata have been the subject
of exploratory studies. Cholesterol has been found to be the primary
sterol of Styela plicata (96), Phallusia mammilata (190), and Microcosmus sulcatus (195). It is accompanied by other sterols such as
clionasterol and poriferasterol. The Japanese species, Cynthia roretzi
(154), has afforded a sterol mixture containing a A
5 '
7 -sterol, tentatively
identified as 7-dehydrostigmasterol (I, R = K). Poriferasterol and clionasterol were identified among the remaining sterols, but the presence
of cholesterol was not ascertained. Preliminary as they are, these observations point to the possibility that species of Tunicata may differ
significantly in their sterol content, and that such differences may reveal
interesting phylogenetic relationships.
The sterols of vertebrates have been the subject of numerous investigations. In all species has cholesterol been found to be the principal
sterol. It is generally accompanied by small amounts of cholestanol
(I, R = A), 7-dehydrocholesterol (I, R = A), and A
7 -cholestenol (III,
R = A). In skin sterols, and in particular in those from rats, A
7 -cholestenol may be present in quantities equal to if not exceeding those of
cholesterol (11). Large quantities of trimethylsterols, such as lanosterol
(IX), are found in certain hair fats, such as wool grease (lanolin).
A A
5 -sterol quite different from cholesterol and not of the order of
C 27 has been isolated from the poisonous skin secretions of the toad
Bufo vulgaris and other species. In its properties (m.p. 146°, [a] D
—38°; acetate, m.p. 137°; dihydroderivative, m.p. 140°; acetate, m.p.
138°, [a] D +119, it closely resembles γ-sitosterol (II, R = L) (191).
The same sterol, accompanied by from five to twenty times the amount
of cholesterol, has also been isolated from toad skins. This interesting
observation emphasizes the rather peculiar character of the biochemistry
of this primitive vertebrate in which the synthesis of "digitalis-like"
heart poisons and the excretion of arginine are prominent features.
XI. Conclusions
The survey of the distribution and structures of animal sterols which
was begun fifty years ago remains far from completion. The catalogue
of information does not yet include representatives of several phyla,
among which the Brachiopoda, the Bryozoa, and the Phoronides are of
particular phylogenetic interest. Species of other phyla are represented
in numbers still too inadequate to permit drawing conclusions of more
than transitory value. The survey has concerned itself almost exclusively with the sterols as they are obtained from animals, rather
than their origin. With the exception of some protozoans and insects,
very little is known about the origin of sterols in invertebrates. As yet
153
squirts (Ascidians) of the subphylum Tunicata have been the subject
of exploratory studies. Cholesterol has been found to be the primary
sterol of Styela plicata (96), Phallusia mammilata (190), and Microcosmus sulcatus (195). It is accompanied by other sterols such as
clionasterol and poriferasterol. The Japanese species, Cynthia roretzi
(154), has afforded a sterol mixture containing a A
5 '
7 -sterol, tentatively
identified as 7-dehydrostigmasterol (I, R = K). Poriferasterol and clionasterol were identified among the remaining sterols, but the presence
of cholesterol was not ascertained. Preliminary as they are, these observations point to the possibility that species of Tunicata may differ
significantly in their sterol content, and that such differences may reveal
interesting phylogenetic relationships.
The sterols of vertebrates have been the subject of numerous investigations. In all species has cholesterol been found to be the principal
sterol. It is generally accompanied by small amounts of cholestanol
(I, R = A), 7-dehydrocholesterol (I, R = A), and A
7 -cholestenol (III,
R = A). In skin sterols, and in particular in those from rats, A
7 -cholestenol may be present in quantities equal to if not exceeding those of
cholesterol (11). Large quantities of trimethylsterols, such as lanosterol
(IX), are found in certain hair fats, such as wool grease (lanolin).
A A
5 -sterol quite different from cholesterol and not of the order of
C 27 has been isolated from the poisonous skin secretions of the toad
Bufo vulgaris and other species. In its properties (m.p. 146°, [a] D
—38°; acetate, m.p. 137°; dihydroderivative, m.p. 140°; acetate, m.p.
138°, [a] D +119, it closely resembles γ-sitosterol (II, R = L) (191).
The same sterol, accompanied by from five to twenty times the amount
of cholesterol, has also been isolated from toad skins. This interesting
observation emphasizes the rather peculiar character of the biochemistry
of this primitive vertebrate in which the synthesis of "digitalis-like"
heart poisons and the excretion of arginine are prominent features.
XI. Conclusions
The survey of the distribution and structures of animal sterols which
was begun fifty years ago remains far from completion. The catalogue
of information does not yet include representatives of several phyla,
among which the Brachiopoda, the Bryozoa, and the Phoronides are of
particular phylogenetic interest. Species of other phyla are represented
in numbers still too inadequate to permit drawing conclusions of more
than transitory value. The survey has concerned itself almost exclusively with the sterols as they are obtained from animals, rather
than their origin. With the exception of some protozoans and insects,
very little is known about the origin of sterols in invertebrates. As yet