156
WERNER BERGMANN
of certain red algae (32). Biosynthetic precursors of cholesterol have
also been isolated from plants, such as zymosterol (V, R = B), one of
the minor yeast sterols, and quite recently also a methylsterol, lophenol
(XII), from a cactus (57). The cholesterol skeleton of the twenty-seven
carbon atoms of cholesterol is also present in many of the sapogenins
and alkaloids found in higher plants.
Nevertheless the vast bulk of plant sterols as presently defined
carry substituents at C-24 of the side chain. Primitive plants such as
fungi, lichens, and certain algae produce preferentially the C-24 methyl
or methylene derivatives of cholesterol. Among the higher plants the
C-24 ethyl or ethylidene derivatives are the most conspicuous (18, 195).
The occurrence in plants of methylsterols substituted at C-24, such as
citrostadienol (4a-methyl-24-ethylidene-A
7 -cholestenol) (58), shows that
the side chain alkylation may well occur at one or the other of the stages
preceding the final step in the cholesterol biosynthesis.
While the vast majority of animal and plant sterols are of the Δ
5 -
type (II), A
7 -sterols (III) strikingly predominate in animals belonging to one of the order of sponges, to the most primitive class of mollusks, and to two of the classes of echinoderms. Such sterols are met
with also in plants, but their occurrence appears to be more sporadic
and less intimately associated with taxonomic features than in animals.
An outstanding exception are plants of the family of Cucurbitaceae in
which A
7 -sterols have always been found in major amounts (18). The
full significance of the preferential use of A
7 -sterols over A
5 -sterols still
remains to be elucidated, as is the striking predominance of saturated
sterols in certain sponges. The solutions to these and other problems,
which will lift the comparative biochemistry of sterols from the cataloguing stage to a level of true phylogenetic significance, are to come
not only from a broader and more detailed study of animal sterols, but
also from a better understanding of the biosynthesis and metabolism
of the sterols.
References
J. M. E. Chevreul, Ann. chim. et phys. 2, 339-372 (1816).
2. M. Berthelot, Ann. chim. et phys. (3) 56, 51-98 (1859).
3. W. M. Sperry, /. Biol. Chem. 114, 125-133 (1936).
4. M. Henze, Z. physioi. Chem. Hoppe Seylers 41, 109-124 (1904); 55, 427432 (1908).
5. T. Menozzi and A. Moreschi, Atti accad. nazl. Lincei, Rend. Classe sei. fis.
mat. e nut. (5) 19, 126-129 (1910).
6. C. Doree, Biochem. }. 4, 72-106 (1909).
7. A. Welsch, Ph.D. Dissertation, 58 pp., University of Freiburg, Germany,
1909.
8. W. Bergmann, /. Marine Research (Sears Foundation) 8, 137-176 (1949).
WERNER BERGMANN
of certain red algae (32). Biosynthetic precursors of cholesterol have
also been isolated from plants, such as zymosterol (V, R = B), one of
the minor yeast sterols, and quite recently also a methylsterol, lophenol
(XII), from a cactus (57). The cholesterol skeleton of the twenty-seven
carbon atoms of cholesterol is also present in many of the sapogenins
and alkaloids found in higher plants.
Nevertheless the vast bulk of plant sterols as presently defined
carry substituents at C-24 of the side chain. Primitive plants such as
fungi, lichens, and certain algae produce preferentially the C-24 methyl
or methylene derivatives of cholesterol. Among the higher plants the
C-24 ethyl or ethylidene derivatives are the most conspicuous (18, 195).
The occurrence in plants of methylsterols substituted at C-24, such as
citrostadienol (4a-methyl-24-ethylidene-A
7 -cholestenol) (58), shows that
the side chain alkylation may well occur at one or the other of the stages
preceding the final step in the cholesterol biosynthesis.
While the vast majority of animal and plant sterols are of the Δ
5 -
type (II), A
7 -sterols (III) strikingly predominate in animals belonging to one of the order of sponges, to the most primitive class of mollusks, and to two of the classes of echinoderms. Such sterols are met
with also in plants, but their occurrence appears to be more sporadic
and less intimately associated with taxonomic features than in animals.
An outstanding exception are plants of the family of Cucurbitaceae in
which A
7 -sterols have always been found in major amounts (18). The
full significance of the preferential use of A
7 -sterols over A
5 -sterols still
remains to be elucidated, as is the striking predominance of saturated
sterols in certain sponges. The solutions to these and other problems,
which will lift the comparative biochemistry of sterols from the cataloguing stage to a level of true phylogenetic significance, are to come
not only from a broader and more detailed study of animal sterols, but
also from a better understanding of the biosynthesis and metabolism
of the sterols.
References
J. M. E. Chevreul, Ann. chim. et phys. 2, 339-372 (1816).
2. M. Berthelot, Ann. chim. et phys. (3) 56, 51-98 (1859).
3. W. M. Sperry, /. Biol. Chem. 114, 125-133 (1936).
4. M. Henze, Z. physioi. Chem. Hoppe Seylers 41, 109-124 (1904); 55, 427432 (1908).
5. T. Menozzi and A. Moreschi, Atti accad. nazl. Lincei, Rend. Classe sei. fis.
mat. e nut. (5) 19, 126-129 (1910).
6. C. Doree, Biochem. }. 4, 72-106 (1909).
7. A. Welsch, Ph.D. Dissertation, 58 pp., University of Freiburg, Germany,
1909.
8. W. Bergmann, /. Marine Research (Sears Foundation) 8, 137-176 (1949).