9. P R O T E I N M E T A B O L I S M IN C U L T U R E
305
I V . P R O T E I N M E T A B O L I S M
A. SYNTHESIS
The synthesis of proteins can be studied at many different levels,
e.g. in the whole animal, tissue slices, cultured tissue and in cell-free
homogenates. Tissue culture is particularly valuable for the study of
the synthesis of specialized proteins, such as collagen and keratin,
that are produced by differentiating cells, in view of the technical
difficulties involved in any investigations of the synthesis of these proteins by means of such sub-cellular systems as have been successfully
employed, for example, in the study of haemoglobin synthesis.
The biosynthesis of collagen in vitro has been studied by Jackson and
Smith (1957) who used suspension^ v of osteoblasts obtained directly
from frontal bones of fowl embryos and then grown in a fluid, fibrinfree medium. Appreciable quantities of protein-bound hydroxyproline
were formed during the first 24 h of growth, but no typical collagen
fibrils were observed with the electron-microscope. Since the subsequent
formation of characteristic collagen fibrils was not associated with a
significant rise in the mean hydroxyproline content of the tissue, it
was suggested that collagen-forming cells synthesize a hydroxyprolinerich precursor which subsequently becomes transformed directly into
collagen fibrils It was also observed that high concentrations of unlabeled hydroxyproline in the medium did not affect the synthesis of
hydroxyproline from labelled proline, indicating that proline was
utilized in preference to hydroxyproline in the formation of collagen,
(Smith and Jackson, 1957). Chvapil, Holeckova, Cmuchalova, Kobrle
and Hurych (1962), in studies on fibroblasts from the lungs of 11-day
chick embryos, have observed that silicic acid stimulates the production of collagen.
In an autoradiographic study, Pelc and Fell (1960) investigated the
incorporation of radioactive cystine, methionine, leucine and tyrosine
during the inhibition of keratinization and transformation of the
epidermis into a mucous epithelium, that occur in embryonic chick
skin grown in vitro in the presence of excess of vitamin A. All four of
these amino acids were incorporated into the epidermal nuclei as well
as into the cytoplasm. Vitamin A had no significant effect on the
showed a striking increase of arginase activity in tissue grown on control
medium as compared with that in freshly isolated prostate glands; in
cultures grown in the presence of methylcholanthrene the increase in
arginase activity was much less than in the controls.
305
I V . P R O T E I N M E T A B O L I S M
A. SYNTHESIS
The synthesis of proteins can be studied at many different levels,
e.g. in the whole animal, tissue slices, cultured tissue and in cell-free
homogenates. Tissue culture is particularly valuable for the study of
the synthesis of specialized proteins, such as collagen and keratin,
that are produced by differentiating cells, in view of the technical
difficulties involved in any investigations of the synthesis of these proteins by means of such sub-cellular systems as have been successfully
employed, for example, in the study of haemoglobin synthesis.
The biosynthesis of collagen in vitro has been studied by Jackson and
Smith (1957) who used suspension^ v of osteoblasts obtained directly
from frontal bones of fowl embryos and then grown in a fluid, fibrinfree medium. Appreciable quantities of protein-bound hydroxyproline
were formed during the first 24 h of growth, but no typical collagen
fibrils were observed with the electron-microscope. Since the subsequent
formation of characteristic collagen fibrils was not associated with a
significant rise in the mean hydroxyproline content of the tissue, it
was suggested that collagen-forming cells synthesize a hydroxyprolinerich precursor which subsequently becomes transformed directly into
collagen fibrils It was also observed that high concentrations of unlabeled hydroxyproline in the medium did not affect the synthesis of
hydroxyproline from labelled proline, indicating that proline was
utilized in preference to hydroxyproline in the formation of collagen,
(Smith and Jackson, 1957). Chvapil, Holeckova, Cmuchalova, Kobrle
and Hurych (1962), in studies on fibroblasts from the lungs of 11-day
chick embryos, have observed that silicic acid stimulates the production of collagen.
In an autoradiographic study, Pelc and Fell (1960) investigated the
incorporation of radioactive cystine, methionine, leucine and tyrosine
during the inhibition of keratinization and transformation of the
epidermis into a mucous epithelium, that occur in embryonic chick
skin grown in vitro in the presence of excess of vitamin A. All four of
these amino acids were incorporated into the epidermal nuclei as well
as into the cytoplasm. Vitamin A had no significant effect on the
showed a striking increase of arginase activity in tissue grown on control
medium as compared with that in freshly isolated prostate glands; in
cultures grown in the presence of methylcholanthrene the increase in
arginase activity was much less than in the controls.