302
J. A . L U C Y
diet, were required in culture under certain conditions. Thus tissues
not containing adequate glutamine synthetase required glutamine;
cystine was not needed by the embryonic chick tibia, and this observation was supported by an experiment in which rudiments apparently
synthesized cystine. Arginine, histidine and tyrosine are required in
culture, although they are not essential amino acids for man. This
situation is similar to that which has been found in experiments with
cell strains; to avoid undue repetition the reader is referred to Chapter
8, on serially propagated cells, for a discussion on this point.
I I I .
U T I L I Z A T I O N OF A M I N O A C I D S
A. I N T R O D U C T I O N
Despite the fact that the nutritional requirements of different tissues
in vitro are closely similar, it is to be expected that the utilization of
amino acids will vary from one tissue to another since the compounds
are being used for different purposes, especially in tissues that are
actively differentiating. The study of amino-acid utilization in culture
may therefore be used to obtain information on specific metabolic
processes that cannot be studied satisfactorily in the intact animal.
Explant and organ cultures have advantages over cell lines in such
investigations since cells cultured by the latter procedure possess a capacity to divide but frequently not the ability to fulfill the specific functions of their tissue of origin.
In order to compare patterns of amino-acid utilization between
different tissues, or the behaviour of the same tissue cultured under
different conditions, it is necessary to determine the removal of amino
acids from the medium on a quantitative basis. The studies reported in
the literature vary in the degree of accuracy to which amino-acid
utilization was measured, and in some the determinations were only
semi-quantitative. The accuracy required, however, is related to the
magnitude of the changes studied and these may be sufficiently great
in certain instances, for strictly quantitative measurements to be unnecessary. Careful attention should also be paid to the culture medium
used. If the defined medium is supplemented by "natural" materials
containing protein, the possibility that degradation of the protein
may occur during the experiment must be considered. Protein breakdown may yield amino acids additional to those initially provided in
the medium, and thereby vitiate measurements of changes in the
amino-acid content of the medium.
J. A . L U C Y
diet, were required in culture under certain conditions. Thus tissues
not containing adequate glutamine synthetase required glutamine;
cystine was not needed by the embryonic chick tibia, and this observation was supported by an experiment in which rudiments apparently
synthesized cystine. Arginine, histidine and tyrosine are required in
culture, although they are not essential amino acids for man. This
situation is similar to that which has been found in experiments with
cell strains; to avoid undue repetition the reader is referred to Chapter
8, on serially propagated cells, for a discussion on this point.
I I I .
U T I L I Z A T I O N OF A M I N O A C I D S
A. I N T R O D U C T I O N
Despite the fact that the nutritional requirements of different tissues
in vitro are closely similar, it is to be expected that the utilization of
amino acids will vary from one tissue to another since the compounds
are being used for different purposes, especially in tissues that are
actively differentiating. The study of amino-acid utilization in culture
may therefore be used to obtain information on specific metabolic
processes that cannot be studied satisfactorily in the intact animal.
Explant and organ cultures have advantages over cell lines in such
investigations since cells cultured by the latter procedure possess a capacity to divide but frequently not the ability to fulfill the specific functions of their tissue of origin.
In order to compare patterns of amino-acid utilization between
different tissues, or the behaviour of the same tissue cultured under
different conditions, it is necessary to determine the removal of amino
acids from the medium on a quantitative basis. The studies reported in
the literature vary in the degree of accuracy to which amino-acid
utilization was measured, and in some the determinations were only
semi-quantitative. The accuracy required, however, is related to the
magnitude of the changes studied and these may be sufficiently great
in certain instances, for strictly quantitative measurements to be unnecessary. Careful attention should also be paid to the culture medium
used. If the defined medium is supplemented by "natural" materials
containing protein, the possibility that degradation of the protein
may occur during the experiment must be considered. Protein breakdown may yield amino acids additional to those initially provided in
the medium, and thereby vitiate measurements of changes in the
amino-acid content of the medium.