300
J. A . L U C Y
alanine, proline, aspartic acid and glutamic acid were synthesized from
glucose and incorporated into protein by organ cultures of embryonic
chick cartilage It is of interest that these workers also found that the
amino acids, glycine and aspartic acid were themselves the precursors
of adenine, guanine, cytosine, uracil and thymine which were subsequently incorporated into nucleic acids For comparative purposes,
data on the chemical composition of long-bone rudiments of the
embryonic chick were obtained, including the amino-acid contents of
the acid-insoluble (non-collagenous) proteins of the tissue (Biggers,
Lawson, Lucy and Webb, 1961). Kieny (1958), Wolff (1957) and
Stenger-Haffen (1957) have reported studies on fowl tibia, syrinx and
gonads respectively in which certain amino-acid requirements were
determined; in these studies the medium was supplemented with agar
which may have contained unrecognized sources of nutrients.
c. " E S S E N T I A L " A M I N O ACIDS
Threonine, valine, leucine, tyrosine, phenylalanine,
arginine,
histidine, lysine and tryptophan were found by Morgan and Morton
(1957) to be essential amino acids for nutritionally depleted explants of
chick embryonic heart-tissue cultivated in a chemically defined medium.
Isoleucine, as mentioned above, was non-essential under these conditions. This unexpected finding may have been the result of traces of
isoleucine remaining in the tissue stores at the end of the depletion
treatment. Large quantities of tyrosine have been shown to be toxic
for chick heart-tissue in the absence of phenylalanine; addition of
increasing quantities of tyrosine to the medium prolonged survival
time only in the presence of phenylalanine (Morton and Morgan,
1959). Seventeen structurally related compounds were tested for their
ability to substitute for phenylalanine or tyrosine in the nutrition of
fragments from embryonic chick heart. DL-Alanyl-DL-phenylalanine
replaced phenylalanine; all other compounds had negligible effects and
most were toxic at high concentrations (Morton and Morgan, 1961).
It was found by Morgan, Morton and Pasieka (1958) that a high
concentration of citrulline, but not ornithine, may be used in place of
arginine for explants of chick heart-tissue. From this and other observations, it was concluded that only part of the arginine cycle was
functioning in this tissue.
The sulphur-containing amino acids, cystine and methionine, have
both been shown to be essential for nutritionally depleted explants of
embryonic chick heart (Morgan and Morton, 1957). Cystine can be
replaced to a limited degree by ergothionine, oxidized glutathione or
lanthionine (Morton and Morgan, 1958). The inclusion of methionine
J. A . L U C Y
alanine, proline, aspartic acid and glutamic acid were synthesized from
glucose and incorporated into protein by organ cultures of embryonic
chick cartilage It is of interest that these workers also found that the
amino acids, glycine and aspartic acid were themselves the precursors
of adenine, guanine, cytosine, uracil and thymine which were subsequently incorporated into nucleic acids For comparative purposes,
data on the chemical composition of long-bone rudiments of the
embryonic chick were obtained, including the amino-acid contents of
the acid-insoluble (non-collagenous) proteins of the tissue (Biggers,
Lawson, Lucy and Webb, 1961). Kieny (1958), Wolff (1957) and
Stenger-Haffen (1957) have reported studies on fowl tibia, syrinx and
gonads respectively in which certain amino-acid requirements were
determined; in these studies the medium was supplemented with agar
which may have contained unrecognized sources of nutrients.
c. " E S S E N T I A L " A M I N O ACIDS
Threonine, valine, leucine, tyrosine, phenylalanine,
arginine,
histidine, lysine and tryptophan were found by Morgan and Morton
(1957) to be essential amino acids for nutritionally depleted explants of
chick embryonic heart-tissue cultivated in a chemically defined medium.
Isoleucine, as mentioned above, was non-essential under these conditions. This unexpected finding may have been the result of traces of
isoleucine remaining in the tissue stores at the end of the depletion
treatment. Large quantities of tyrosine have been shown to be toxic
for chick heart-tissue in the absence of phenylalanine; addition of
increasing quantities of tyrosine to the medium prolonged survival
time only in the presence of phenylalanine (Morton and Morgan,
1959). Seventeen structurally related compounds were tested for their
ability to substitute for phenylalanine or tyrosine in the nutrition of
fragments from embryonic chick heart. DL-Alanyl-DL-phenylalanine
replaced phenylalanine; all other compounds had negligible effects and
most were toxic at high concentrations (Morton and Morgan, 1961).
It was found by Morgan, Morton and Pasieka (1958) that a high
concentration of citrulline, but not ornithine, may be used in place of
arginine for explants of chick heart-tissue. From this and other observations, it was concluded that only part of the arginine cycle was
functioning in this tissue.
The sulphur-containing amino acids, cystine and methionine, have
both been shown to be essential for nutritionally depleted explants of
embryonic chick heart (Morgan and Morton, 1957). Cystine can be
replaced to a limited degree by ergothionine, oxidized glutathione or
lanthionine (Morton and Morgan, 1958). The inclusion of methionine