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
301
in the medium, in the absence of cystine, had no beneficial effect upon
the survival time of the explants; combination of a high concentration
of L-cystine in the presence of D-methionine reduced the survival of
the cultures to that obtained in the complete absence of the sulphur
amino acids (Morgan and Morton, 1956).
Biggers et al. (1957) found threonine, valine, isoleucine, leucine,
tyrosine, phenylalanine, arginine, histidine, lysine and tryptophan to
be essential for the embryonic chick tibia cultured in a chemically
defined medium. More recently, Biggers, Gwatkin and Heyner (1961)
have demonstrated that a medium lacking these amino acids and also
methionine and cysteine cannot support growth of embryonic bones
from the rat, mouse and chick. A defined medium from which glutamine
was omitted was also inadequate. Glutamic acid does not affect the
response in length of embryonic chick tibia to glutamine and there was
no evidence that glutamic acid is a precursor of glutamine (Biggers,
1961). With regard to the sulphur-containing amino acids, it was
noted that, unlike explants of chick heart, neither cystine nor cysteine
was essential for chick limb-bone rudiments but methionine was
required (Biggers et al. } 1957). Webb and Biggers (1961) observed
that weak radioactivity was associated frequently, but not invariably,
with cystine obtained from the acid-insoluble protein of embryonic
bone-rudiments cultured in the presence of radioactive glucose. Kieny
(1958) found that methionine was essential for the tibia but that cysteine
was inhibitory. Cystine and methionine were indispensable for embryonic fowl gonads, (Stenger-Haffen, 1957), while cystine was described
as indispensable and methionine as essential for the embryonic fowl
syrinx in organ cultures (Wolff, 1957).
D . D I S C U S S I O N
The number of nutritional studies that have been reported on explant
and organ cultures is relatively few as compared with those in which
cell strains have been used. Nevertheless, the available data indicate a
distinct pattern of "non-essential" and "essential" amino acids,
although classification in this way is by no means rigid. The eight
amino acids that are essential to man; isoleucine, leucine, valine,
threonine, phenylalanine, lysine, tryptophan and methionine, have
all proved to be essential in explant and organ cultures of various
tissues with the exception, as discussed above, of isoleucine for explants
of chick heart-tissue. Other amino acids: alanine, glycine, serine,
proline, hydroxyproline, aspartic acid and glutamic acid, which are
not essential for man, are also non-essential for explant and organ
cultures. Glutamine and cystine, which are not essential in a normal
301
in the medium, in the absence of cystine, had no beneficial effect upon
the survival time of the explants; combination of a high concentration
of L-cystine in the presence of D-methionine reduced the survival of
the cultures to that obtained in the complete absence of the sulphur
amino acids (Morgan and Morton, 1956).
Biggers et al. (1957) found threonine, valine, isoleucine, leucine,
tyrosine, phenylalanine, arginine, histidine, lysine and tryptophan to
be essential for the embryonic chick tibia cultured in a chemically
defined medium. More recently, Biggers, Gwatkin and Heyner (1961)
have demonstrated that a medium lacking these amino acids and also
methionine and cysteine cannot support growth of embryonic bones
from the rat, mouse and chick. A defined medium from which glutamine
was omitted was also inadequate. Glutamic acid does not affect the
response in length of embryonic chick tibia to glutamine and there was
no evidence that glutamic acid is a precursor of glutamine (Biggers,
1961). With regard to the sulphur-containing amino acids, it was
noted that, unlike explants of chick heart, neither cystine nor cysteine
was essential for chick limb-bone rudiments but methionine was
required (Biggers et al. } 1957). Webb and Biggers (1961) observed
that weak radioactivity was associated frequently, but not invariably,
with cystine obtained from the acid-insoluble protein of embryonic
bone-rudiments cultured in the presence of radioactive glucose. Kieny
(1958) found that methionine was essential for the tibia but that cysteine
was inhibitory. Cystine and methionine were indispensable for embryonic fowl gonads, (Stenger-Haffen, 1957), while cystine was described
as indispensable and methionine as essential for the embryonic fowl
syrinx in organ cultures (Wolff, 1957).
D . D I S C U S S I O N
The number of nutritional studies that have been reported on explant
and organ cultures is relatively few as compared with those in which
cell strains have been used. Nevertheless, the available data indicate a
distinct pattern of "non-essential" and "essential" amino acids,
although classification in this way is by no means rigid. The eight
amino acids that are essential to man; isoleucine, leucine, valine,
threonine, phenylalanine, lysine, tryptophan and methionine, have
all proved to be essential in explant and organ cultures of various
tissues with the exception, as discussed above, of isoleucine for explants
of chick heart-tissue. Other amino acids: alanine, glycine, serine,
proline, hydroxyproline, aspartic acid and glutamic acid, which are
not essential for man, are also non-essential for explant and organ
cultures. Glutamine and cystine, which are not essential in a normal