282
H A R R Y E A G L E A N D L E O N L E V I N T O W
metabolic scheme is not as clear, nor has it been shown to be essential
in human nutrition. Its requirement for the survival and growth of
cultured cells suggests that it indeed does play an essential role in a
fundamental metabolic process, at least in the minimal medium of
Table I.
Special circumstances are apparently involved in the requirement for
inositol, the metabolic function of which in animal nutrition is also
not clear. O f a number of cell lines tested, only one strain, the L-929
mouse fibroblast, was able to grow indefinitely in the absence of added
inositol, notwithstanding the fact that the capacity to synthesize
inositol from glucose appears to be a general property of cultured cells.
When the inositol-independent mouse cell-line was grown without
added inositol in a vessel separated by a semi-permeable membrane
from a similar culture of inositol-dependent cells, sufficient inositol
was released into the medium to permit the indefinite parabiotic
growth of the dependent line. This experiment provides an in vitro
model for the situation envisaged in most discussions of morphogenesis
and function, wherein one specialized tissue (or one cell type in a given
tissue) provides a nutrient essential for other tissues (or for other cells
in the same tissue). As in the case of choline, the degeneration and
death of cultured cells in the absence of inositol implies that, at least
under these conditions, this compound is necessary for a basic metabolic
reaction. The possibility that the requirement for inositol and choline,
like that for some of the amino acids, may be population-dependent,
is discussed in a following section (see also pp. 116, 247).
C M I S C E L L A N E O U S R E Q U I R E M E N T S
The mineral requirements of cultured cells in general parallel the
requirements of the mammalian organism as a whole. Calcium appears
to serve the special additional function of promoting the attachment
of cells grown as adherent monolayers, and suspended cultures can
multiply indefinitely in the absence of added calcium. This does not,
however, exclude an essential nutritional role for calcium, supplied as
a trace contaminant of other constituents of the medium. The same
considerations apply in the case of iron, which cultured cells presumably require for respiratory pigments, but for which no clear
nutritional requirement has been established. A need for trace metals
such as manganese, cobalt, zinc and copper is also possible, but has
not yet been demonstrated.
Under the usual conditions of growth in a minimal medium, cells
derive their energy largely through the utilization of carbohydrate,
with the glycolytic pathway usually predominating. The need for
relatively high concentrations of glucose, which can be met more or
H A R R Y E A G L E A N D L E O N L E V I N T O W
metabolic scheme is not as clear, nor has it been shown to be essential
in human nutrition. Its requirement for the survival and growth of
cultured cells suggests that it indeed does play an essential role in a
fundamental metabolic process, at least in the minimal medium of
Table I.
Special circumstances are apparently involved in the requirement for
inositol, the metabolic function of which in animal nutrition is also
not clear. O f a number of cell lines tested, only one strain, the L-929
mouse fibroblast, was able to grow indefinitely in the absence of added
inositol, notwithstanding the fact that the capacity to synthesize
inositol from glucose appears to be a general property of cultured cells.
When the inositol-independent mouse cell-line was grown without
added inositol in a vessel separated by a semi-permeable membrane
from a similar culture of inositol-dependent cells, sufficient inositol
was released into the medium to permit the indefinite parabiotic
growth of the dependent line. This experiment provides an in vitro
model for the situation envisaged in most discussions of morphogenesis
and function, wherein one specialized tissue (or one cell type in a given
tissue) provides a nutrient essential for other tissues (or for other cells
in the same tissue). As in the case of choline, the degeneration and
death of cultured cells in the absence of inositol implies that, at least
under these conditions, this compound is necessary for a basic metabolic
reaction. The possibility that the requirement for inositol and choline,
like that for some of the amino acids, may be population-dependent,
is discussed in a following section (see also pp. 116, 247).
C M I S C E L L A N E O U S R E Q U I R E M E N T S
The mineral requirements of cultured cells in general parallel the
requirements of the mammalian organism as a whole. Calcium appears
to serve the special additional function of promoting the attachment
of cells grown as adherent monolayers, and suspended cultures can
multiply indefinitely in the absence of added calcium. This does not,
however, exclude an essential nutritional role for calcium, supplied as
a trace contaminant of other constituents of the medium. The same
considerations apply in the case of iron, which cultured cells presumably require for respiratory pigments, but for which no clear
nutritional requirement has been established. A need for trace metals
such as manganese, cobalt, zinc and copper is also possible, but has
not yet been demonstrated.
Under the usual conditions of growth in a minimal medium, cells
derive their energy largely through the utilization of carbohydrate,
with the glycolytic pathway usually predominating. The need for
relatively high concentrations of glucose, which can be met more or