7. C A R B O H Y D R A T E A N D E N E R G Y M E T A B O L I S M
247
avian tissue) but the criteria employed were also different. Harris and
Kutsky (1953) measured the radius o f t h e outgrowth from explants;
Morgan and Morton (1960) measured the survival of primary explants
in a depleted medium; Eagle and his colleagues (1958) measured the
amount of growth (as cell protein synthesized) in a given time, while
Wachtl and Kinsey based their conclusions on mitotic counts (1957).
Consequently, only limited significance can be attached to the minor
differences observed in these studies. A few of the discrepancies can be
accounted for quite easily. For instance, Harris and Kutsky (1953)
noted that both glycogen and maltose were hydrolysed to glucose by
extracellular enzymes in the embryo extract used in their experiments.
In the same way the utilization of sugar phosphates may depend on the
presence of phosphatases in the medium or at the cell surface since most
phosphates cannot enter cells readily (Morton and Morgan, 1960).
One or two variant cell lines are of some interest. Chang and Liepins
(1957) obtained variants of HeLa and conjunctival cells which utilize
xylose preferentially as an energy source. Other workers have made
similar observations (Bradley and Syverton, 1960; Hsu and Kellogg,
1959) and these illuminate the possibilities of using nutritional variants
in genetic and biochemical studies. O f even greater interest, perhaps,
in this respect is the observation made by Krooth and Weinberg (1960)
that whereas cells obtained by skin biopsy from normal people can
utilize galactose, strains derived in the same way from individuals with
hereditary galactosaemia are unable to do so. These cells lack the
enzyme galactose-1-phosphate uridyl transferase. The same authors
also found that galactose in the medium is inhibitory to growth of
galactosaemic cells when glucose is available in very low concentration.
Agol (1960a, b , c) also observed that in cultures of monkey kidney
cortex galactose competitively inhibits glycolysis although it has no
effect in cell homogenates. On the basis of this observation Agol
suggests that galactose competes for a carrier, which cannot be hexokinase since this enzyme is not inhibited by galactose.
One special carbohydrate requirement, that for myo-inositol, is of
particular interest. While this substance can be synthesized by the
tissues of both mammals and birds, deficiency symptoms have sometimes been reported when it is not supplied in the diet. Eagle and his
colleagues (1957) found that myo-inositol was essential for the growth
of nineteen cell strains in continuous culture. However, some lines
which do not require inositol have also been described and at least one
example has been reported of the use of a myo-inositol-synthesizing line
as a feeder culture for cells which are themselves dependent on an
extraneous supply (Eagle, Agranoff and Snell, 1960). Newly explanted
and "transformed" lines may differ in their requirement (Chang, 1961).
247
avian tissue) but the criteria employed were also different. Harris and
Kutsky (1953) measured the radius o f t h e outgrowth from explants;
Morgan and Morton (1960) measured the survival of primary explants
in a depleted medium; Eagle and his colleagues (1958) measured the
amount of growth (as cell protein synthesized) in a given time, while
Wachtl and Kinsey based their conclusions on mitotic counts (1957).
Consequently, only limited significance can be attached to the minor
differences observed in these studies. A few of the discrepancies can be
accounted for quite easily. For instance, Harris and Kutsky (1953)
noted that both glycogen and maltose were hydrolysed to glucose by
extracellular enzymes in the embryo extract used in their experiments.
In the same way the utilization of sugar phosphates may depend on the
presence of phosphatases in the medium or at the cell surface since most
phosphates cannot enter cells readily (Morton and Morgan, 1960).
One or two variant cell lines are of some interest. Chang and Liepins
(1957) obtained variants of HeLa and conjunctival cells which utilize
xylose preferentially as an energy source. Other workers have made
similar observations (Bradley and Syverton, 1960; Hsu and Kellogg,
1959) and these illuminate the possibilities of using nutritional variants
in genetic and biochemical studies. O f even greater interest, perhaps,
in this respect is the observation made by Krooth and Weinberg (1960)
that whereas cells obtained by skin biopsy from normal people can
utilize galactose, strains derived in the same way from individuals with
hereditary galactosaemia are unable to do so. These cells lack the
enzyme galactose-1-phosphate uridyl transferase. The same authors
also found that galactose in the medium is inhibitory to growth of
galactosaemic cells when glucose is available in very low concentration.
Agol (1960a, b , c) also observed that in cultures of monkey kidney
cortex galactose competitively inhibits glycolysis although it has no
effect in cell homogenates. On the basis of this observation Agol
suggests that galactose competes for a carrier, which cannot be hexokinase since this enzyme is not inhibited by galactose.
One special carbohydrate requirement, that for myo-inositol, is of
particular interest. While this substance can be synthesized by the
tissues of both mammals and birds, deficiency symptoms have sometimes been reported when it is not supplied in the diet. Eagle and his
colleagues (1957) found that myo-inositol was essential for the growth
of nineteen cell strains in continuous culture. However, some lines
which do not require inositol have also been described and at least one
example has been reported of the use of a myo-inositol-synthesizing line
as a feeder culture for cells which are themselves dependent on an
extraneous supply (Eagle, Agranoff and Snell, 1960). Newly explanted
and "transformed" lines may differ in their requirement (Chang, 1961).