112
C H A R I T Y W A Y M O U T H
but the stimulating effects of iron are now recognized for several cell
systems (Neuman and Tytell, 1961). Positive effects of other ions in
particular instances have been demonstrated, and could in any case
be predicted with a high degree of probability, from their role as
activators in important enzyme systems common to many cells. Detailed
studies of the optimum concentrations of trace elements require, not
merely knowing the effects of supplements added to the synthetic
media, but also analysis of the ions present adventitiously as true
"traces" in the supposedly defined medium. Trowell (1952) reported
that one batch of reagent grade (AR) NaCl contained enough K (i.e.
2-85°/o) to provide the amount specified in the Tyrode formula. This
example directs attention to the desirability of knowing the true
composition, rather than that deduced from the label on the bottle.
In this particular case, however, it is very questionable whether Tyrode
himself, in 1910, had access to salts of higher purity than had Trowell
in 1952, for compounding his empirical formulation. For this reason,
Tyrode's solution made up with highly purified salts in the quantities
specified by the author might differ from the mixture that Tyrode
actually found effective.
The carbohydrate most widely used in media is the natural hexose,
glucose, though this can be replaced by other sugars in several cases
(Harris and Kutsky, 1953; Eagle, Barban, Levy and Schulze, 1958a;
Morgan and Morton, 1960), and nutritional variants capable of using
other sugars, or lactate, as sole carbohydrate or intermediate, have
been isolated (Chang, 1957). Glucose takes part in many biosyntheses.*
In addition to the predominant pathway of oxidation to lactic acid,
glucose enters into the formation of many molecular species, e.g.
amino acids, ribose, deoxyribose, glucosamine and galactosamine.
While the early media usually contained amounts of glucose close to
those for human (about 100 mg°/o) or bird (about 200 mg°/o) blood,
most of the later formulae contain higher concentrations, well above
those that would be considered "physiological".
The amino acids have been the subject of many studies, which will
not be reviewed in full detail here, since their metabolism forms the
subject matter of Chapter 9 and other good and very complete summaries
of work on amino-acid utilization in Tissue Culture have been published
recently by Lucy (1960), Greenstein and Winitz (1961) and Levintow
and Eagle (1961). Amino acids are key compounds in cell metabolism
and indispensable for growing cells. The question whether, and if so
to what extent, cells utilize whole proteins has never been clearly
settled, though the evidence suggests, as might be expected, that the
ability to do so correlates with the presence of effective proteolytic
*For further discussion of carbohydrate metabolism in cultures see Chapter 8.
C H A R I T Y W A Y M O U T H
but the stimulating effects of iron are now recognized for several cell
systems (Neuman and Tytell, 1961). Positive effects of other ions in
particular instances have been demonstrated, and could in any case
be predicted with a high degree of probability, from their role as
activators in important enzyme systems common to many cells. Detailed
studies of the optimum concentrations of trace elements require, not
merely knowing the effects of supplements added to the synthetic
media, but also analysis of the ions present adventitiously as true
"traces" in the supposedly defined medium. Trowell (1952) reported
that one batch of reagent grade (AR) NaCl contained enough K (i.e.
2-85°/o) to provide the amount specified in the Tyrode formula. This
example directs attention to the desirability of knowing the true
composition, rather than that deduced from the label on the bottle.
In this particular case, however, it is very questionable whether Tyrode
himself, in 1910, had access to salts of higher purity than had Trowell
in 1952, for compounding his empirical formulation. For this reason,
Tyrode's solution made up with highly purified salts in the quantities
specified by the author might differ from the mixture that Tyrode
actually found effective.
The carbohydrate most widely used in media is the natural hexose,
glucose, though this can be replaced by other sugars in several cases
(Harris and Kutsky, 1953; Eagle, Barban, Levy and Schulze, 1958a;
Morgan and Morton, 1960), and nutritional variants capable of using
other sugars, or lactate, as sole carbohydrate or intermediate, have
been isolated (Chang, 1957). Glucose takes part in many biosyntheses.*
In addition to the predominant pathway of oxidation to lactic acid,
glucose enters into the formation of many molecular species, e.g.
amino acids, ribose, deoxyribose, glucosamine and galactosamine.
While the early media usually contained amounts of glucose close to
those for human (about 100 mg°/o) or bird (about 200 mg°/o) blood,
most of the later formulae contain higher concentrations, well above
those that would be considered "physiological".
The amino acids have been the subject of many studies, which will
not be reviewed in full detail here, since their metabolism forms the
subject matter of Chapter 9 and other good and very complete summaries
of work on amino-acid utilization in Tissue Culture have been published
recently by Lucy (1960), Greenstein and Winitz (1961) and Levintow
and Eagle (1961). Amino acids are key compounds in cell metabolism
and indispensable for growing cells. The question whether, and if so
to what extent, cells utilize whole proteins has never been clearly
settled, though the evidence suggests, as might be expected, that the
ability to do so correlates with the presence of effective proteolytic
*For further discussion of carbohydrate metabolism in cultures see Chapter 8.