264
J O H N P A U L
et al> unpublished) and lactic dehydrogenase, aldolase and cytochrome
oxidase, found to be influenced by growth at low oxygen tension by
Adebonojo et al. (1961). These observations suggest a situation similar
in some ways to that found in yeast where the enzyme lactic dehydrogenase fluctuates according to whether the cells are grown aerobically
or anaerobically (Slonimski, 1953). Their interest lies in the fact that
they may provide an explanation for the persistently low respiration
displayed by cells which have been exposed to low oxygen tension for
several days (Paul, 1961).
Much of our knowledge of the behaviour of inducible enzymes is
derived from studies of /?-galactosidase in bacteria. Maio and Rickenberg (1960) have identified this enzyme in animal tissues and also in cell
strains. However, although they showed that the enzyme is present in
much higher amounts in the intestinal mucosa of young animals
(which utilize lactose) they were unable to induce it in cultures of the
strain-L cell.
Another glucosidase, ^-glucuronidase, has been observed by ourselves to vary considerably at different times in cultures of several cell
strains (Paul and Freshney, 1965) and it seems not unlikely that it is
inducible.
In the whole animal it has been claimed that by altering the amount
and nature of carbohydrate available, alterations in the amounts of
many enzymes of carbohydrate metabolism can be obtained (Fitch and
Chaikoff, 1960). This has not been verified with cultured cells. However, if the existence of adaptive enzymes turns out to be widespread, it
may reveal the capacity for cells to adapt to different patterns of
carbohydrate metabolism by these means.
4. The Influence of Hormones
It has always seemed attractive to use cultured cells for the study of
hormonal activity but it should be stated at the outset that the results of
most of this research have been disappointing. This may be because
specific target cells are not usually cultured and it may be for this reason
that organ cultures have yielded more encouraging results. Insulin,
corticosteroids and thyroid hormones have all been studied for their
influence on carbohydrate metabolism and some effects have been
obtained although usually with rather larger amounts than could be
considered physiological.
(a) Insulin. The most positive results have been obtained with insulin
and three effects have been reported: increased glycolysis; increased
growth; and increased pinocytosis.
Increased glycolysis on the addition of insulin to the culture medium
has been reported for several cell strains by different workers (Etingof
J O H N P A U L
et al> unpublished) and lactic dehydrogenase, aldolase and cytochrome
oxidase, found to be influenced by growth at low oxygen tension by
Adebonojo et al. (1961). These observations suggest a situation similar
in some ways to that found in yeast where the enzyme lactic dehydrogenase fluctuates according to whether the cells are grown aerobically
or anaerobically (Slonimski, 1953). Their interest lies in the fact that
they may provide an explanation for the persistently low respiration
displayed by cells which have been exposed to low oxygen tension for
several days (Paul, 1961).
Much of our knowledge of the behaviour of inducible enzymes is
derived from studies of /?-galactosidase in bacteria. Maio and Rickenberg (1960) have identified this enzyme in animal tissues and also in cell
strains. However, although they showed that the enzyme is present in
much higher amounts in the intestinal mucosa of young animals
(which utilize lactose) they were unable to induce it in cultures of the
strain-L cell.
Another glucosidase, ^-glucuronidase, has been observed by ourselves to vary considerably at different times in cultures of several cell
strains (Paul and Freshney, 1965) and it seems not unlikely that it is
inducible.
In the whole animal it has been claimed that by altering the amount
and nature of carbohydrate available, alterations in the amounts of
many enzymes of carbohydrate metabolism can be obtained (Fitch and
Chaikoff, 1960). This has not been verified with cultured cells. However, if the existence of adaptive enzymes turns out to be widespread, it
may reveal the capacity for cells to adapt to different patterns of
carbohydrate metabolism by these means.
4. The Influence of Hormones
It has always seemed attractive to use cultured cells for the study of
hormonal activity but it should be stated at the outset that the results of
most of this research have been disappointing. This may be because
specific target cells are not usually cultured and it may be for this reason
that organ cultures have yielded more encouraging results. Insulin,
corticosteroids and thyroid hormones have all been studied for their
influence on carbohydrate metabolism and some effects have been
obtained although usually with rather larger amounts than could be
considered physiological.
(a) Insulin. The most positive results have been obtained with insulin
and three effects have been reported: increased glycolysis; increased
growth; and increased pinocytosis.
Increased glycolysis on the addition of insulin to the culture medium
has been reported for several cell strains by different workers (Etingof