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J O H N P A U L
material took place or, if it did, it was within the limits imposed by the
size of intracellular pools at the time when oxygen was removed. This
seems quite a likely explanation. The pools in many animal cells are
quite large and will support a doubling of most cellular components
before synthesis diminishes; (b) the medium provided a full complement
of all those components which require oxidative pathways for their
synthesis. This possibility can certainly not be excluded because all
these reports refer to primary explants maintained in "natural" media—
mostly media containing large amounts of embryo extract which is a
rich source of amino acids and nucleic-acid derivatives. Furthermore,
autolysis within the explant could have contributed to the needs of the
explants; (c) the system contained a hydrogen acceptor other than
oxygen; (d) the criteria of growth were faulty. Few of these experiments
were carried out for very long and some of them relied on migration or
mitosis as criteria of growth. Both migration and mitosis can, of course,
occur without nett synthesis of cellular material, and both can apparently continue for a short time in anaerobic conditions.
3. Mitosis and Respiration
It has been known for some time that cell division may proceed
through one cycle in conditions of complete anaerobiosis and even in
the presence of high concentrations of inhibitors of the electron transport systems. Thus Pomerat and Willmer (1939) found that cells would
divide in a medium containing 0*002 M cyanide or saturated with
carbon monoxide. Swann's (1953) experiments on reversible inhibition
of the cytochromes in sea urchin eggs show that, up to a certain stage,
cell division is dependent on an intact electron transfer system, but
after that stage the entire process, including actual cleavage, can go on
in its absence. On this basis he postulated the accumulation of a pool of
energy-rich material which had to reach a given level before division
can take place. This work is open to other interpretations but it indicates
that certain parts of the mitotic process certainly do not require oxygen.
Whether aerobic pathways are essential for the remainder or whether
they are merely necessary for the synthesis of nucleic acids and proteins,
as already discussed, still awaits rigorous proof.
The purpose of this discussion has not been to answer the question
"Can cells grow in the absence of oxygen?" Rather has it been intended
to illuminate the meaninglessness of the question in the absence of more
precise definition of the conditions employed. It would seem possible
that in a medium with a complete supplement of amino acids, nucleosides, etc., cells might be able to obtain all their energy for division by
glycolysis. In these conditions cells with a greater than normal capacity
for glycolysis might, of course, be at an advantage.
J O H N P A U L
material took place or, if it did, it was within the limits imposed by the
size of intracellular pools at the time when oxygen was removed. This
seems quite a likely explanation. The pools in many animal cells are
quite large and will support a doubling of most cellular components
before synthesis diminishes; (b) the medium provided a full complement
of all those components which require oxidative pathways for their
synthesis. This possibility can certainly not be excluded because all
these reports refer to primary explants maintained in "natural" media—
mostly media containing large amounts of embryo extract which is a
rich source of amino acids and nucleic-acid derivatives. Furthermore,
autolysis within the explant could have contributed to the needs of the
explants; (c) the system contained a hydrogen acceptor other than
oxygen; (d) the criteria of growth were faulty. Few of these experiments
were carried out for very long and some of them relied on migration or
mitosis as criteria of growth. Both migration and mitosis can, of course,
occur without nett synthesis of cellular material, and both can apparently continue for a short time in anaerobic conditions.
3. Mitosis and Respiration
It has been known for some time that cell division may proceed
through one cycle in conditions of complete anaerobiosis and even in
the presence of high concentrations of inhibitors of the electron transport systems. Thus Pomerat and Willmer (1939) found that cells would
divide in a medium containing 0*002 M cyanide or saturated with
carbon monoxide. Swann's (1953) experiments on reversible inhibition
of the cytochromes in sea urchin eggs show that, up to a certain stage,
cell division is dependent on an intact electron transfer system, but
after that stage the entire process, including actual cleavage, can go on
in its absence. On this basis he postulated the accumulation of a pool of
energy-rich material which had to reach a given level before division
can take place. This work is open to other interpretations but it indicates
that certain parts of the mitotic process certainly do not require oxygen.
Whether aerobic pathways are essential for the remainder or whether
they are merely necessary for the synthesis of nucleic acids and proteins,
as already discussed, still awaits rigorous proof.
The purpose of this discussion has not been to answer the question
"Can cells grow in the absence of oxygen?" Rather has it been intended
to illuminate the meaninglessness of the question in the absence of more
precise definition of the conditions employed. It would seem possible
that in a medium with a complete supplement of amino acids, nucleosides, etc., cells might be able to obtain all their energy for division by
glycolysis. In these conditions cells with a greater than normal capacity
for glycolysis might, of course, be at an advantage.