252
GEORGE G. LATIES
that certain metabolic intermediates arising only during aerobic metabolism are required for growth. The experiments to be described indicate that the energetic contribution of the aerobic respiratory process is
in fact indispensable to growth.
A. The Terminal Oxidase Related to Growth
In tissues such as the potato tuber, in which more than one terminal
oxidase may participate in the total respiratory oxygen consumption, it
would be of great interest to know whether certain physiological activities of the cell are exclusively associated with the functioning of any
particular terminal oxidase. Whether or not more than one oxidative
system is present, it is important to characterize the active terminal oxidase and to relate its activity to particular physiological processes such
as growth.
Some insight into the nature of the terminal oxidase of intact tissue
may be obtained from the relation of the respiration rate to the partial
pressure of oxygen, as well as from the action of inhibitors known to
combine with the heavy metal prosthetic groups of oxidases. James
(1953c), who has discussed the validity of deductions which may be
drawn from inhibitor experiments, has pointed out that experiments
dealing with the reversibility by light of CO-inhibited respiratory systems
may distinguish between the copper-containing and iron-containing
terminal oxidases. Thus, whereas polyphenolase, a copper enzyme, is
inhibited by CO, the inhibition is not relieved by light. In contrast,
the inhibition of cytochrome oxidase, an iron-containing terminal oxidase, is completely reversible by light under proper conditions. Ascorbic
oxidase (a copper enzyme) is sometimes inhibited by CO (see James,
1953c), but in any event the inhibition is not reversible by light. Cyanide, which effectively inhibits all three of the oxidases named, both in
the light and in the dark, is clearly an unsuitable inhibitor with which
to distinguish them.
Cytochrome oxidase may also be distinguished from the copper oxidases on the basis of its affinity for oxygen. Whereas cytochrome oxidase
is completely oxygen-saturated at a fraction of 1% of an atmosphere of
oxygen (Winzler, 1941), ascorbic oxidase in air functions at but half
the maximal rate, and at a mere 10% of the maximal rate in 2.5% oxygen
(Thimann et al, 1954). Polyphenolase activity is approximately 60%
that in air in 5% oxygen (Ingraham, 1955).
Since the affinity of cytochrome oxidase for oxygen is approximately
ten times that for CO, and since these gases combine with the oxidase in
a competitive fashion, it has been necessary in the past to lower the
oxygen concentration to 5% in order to obtain a ratio of CO to 0 2 (19
GEORGE G. LATIES
that certain metabolic intermediates arising only during aerobic metabolism are required for growth. The experiments to be described indicate that the energetic contribution of the aerobic respiratory process is
in fact indispensable to growth.
A. The Terminal Oxidase Related to Growth
In tissues such as the potato tuber, in which more than one terminal
oxidase may participate in the total respiratory oxygen consumption, it
would be of great interest to know whether certain physiological activities of the cell are exclusively associated with the functioning of any
particular terminal oxidase. Whether or not more than one oxidative
system is present, it is important to characterize the active terminal oxidase and to relate its activity to particular physiological processes such
as growth.
Some insight into the nature of the terminal oxidase of intact tissue
may be obtained from the relation of the respiration rate to the partial
pressure of oxygen, as well as from the action of inhibitors known to
combine with the heavy metal prosthetic groups of oxidases. James
(1953c), who has discussed the validity of deductions which may be
drawn from inhibitor experiments, has pointed out that experiments
dealing with the reversibility by light of CO-inhibited respiratory systems
may distinguish between the copper-containing and iron-containing
terminal oxidases. Thus, whereas polyphenolase, a copper enzyme, is
inhibited by CO, the inhibition is not relieved by light. In contrast,
the inhibition of cytochrome oxidase, an iron-containing terminal oxidase, is completely reversible by light under proper conditions. Ascorbic
oxidase (a copper enzyme) is sometimes inhibited by CO (see James,
1953c), but in any event the inhibition is not reversible by light. Cyanide, which effectively inhibits all three of the oxidases named, both in
the light and in the dark, is clearly an unsuitable inhibitor with which
to distinguish them.
Cytochrome oxidase may also be distinguished from the copper oxidases on the basis of its affinity for oxygen. Whereas cytochrome oxidase
is completely oxygen-saturated at a fraction of 1% of an atmosphere of
oxygen (Winzler, 1941), ascorbic oxidase in air functions at but half
the maximal rate, and at a mere 10% of the maximal rate in 2.5% oxygen
(Thimann et al, 1954). Polyphenolase activity is approximately 60%
that in air in 5% oxygen (Ingraham, 1955).
Since the affinity of cytochrome oxidase for oxygen is approximately
ten times that for CO, and since these gases combine with the oxidase in
a competitive fashion, it has been necessary in the past to lower the
oxygen concentration to 5% in order to obtain a ratio of CO to 0 2 (19