216
GEORGE G. LATIES
the past been studied exhaustively, and thus offer the opportunity to
correlate related physiological phenomena.
I. THE REGULATION OF RESPIRATORY RATE
Respiratory rate will be regarded most simply as the quantity of
oxygen consumed in unit time by a unit quantity of tissue. Classically,
the regulation of respiratory rate in plant tissues has been considered in
terms of the external and internal factors which control respiration. External factors will not be discussed below, with the exception of the interrelation of respiration and oxygen tension under certain conditions.
James (1953a) has recently dealt extensively with this aspect of rate
control. An enormous number of internal factors may, of course, affect
the rate of respiration, but it would be inaccurate to consider that all
among that great variety of internal factors regulate the respiration rate.
Regulation, in a more rigorous sense, connotes a process whereby either
homeostasis is achieved, or respiration is geared to the metabolic requirements of the cell. In either case a type of feedback mechanism is
implied, wherein respiration affects the metabolic events in the cell, and
these events in turn affect the respiration. Thus, although the variety and
concentration of enzymes, substrates, and inorganic salts, the pH, and
the type and prevalence of hormones and growth substances are factors
which affect the rate of respiration, they do not ordinarily regulate the
rate of respiration in the sense described.
Hunter (1951) has reviewed the sequence of observations which has
led us to recognize that during respiration inorganic phosphate is incorporated into organic forms of such a nature that the subsequent
removal of phosphate is attended by a large loss in free energy. Lipmann (1941) introduced the convention of regarding the energy contained within such organic phosphate compounds as inhering in the
phosphate bond itself, and termed the link a high-energy bond, and the
phosphate molecule, high-energy phosphate. In contradistinction to the
high-energy phosphate bond, the simple esterified form of phosphate,
such as is found in glucose-6-phosphate, is considered a low-energy bond.
During the last few years a series of elegant investigations (see Hunter,
1951; Green, 1954) has more explicitly elucidated the relationship between the oxidation of certain metabolic intermediates and the concomitant incorporation of inorganic phosphate into high-energy compounds. As a corollary, the manner in which oxidative phosphorylation
may control the respiration rate in a way which meets the requirements
of true regulation has been envisaged.
It has been demonstrated that, depending on the substrate, from two
to four high-energy phosphate bonds are produced for each pair of
GEORGE G. LATIES
the past been studied exhaustively, and thus offer the opportunity to
correlate related physiological phenomena.
I. THE REGULATION OF RESPIRATORY RATE
Respiratory rate will be regarded most simply as the quantity of
oxygen consumed in unit time by a unit quantity of tissue. Classically,
the regulation of respiratory rate in plant tissues has been considered in
terms of the external and internal factors which control respiration. External factors will not be discussed below, with the exception of the interrelation of respiration and oxygen tension under certain conditions.
James (1953a) has recently dealt extensively with this aspect of rate
control. An enormous number of internal factors may, of course, affect
the rate of respiration, but it would be inaccurate to consider that all
among that great variety of internal factors regulate the respiration rate.
Regulation, in a more rigorous sense, connotes a process whereby either
homeostasis is achieved, or respiration is geared to the metabolic requirements of the cell. In either case a type of feedback mechanism is
implied, wherein respiration affects the metabolic events in the cell, and
these events in turn affect the respiration. Thus, although the variety and
concentration of enzymes, substrates, and inorganic salts, the pH, and
the type and prevalence of hormones and growth substances are factors
which affect the rate of respiration, they do not ordinarily regulate the
rate of respiration in the sense described.
Hunter (1951) has reviewed the sequence of observations which has
led us to recognize that during respiration inorganic phosphate is incorporated into organic forms of such a nature that the subsequent
removal of phosphate is attended by a large loss in free energy. Lipmann (1941) introduced the convention of regarding the energy contained within such organic phosphate compounds as inhering in the
phosphate bond itself, and termed the link a high-energy bond, and the
phosphate molecule, high-energy phosphate. In contradistinction to the
high-energy phosphate bond, the simple esterified form of phosphate,
such as is found in glucose-6-phosphate, is considered a low-energy bond.
During the last few years a series of elegant investigations (see Hunter,
1951; Green, 1954) has more explicitly elucidated the relationship between the oxidation of certain metabolic intermediates and the concomitant incorporation of inorganic phosphate into high-energy compounds. As a corollary, the manner in which oxidative phosphorylation
may control the respiration rate in a way which meets the requirements
of true regulation has been envisaged.
It has been demonstrated that, depending on the substrate, from two
to four high-energy phosphate bonds are produced for each pair of