AJP - Cell Physiology, Vol 258, Issue 3 C504-C511, Copyright © 1990 by American Physiological Society
The polyphasic nature of the respiratory process at the mitochondrial level
B. D. Reynafarje and P. W. Davies
Department of Biological Chemistry, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
The kinetics of oxygen consumption by rat liver mitochondria, respiring
under a variety of metabolic conditions, have been studied. Respiration was
initiated by injecting oxygen into anaerobic suspensions of mitochondria.
It was found that, irrespective of the metabolic state of the mitochondria
and the nature of the respiratory substrate, the rates of electron flow and
oxygen consumption follow the pattern of a polyphasic reaction. The rates
of oxygen uptake during the first phase are extremely fast and depend on
oxygen concentration. The second phase represents a transition in which net
oxidation of cytochrome-c oxidase stops and the rates of oxygen consumption
suddenly decrease. The third phase is characterized by its changeability.
Depending on initial conditions the rates may increase, decrease, or remain
constant, although the reaction is not one of zero order. During the last
phase, the rates decrease and the oxidase becomes increasingly reduced. It
is postulated that the mitochondrial respiratory process is basically a
cyclic event in which the redox state of the membrane and the rates of
oxygen consumption oscillate with amplitudes and frequencies conditioned by
the energy demand and energy-yielding capacity of the cell.
