Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:1.9.3.1 (cytochrome oxidase)
 8,822 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The relationship between oxygen concentrations in arteries, cytosol, and mitochondria and high energy phosphate metabolism was studied in perfused rat hearts subjected to low and high workloads during gradual hypoxia. PCr, ATP, and Pi were measured by 31P-NMR. Myoglobin oxygenation and cytochrome aa3 oxidation were measured by the optical method. When influent oxygen tension was decreased gradually, PCr, ATP, %MbO2, %Cytaa3, cardiac work and MvO2 decreased while Pi and Pi/PCr increased in Langendorff and working hearts. These changes occurred, however, at higher PaO2 values in working hearts. The decrease of %MbO2 and %Cytaa3 in Langendorff hearts was parallel where the ratio of %MbO2 / %Cytaa3 was 1:1. However, this ratio was more than 1:1 in working hearts. It had been demonstrated that oxygen gradients change with changing oxygen consumption. Metabolic and heart work changes occurred simultaneously and significant changes occurred at low levels of %MbO2 and %Cytaa3. Some differences were observed between Langendorff and working hearts. Oxidative phosphorylation is a good indicator of ATP synthesis during hypoxia and is regulated by the intracellular oxygen concentration as well as oxygen gradients.
 ...
PMID:Oxygen dependence of energy state and cardiac work in the perfused rat heart. 196 60

Myoglobin-mediated oxygen delivery to intracellular mitochondria is demonstrated in cardiac myocytes isolated from the hearts of mature rats. Myocytes are held at high ambient oxygen pressure, 40-340 torr (5-45 kPa); sarcoplasmic myoglobin is fully oxygenated. In this condition oxygen availability does not limit respiratory rate; myoglobin-facilitated diffusion contributes no additional oxygen flux and, since oxygen consumption is measured in steady states, the storage function of myoglobin vanishes. Carbon monoxide, introduced stepwise, displaces oxygen from intracellular oxymyoglobin without altering the optical spectrum of the largely oxidized intracellular mitochondria. A large part, about one-third, of the steady-state oxygen uptake is abolished by carbon monoxide blockade of myoglobin oxygenation. The myoglobin-dependent component of the oxygen uptake decreases linearly with decreasing fraction of intracellular oxymyoglobin, with a slope near unity. Studies using inhibitors of mitochondrial electron transport indicate that myoglobin-delivered oxygen uptake depends on electron flow through the mitochondrial electron transport chain. We conclude that cardiac mitochondria accept two additive simultaneous flows of oxygen: a flow of dissolved oxygen to cytochrome oxidase and a flow of myoglobin-bound oxygen to a mitochondrial terminus. Myoglobin-mediated oxygen delivery supports ATP generation by heart cells at physiological ambient oxygen pressure.
 ...
PMID:Myoglobin-mediated oxygen delivery to mitochondria of isolated cardiac myocytes. 311 70

Myoglobin, the monomeric haemoprotein expressed in red muscle, is reported in biochemistry and physiology textbooks to function as an intracellular oxygen carrier and oxygen reservoir. Here, Maurizio Brunori argues that myoglobin can also play the role of intracellular scavenger of nitric oxide, an inhibitor of mitochondrial cytochrome-c oxidase, thereby protecting respiration in the skeletal muscle and the heart.
 ...
PMID:Nitric oxide, cytochrome-c oxidase and myoglobin. 1116 12

The heart and those striated muscles that contract for long periods, having available almost limitless oxygen, operate in sustained steady states of low sarcoplasmic oxygen pressure that resist change in response to changing muscle work or oxygen supply. Most of the oxygen pressure drop from the erythrocyte to the mitochondrion occurs across the capillary wall. Within the sarcoplasm, myoglobin, a mobile carrier of oxygen, is developed in response to mitochondrial demand and augments the flow of oxygen to the mitochondria. Myoglobin-facilitated oxygen diffusion, perhaps by virtue of reduction of dimensionality of diffusion from three dimensions towards two dimensions in the narrow spaces available between mitochondria, is rapid relative to other parameters of cell respiration. Consequently, intracellular gradients of oxygen pressure are shallow, and sarcoplasmic oxygen pressure is nearly the same everywhere. Sarcoplasmic oxygen pressure, buffered near 0.33 kPa (2.5 torr; equivalent to approximately 4 micro mol l(-1) oxygen) by equilibrium with myoglobin, falls close to the operational K(m) of cytochrome oxidase for oxygen, and any small increment in sarcoplasmic oxygen pressure will be countered by increased oxygen utilization. The concentration of nitric oxide within the myocyte results from a balance of endogenous synthesis and removal by oxymyoglobin-catalyzed dioxygenation to the innocuous nitrate. Oxymyoglobin, by controlling sarcoplasmic nitric oxide concentration, helps assure the steady state in which inflow of oxygen into the myocyte equals the rate of oxygen consumption.
 ...
PMID:Myoglobin function reassessed. 1275 83