A complete model of oxygen consumption by mitochondrial cytochrome c oxidase
Lead Research Organisation:
University of Essex
Department Name: Biological Sciences
Abstract
Our bodies derive most of their useable energy from the controlled burning (oxidation) of fats, proteins and carbohydrates by the gas, oxygen. Oxygen delivery to organs (heart, brain etc.) is therefore vital for health, growth and development. Problems with oxygen delivery or consumption are responsible for the bad effects of many disease processes e.g. brain damage after a stroke, heart attacks etc. Nearly all (>95%) of the oxygen in the body is consumed by a small organ (organelle) found inside all cells. This is called the mitochondrion. Inside the mitochondrion one protein catalyst (enzyme) called cytochrome c oxidase (CCO) consumes all the oxygen; the oxygen is converted into water, generating a voltage across the mitochondrion that eventually is used to make a molecule called adenosine triphosphate (ATP); ATP is the universal energy currency of all cells and drives muscle movement, brain signalling, growth, development, tissue repair etc. CCO contains a number of coloured iron and copper centres that, uniquely, make it possible to detect it in intact humans e.g. in the brain during 'thinking' or in the muscle during exercise. The purpose of this grant is to study how CCO is controlled in the body, in particular in order to improve our understanding of these signals that we can measure non-invasively. This is a complex problem that we will address by using a combination of in vitro (test tube) experiments and mathematical modelling. It utilises the expertises of biology, physics, mathematics, biochemistry and cell biology. We will first optimise the measurement of the different coloured signals in the test tube. We will then look at how these signals are controlled in vitro. From this our ultimate aim is to develop a dynamic mathematical model that will demonstrate how it might be controlled in the whole body (in vivo). We will focus in this project on one organ (the brain) for two reasons; the brain is critically dependent on oxygen for survival and there is a lot of in vivo data about its oxygen consumption and delivery to the brain. A key part of our understanding of this complex system is to understand how it works at a range of levels. We will therefore develop models of how oxygen is consumed in CCO on its own, CCO within the mitochondrion and CCO in the whole brain. We will use appropriate experiments at each level of organisation to define and test how the model works. In particular we will ask colleagues from around the world to analyse our model critically, both with respect to their data and their own theories. The ultimate aim will be to understand how this complex biological system works at both a 'reductionist' molecular and more 'holistic' organ level. As well as being of interest for its own sake, an improved description of this system is likely to have significance for healthcare and industry (in particular for people manufacturing machines that measure parameters relating to oxygen and energetics in the body.
Technical Summary
Mitochondrial oxygen consumption is the dominant energy transduction pathway in mammalian systems. The control of this system is complex and integrates with other pathways at both biochemical and physiological levels. There is lot of knowledge about the mitochondrial electron transfer system at the level of mechanistic enzymology, but the detailed regulation of electron flow within the enzymes is still a matter of live debate. The purpose of this grant is to model the regulation of this complex energy transduction pathway at multiple levels / the individual enzyme (cytochrome c oxidase, CCO), the organelle (mitochondrion) and the organ (brain). The collection of new in vitro steady state date will be integrated with model building with experiment and model feeding off each other. A particular interest will be how to make optimal use of the data generated via non-invasive monitoring of haemoglobin and CCO in the brain by near infrared (NIR) techniques. First we will optimise the deconvolution of the in vitro spectra of the relevant CCO chromophores that are detectable by visible and NIR spectroscopy. This is required for the measurements of intermediate concentrations in the in vitro and in vivo steady state. We will then perform a detailed study of the factors regulating CCO intermediates in the purified enzyme, artificial proteoliposomes, rat brain mitochondria and cells, enabling us to develop a complete steady state kinetic model of CCO . This will then be incorporated into a kinetic model of mitochondrial energy metabolism. Finally the revised mitochondrial model will be incorporated into an ongoing model of brain blood flow, autoregulation and metabolism. This will allow current in vivo measurements of CCO redox state to be accessible to this model, assisting with both the in vivo testing of the model and its relevance to accessible real time measurements in animal studies and human volunteers and patients.
People |
ORCID iD |
Christopher Cooper (Principal Investigator) |
Publications
Banaji M
(2008)
A model of brain circulation and metabolism: NIRS signal changes during physiological challenges.
in PLoS computational biology
Cooper C
(2009)
Oxygen Transport to Tissue XXX
Cooper CE
(2008)
The inhibition of mitochondrial cytochrome oxidase by the gases carbon monoxide, nitric oxide, hydrogen cyanide and hydrogen sulfide: chemical mechanism and physiological significance.
in Journal of bioenergetics and biomembranes
Cooper CE
(2009)
Steady state redox levels in cytochrome oxidase: relevance for in vivo near infrared spectroscopy (NIRS).
in Advances in experimental medicine and biology
Cooper CE
(2008)
A dynamic model of nitric oxide inhibition of mitochondrial cytochrome c oxidase.
in Biochimica et biophysica acta
Cooper CE
(2007)
Nitric oxide regulation of mitochondrial oxygen consumption II: Molecular mechanism and tissue physiology.
in American journal of physiology. Cell physiology
Mason MG
(2009)
Cytochrome bd confers nitric oxide resistance to Escherichia coli.
in Nature chemical biology
Mason MG
(2009)
The steady-state mechanism of cytochrome c oxidase: redox interactions between metal centres.
in The Biochemical journal
Mason MG
(2014)
Re-evaluation of the near infrared spectra of mitochondrial cytochrome c oxidase: Implications for non invasive in vivo monitoring of tissues.
in Biochimica et biophysica acta
Mason MG
(2008)
A quantitative approach to nitric oxide inhibition of terminal oxidases of the respiratory chain.
in Methods in enzymology
Description | Our bodies derive most of their useable energy from the controlled burning (oxidation) of fats, proteins and carbohydrates by the gas, oxygen. Oxygen delivery to organs (heart, brain etc.) is therefore vital for health, growth and development. Problems with oxygen delivery or consumption are responsible for the bad effects of many disease processes e.g. brain damage after a stroke, heart attacks etc. Nearly all (>95%) of the oxygen in the body is consumed by a small organ (organelle) found inside all cells. This is called the mitochondrion. Inside the mitochondrion one protein catalyst (enzyme) called cytochrome c oxidase (CCO) consumes all the oxygen; the oxygen is converted into water, generating a voltage across the mitochondrion that eventually is used to make a molecule called adenosine triphosphate (ATP); ATP is the universal energy currency of all cells and drives muscle movement, brain signalling, growth, development, tissue repair etc. CCO contains a number of coloured iron and copper centres that, uniquely, make it possible to detect it in intact humans e.g. in the brain during "thinking" or in the muscle during exercise. The purpose of this grant was to study how CCO is controlled in the body, in particular in order to improve our understanding of these signals that we can measure non- invasively. This is a complex problem that was addressed by using a combination of in vitro (test tube) experiments and mathematical modelling. It utilised the expertises of biology, physics, mathematics, biochemistry and cell biology. We first optimised the measurement of the different coloured signals in the test tube. We then looked at how these were controlled in vitro. We discovered that two species (called P and F and representing different forms of oxygen bound to CCO) were not detectable, contrary to the theories of other authors. However, we did discover changes in a coloured species absorbing red light (655 nm) that reported on the changes in a copper centre at the enzyme active site. These measurements changed the current ideas about the mechanism of oxygen consumption by CCO. Using this information we developed a dynamic mathematical model that demonstrated how oxygen consumption is controlled in the whole body (in vivo). We focused in this project on one organ (the brain) for two reasons; the brain is critically dependent on oxygen for survival and there is a lot of in vivo data about its oxygen consumption and delivery to the brain. We developed models of how oxygen is consumed in CCO on its own and CCO in the whole brain. These models helped us to understand the interplay between blood flow and oxygen consumption occurring when the brain is active (functional activation). As well as being of interest for its own sake, our improved description of this system is likely to have significance for healthcare and industry (in particular for people manufacturing machines that measure parameters relating to oxygen and energetics in the body). We are already implementing this model in volunteer studies and hope to use it soon in patients on adult neurointensive care units. We further developed our model to include the role of natural modulators of CCO, in particular the gas signaling molecule nitric oxide. Our model was able to quantify how CCO interacted in two distinct ways with nitric oxide, one inhibitory and one protective to the body. We were able to show how a related oxygen consuming enzyme, cytochrome bd in the bacterium E. coli, was able to resist inhibition by nitric oxide by having a uniquely fast rate of removal of this potentially toxic gas. Nitric oxide is one of the immune systems' "weapons" in attacking bacteria such as E. coli, and the presence of this cytochrome bd enzyme seems to protect the bacteria from attack. Future research might be able to target cytochrome bd with specific drugs and kill invading bacteria, whilst not harming the human patient. |
Exploitation Route | Our biochemical/physiological model can assist in the interpretation of biological and clinical real time spectroscopic data on patients and animal models. The re-evaluation of the spectroscopic signals allows for more detailed interpretation of current in vivo data, and allows for the possibility of new measurement modalities. We have identified a key bacterial enzyme that targets the host defence mechanisms - this has the potential to be a new target for new antibiotics. |
Sectors | Healthcare |
URL | http://www.ucl.ac.uk/medphys/research/borl/nirs/nirs/current_projects/math_physio_model |
Description | Our biochemical/physiological model has been used in ongoing animal and clinical research. It is being developed for clinical use, initially in neurointensive care. However, it is still too early for there to be an impact in patient care. |
First Year Of Impact | 2008 |
Description | Leverhulme Trust Research Grant |
Amount | £208,935 (GBP) |
Funding ID | F/00 213/T |
Organisation | The Leverhulme Trust |
Sector | Charity/Non Profit |
Country | United Kingdom |
Start | 03/2011 |
End | 03/2013 |
Description | Wellcome Trust Project Grant |
Amount | £228,997 (GBP) |
Funding ID | 0899144 |
Organisation | Wellcome Trust |
Sector | Charity/Non Profit |
Country | United Kingdom |
Start | 05/2009 |
End | 05/2012 |
Title | Modelling of brain blood flow and metabolism |
Description | We have developed BRAINSIGNALS: an open-source computational model of brain blood flow and metabolism focusing on optically-detectable signals. |
Type Of Material | Model of mechanisms or symptoms - human |
Year Produced | 2008 |
Provided To Others? | Yes |
Impact | Other researchers have expanded the model to the new born human brain and are using it for clinical research in neonatal intensive care. |
URL | http://www.medphys.ucl.ac.uk/braincirc/download/repos/NIRSmodel.html |
Description | Appearance and adviser on the Radio 4 program The science of seasonality - BBC Radio 4 Leading Edge |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Media (as a channel to the public) |
Results and Impact | As for all media activity this is hard to measure other than by noting the "approximately) 1 million viewing figures. Hard to tell for a radio 4 program. |
Year(s) Of Engagement Activity | 2009 |
URL | http://www.bbc.co.uk/programmes/b00l1rxx |
Description | Appearance on BBC 2 Horizon program How to kill a human being: the science of killing |
Form Of Engagement Activity | A press release, press conference or response to a media enquiry/interview |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Media (as a channel to the public) |
Results and Impact | My interview on the nature of gas inhibition of mitochondria (as occurs in death by cyanide poisoning) featured in a number of online comments and newspaper reviews about the program The impact in the UK was minor as we have no death penalty. In the US it informed part of the (of course) much wide debate about the ethics and legality of how to kill a human being on death row. |
Year(s) Of Engagement Activity | 2009 |
URL | http://www.bbc.co.uk/sn/tvradio/programmes/horizon/broadband/tx/executions/ |
Description | BBC Health Web pages |
Form Of Engagement Activity | A magazine, newsletter or online publication |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Media (as a channel to the public) |
Results and Impact | Press release was a feature on the BBC health web pages The web page was liked to from a variety of national and international web sites |
Year(s) Of Engagement Activity | 2008 |
URL | http://news.bbc.co.uk/1/hi/england/7797013.stm |