Peter Mitchell was born in 1920 in Surrey, with his father working as a civil servant. He pursued a study of the natural sciences, specializing in biochemistry, at various institutions including Queen’s College and Cambridge. At the age of 22, he was given a research post at Cambridge and would eventually earn a PhD in 1951 for his work on penicillin’s mode of action.
Through his work, Mitchell realized that the movement of ions across an electrochemical potential difference would have the ability to provide the energy that was needed to produce ADP. Living cells having a membrane potential and an interior negative to the surrounding environment was well known at the time. He also believed that the movement of these ions could be affected by thermodynamic forces.
This would become the foundation for what would eventually become the Chemiosmotic theory.
What Is the Chemismotic Theory?
In 1961, Mitchell proposed what would be called the chemiosmotic hypothesis. It is a theory which states that adenosine triphosphate, or ATP, synthesis in a respiring cell comes from the electromechanical gradient that is found across the inner membrane of mitochondria. It uses the energy of nicotinamide adenine dinucleotide (NADH) and the Flavin group, which is a group of organic compounds that is based on pteridine.
The energy is formed when glucose or other energy-rich molecules are broken down by the body.
When energy-rich molecules are metabolized, they produce an intermediate energy source that is equally rich. This is then coupled to the reduction of a carrier molecule within the mitochondrial matrix in order to pass electrons through the inner mitochondrial membrane and the to proteins within the electron transport chain.
This energy found within the electrons is then used to pump protons throughout the mitochondrial matric to store energy. The protons then move back across the membrane through the ATP synthase enzyme. This energy forms with inorganic phosphates to synthesize ATP. As a final step, the protons and electrons at the last stop of the electron transport chain are taken up by oxygen molecules and this forms water.
What Was the Initial Reaction to the Chemiosmotic Theory?
When Mitchell first proposed the Chemiosmotic theory, it was a fairly radical proposal. The scientific community did not accept it very well. At the time, the energy from electron transfers was believed to be stored as a stable high potential intermediate. This was a more conservative concept, but it was also a problematic belief because no one had ever been able to find high energy intermediates throughout their research.
Over the next decade after Mitchell proposed the theory, the evidence that proton pumping complexes existed in the electron transfer chain grew to the point where it could no longer be ignored by the scientific community. In 1978, Mitchell was awarded the Nobel Prize in Chemistry for his work that was first proposed 17 years before.
How the Chemiosmotic Theory Changed Science
In the 1960s, the ideas of cell function and electron transfer were generally known, but there were no specifics or mechanisms that had been discovered or theorized about at the time. Having electron transfer coupled to ATP synthesis through oxidative phosphorylation and photophosphorylation was unknown. Several hypotheses existed, but before Mitchell, most looked at a direct chemical interaction.
Several laboratories had been performing extensive research on the subject, but no experimental evidence of the hypotheses that were generally accepted at the time could be produced. When Mitchell proposed that ATP synthesis was based on an indirect interaction between oxidizing and phosphorylating enzymes, and with ongoing research, the basic postulates from his original hypothesis turned out to be correct.
The goal of the Chemiosmotic theory is not to iron out the details of the underlying molecular mechanisms that are in play. It is simply to create the foundation to explore the mechanisms that are involved in phorylation. By understanding how biological power transmission occurs, we can understand more about the energy requirements of other cellular processes, including how nutrient uptake occurs.
This theory opened up an entire field of research that is known as “bioenergetics.” A number of technologies exist today because of this initial hypothesis. It has helped us to understand energy-transfer systems, allow us to refine the efficiency of solar and fuel-cell systems, and know the process behind motion and heat production from a biological perspective.
Peter Mitchell passed away in 1992, but not before he saw his life’s work continue to evolve and influence the scientific community. His theory continues to provide the foundation for bioenergetics research to this day.