Peter D. Mitchell

Peter Dennis Mitchell (September 29 1920–April 10 1992) was a British biochemist who was awarded the 1978 Nobel Prize for Chemistry for his discovery of the chemiosmotic mechanism of ATP synthesis.

Mitchell was born in Mitcham, Surrey, England.

Biography
Peter D. Mitchell was born in Mitcham, Surrey on 29 September 1920. His parents were Christopher Gibbs Mitchell, a civil servant, and Kate Beatrice Dorothy (née) Taplin. He was educated at Queen's College, Taunton, and at Jesus College, Cambridge where he studied the Natural Sciences Tripos specialising in biochemistry.

He accepted a research post in the Department of Biochemistry, Cambridge, in 1942, and received the degree of Ph.D. in early 1951 for work on the mode of action of penicillin. In 1955 he was invited by Professor Michael Swann to set up a biochemical research unit, called the Chemical Biology Unit, in the Department of Zoology, Edinburgh University, where he was appointed to a Senior Lectureship in 1961, to a Readership in 1962, although ill health led to his resignation in 1963.

Independent researcher
From then to 1965, he supervised the restoration of a Regency-fronted Mansion, known as Glynn House, near Bodmin, Cornwall - adapting a major part of it for use as a research laboratory. He and his former research colleague, Jennifer Moyle founded a charitable company, known as Glynn Research Ltd., to promote fundamental biological research at Glynn House and they embarked on a programme of research on chemiosmotic reactions and reaction systems .

In 1978 he won the Nobel Prize in Chemistry "for his contribution to the understanding of biological energy transfer through the formulation of the chemiosmotic theory."

Chemiosmotic hypothesis
In the 1960s, ATP was known to be the energy currency of life, but the mechanism by which ATP was created in the mitochondria was assumed to be by substrate-level phosphorylation. Mitchell's chemiosmotic hypothesis was the basis for understanding the actual process of oxidative phosphorylation. At the time, the biochemical mechanism of ATP synthesis by oxidative phosphorylation was unknown.

Mitchell realised that the movement of ions across an electrochemical membrane potential could provide the energy needed to produce ATP. His hypothesis was derived from information that was well known in the 1960's. He knew that living cells had a membrane potential; interior negative to the environment. The movement of charged ions across a membrane is thus affected by the electrical forces (the attraction of plus to minus charges). Their movement is also affected by thermodynamic forces, the tendency of substances to diffuse from regions of higher concentration. He went on to prove that ATP synthesis was coupled to this electrochemical gradient.

His theory was confirmed by the discovery of ATP synthase, a membrane-bound protein that uses the potential energy of the electrochemical gradient to make ATP.

Mitchell's chemiosmotic theory turned out to be one of the two seminal discoveries in biology in the 20th century (DNA being the other).