Walker, John Ernest (1941-) is a British biochemist who was a co-recipient, with American biochemist Paul Delos Boyer, of the 1997 Nobel Prize in chemistry for their discoveries regarding adenosine triposphate (ATP) synthase, an enzyme fundamental in producing the cellular energy that drives critical physiological functions. They also shared the prize with Danish biochemist Jens Christian Skou for his related enzyme discoveries.

Walker attended St. Catherine's College, Oxford, and earned his B.A. degree in chemistry there in 1964. He remained at Oxford to do graduate research, beginning the study of peptide antibiotics the following year and receiving his Ph.D. degree in 1969. During these years, Walker began to develop an avid interest in the groundbreaking work then being done at Cambridge University in molecular biology. After spending two years at the University of Wisconsin's school of pharmacy and then three years in France, through fellowships provided by NATO and EMBO, he returned to England in 1974 to joint the Medical Research Council's Laboratory of Molecular Biology (LMB) in Cambridge.

Taking a position in the LMB's Protein and Nucleic Acid Chemistry (PNAC) division in 1974, Walker had the opportunity to interact with the many luminaries in the field who were also there, and a position that was originally intended to last only three months continued until 1998. That year he became the director of the Medical Research Council's Dunn Human Nutrition Unit, also in Cambridge.

The work for which Walker received his Nobel Prize originated in research he did under PNAC department head Frederick Sanger, who had begun to develop new methods of DNA sequencing. In the course of this research, Walker became interested in the enzymes of oxidative phosphorylation, a process that involves ATP synthesis. ATP, which was discovered in 1929, provides the energy that allows numerous critical biochemical reactions to occur within the body. These reactions produce such functions as heartbeat, nerve contractions, and the transmission of muscle impulses.

Since its discovery, scientists have worked to explain ATP's role in energy production and how it is formed in the cell. The exact structure of this molecule was not known, however, nor had the process of synthesis been confirmed.

In the early 1980's, Paul Boyer first proposed a mechanism for the formation of ATP involving an enzyme (a substance that speeds up biochemical reactions) called ATP synthase. Walker and his team at the Medical Research Council (MRC) in Cambridge, England, spent 16 years analyzing the structure of this enzyme using chemical methods and advanced techniques involving X rays. Walker published his results in 1994, providing a molecular basis for Boyer's theoretical work. Scientists believe that this new knowledge of the energy conversion process will improve understanding of the process of aging and a number of diseases of the nervous system.

Today, still at Dunn, Walker oversees numerous areas of research. Among other endeavors, he has combined traditional methods of studying nutrition with genetic, cellular, and molecular approaches, to study human nutritional processes and thereby address specific nutritional problems. He is also engaged in applying mass spectrometric methods, a longstanding interest of his, to various investigations in proteomics, the branch of molecular biology that deals with the study of the set of proteins expressed by an organism and related processes.

Walker received the A.T. Clay Gold Medal in 1959, the Johnson Foundation Prize of the University of Pennsylvania in 1994, the CIBA Medal and Prize of the Biochemical Society in 1996, the Peter Mitchell Medal of the European Bioenergetics Congress in 1996, and in 1997 he received the Gaetana Quagliariello Prize for research in mitochondria from the University of Bari, Italy. He is a member of the Royal Society of London and and has published numerous papers in scientific journals. He was knighted in 1999.