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Herschel Kenworthy Mitchell (November 27, 1913 – April 1, 2000) was an American professor of
biochemistry Biochemistry or biological chemistry is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three fields: structural biology, enzymology and ...
who spent most of his career on the faculty at the
California Institute of Technology The California Institute of Technology (branded as Caltech or CIT)The university itself only spells its short form as "Caltech"; the institution considers other spellings such a"Cal Tech" and "CalTech" incorrect. The institute is also occasional ...
. He was one of many researchers interested in
vitamin B6 Vitamin B6 is one of the B vitamins, and thus an essential nutrient. The term refers to a group of six chemically similar compounds, i.e., " vitamers", which can be interconverted in biological systems. Its active form, pyridoxal 5′-phosp ...
in the early 1940s and is credited as one of the discoverers of
folic acid Folate, also known as vitamin B9 and folacin, is one of the B vitamins. Manufactured folic acid, which is converted into folate by the body, is used as a dietary supplement and in food fortification as it is more stable during processing a ...
. He later focused his research on ''
Drosophila ''Drosophila'' () is a genus of flies, belonging to the family Drosophilidae, whose members are often called "small fruit flies" or (less frequently) pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many speci ...
'' (fruit flies), in particular the genetics and biochemistry of the heat shock response.


Early life and education

Mitchell was born on November 27, 1913, in
Los Nietos, California West Whittier-Los Nietos () is a census-designated place (CDP) in Los Angeles County, California, near the San Gabriel River and the San Gabriel River (I-605) Freeway. The population was 25,540 at the 2010 census, up from 25,129 at the 2000 cen ...
. He received a bachelor's degree in chemistry from
Pomona College Pomona College ( ) is a private liberal arts college in Claremont, California. It was established in 1887 by a group of Congregationalists who wanted to recreate a "college of the New England type" in Southern California. In 1925, it became t ...
in 1936, a master's degree from
Oregon State College Oregon State University (OSU) is a public land-grant, research university in Corvallis, Oregon. OSU offers more than 200 undergraduate-degree programs along with a variety of graduate and doctoral degrees. It has the 10th largest engineering ...
in 1938, and a Ph.D. from the
University of Texas The University of Texas at Austin (UT Austin, UT, or Texas) is a public research university in Austin, Texas. It was founded in 1883 and is the oldest institution in the University of Texas System. With 40,916 undergraduate students, 11,075 ...
in 1941, where he worked with Roger J. Williams and Esmond Emerson Snell in their work on
vitamin B6 Vitamin B6 is one of the B vitamins, and thus an essential nutrient. The term refers to a group of six chemically similar compounds, i.e., " vitamers", which can be interconverted in biological systems. Its active form, pyridoxal 5′-phosp ...
and
folic acid Folate, also known as vitamin B9 and folacin, is one of the B vitamins. Manufactured folic acid, which is converted into folate by the body, is used as a dietary supplement and in food fortification as it is more stable during processing a ...
. He is recognized as a co-discoverer of folic acid, which the three scientists extracted from four tons of processed
spinach Spinach (''Spinacia oleracea'') is a leafy green flowering plant native to central and western Asia. It is of the order Caryophyllales, family Amaranthaceae, subfamily Chenopodioideae. Its leaves are a common edible vegetable consumed either f ...
. In 1943 Mitchell moved from Texas to
Stanford University Stanford University, officially Leland Stanford Junior University, is a private research university in Stanford, California. The campus occupies , among the largest in the United States, and enrolls over 17,000 students. Stanford is conside ...
to work as a research associate with George Beadle, who at the time was studying the genetics of metabolism in ''
Neurospora ''Neurospora'' is a genus of Ascomycete fungi. The genus name, meaning "nerve spore" refers to the characteristic striations on the spores that resemble axons. The best known species in this genus is '' Neurospora crassa'', a common model organ ...
'' (a fungus that served as a
model organism A model organism (often shortened to model) is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the model organism will provide insight into the workin ...
). When Beadle moved his research group from Stanford to Caltech in 1946, Mitchell moved with him, along with other research fellows such as Norman Horowitz. Trained as a chemist, Mitchell used this experience to learn about molecular genetics, which he would apply to other model organisms in his future research.


Academic career

Mitchell began his independent research career with an appointment as an associate professor of biology at Caltech in 1949 and advanced to full professor in 1953. His early research continued to focus on the genetics of ''Neurospora'', including the first biochemical demonstration of a missing
enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...
( tryptophan synthase) from a metabolically deficient ''Neurospora'' mutant.Mitchell HK, Lein J. A Neurospora mutant deficient in the enzymatic synthesis of tryptophan. J Biol Chem. 1948;175(1):481. This finding was an essential step in establishing the central idea that
gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...
s control
metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run ...
by producing (in a manner not then understood) the
enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...
s required for specific metabolic reactions. This idea came to be known as the one-gene-one-enzyme hypothesis, and later the one-gene-one-polypeptide hypothesis. He subsequently worked on the genetics of ''
Drosophila ''Drosophila'' () is a genus of flies, belonging to the family Drosophilidae, whose members are often called "small fruit flies" or (less frequently) pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many speci ...
'' (fruit flies), a widely known model organism for studying genetics and development. Using fruit flies as models, he made major discoveries in understanding the heat shock response and has been described as a "founding father" of the heat shock field. With research fellow Robert P. Wagner, Mitchell coauthored a textbook called ''Genetics and Metabolism'' in the 1950s. It was reviewed as an important guide to the then-emerging synergy between the two fields. Mitchell retired from Caltech in 1984, assuming
professor emeritus ''Emeritus'' (; female: ''emerita'') is an adjective used to designate a retired chair, professor, pastor, bishop, pope, director, president, prime minister, rabbi, emperor, or other person who has been "permitted to retain as an honorary title ...
status.


Personal life

Mitchell was an enthusiastic athlete who brought his hobby to Caltech, establishing a recreational athletic league for graduate students and managing the Caltech teams, which included students and faculty from a variety of departments, for 25 years. He was also a self-taught glassblower who used his skills to make chemistry laboratory equipment and for a time supported his family by working in a glassblowing shop. Mitchell suffered a debilitating stroke in 1990, and recovered his speech but continued to have physical difficulties and used a wheelchair thereafter. He died on April 1, 2000, after suffering a second stroke.


References

{{DEFAULTSORT:Mitchell, Herschel K. American biochemists California Institute of Technology faculty 1913 births 2000 deaths Pomona College alumni