Horace Albert "Nook" Barker (November 29, 1907 – December 24, 2000) was an American biochemist and microbiologist who studied the operation of biological and chemical processes in plants, humans and other animals, including using radioactive tracers to determine the role enzymes play in synthesizing sucrose.
[1] After graduating from Stanford, he performed a two-year postgraduate fellowship at the Hopkins Marine Station under the supervision of microbiologist C. B. van Niel, who fostered Barker's interest in botany and taught him techniques for isolating microorganisms.
He was part of a team that developed the use of Carbon-14 as a radioactive tracer, using the technique in 1944 to show how sucrose is synthesized in living cells by enzymes.
[2] Research led by Barker during the 1950s provided insights into the uses of vitamin B12 in the body using bacterium he had isolated from mud taken from San Francisco Bay.
[2] In a White House ceremony held on January 17, 1969, U.S. President Lyndon Johnson awarded Barker with the National Medal of Science "[f]or his profound study of the chemical activities of microorganisms, including the unraveling of fatty acid metabolism and the discovery of the active coenzyme form of vitamin B12.