Barker, Horace Albert: (1907-2000) American biochemist who, among other things, discovered the biologically active forms of vitamin B12. Horace Albert Barker, informally called "Nook," was educated at Stanford University and earned a PhD in chemistry in 1933. His research interest then turned to soil microbiology and microbial biochemistry. He set out on a two-year postdoctoral fellowship to study first with C. B. van Niel at the Hopkins Marine Station, Pacific Grove, California, and then a year in the Netherlands to study with van Niel's mentor, A. J. Kluyver in Delft. There he initiated an investigation that would later lead him to discover vitamin B12 coenzyme. Coenzymes are non-protein molecule that help the catalytic function of enzymes.
In 1936 Barker started his academic career at the University of California, Berkeley. Barker made major contributions to the study of bacterial metabolism, particularly in the synthesis and oxidation of fatty acids, the fermentation of amino acids and purines, and carbohydrate transformations. He was also well known for his pioneering use of radioactive carbon-14 tracers in biochemical research in the mid 1940s and for his work on the biochemical function of vitamin B12 in the late 1950s. In 1958 Barker discovered the biologically active forms (coenzyme forms) of B12 vitamins while working on the anaerobic metabolism of glutamate. Barker was also influential as a teacher and a mentor. As a student in his laboratory once wrote: "He teaches the course the way everyone imagines their favorite grandfather would do it."