Horace Albert "Nook" Barker 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. He was recognized with the National Medal of Science for his role in identifying an active form of Vitamin B12. Barker was born on November 29, 1907 in Oakland, California. He attended Stanford University, graduating in 1929 with a bachelor's degree in physical science, and was awarded a Ph.D. in chemistry in 1933. Barker died at age 93 on December 24, 2000, due to heart failure at his home.