Sulfotransferase 1A3/1A4 (SULT1A3) is 295 amino acids in length and localizes to the cytoplasm. It is a member of the Sulfotransferase 1 family. SULT1A3 can be found in the liver, colon, kidney, lung, brain, spleen, small intestine, placenta, and leukocytes. SULT1A3 exists as a homodimer and it catalyzes the sulfation of phenolic monoamines, such as dopamine, norepinephrine and serotonin, and phenolic and catecholic drugs.