– SULT1A3 belongs to the sulfotransferase 1 family. Sulfotransferase enzymes catalyze the sulfate conjugation of many hormones, neurotransmitters, drugs, and xenobiotic compounds. They are different in their tissue distributions and substrate specificities while their gene structure (number and length of exons) is similar. SULT1A3 gene encodes a phenol sulfotransferase with thermolabile enzyme activity. Four sulfotransferase genes are located on the p arm of chromosome 16; this gene and SULT1A4 arose from a segmental duplication. It is the most centromeric of the four sulfotransferase genes. Exons of this gene overlap with exons of a gene that encodes a protein containing GIY-YIG domains (GIYD1). SULT1A3 is expressed in liver, colon, kidney, lung, brain, spleen, small intestine, placenta and leukocyte. SULT1A3 is a sulfotransferase that utilizes 3′-phospho-5′-adenylyl sulfate (PAPS) as sulfonate donor to catalyze the sulfate conjugation of phenolic monoamines (neurotransmitters such as dopamine, norepinephrine and serotonin) and phenolic and catechol drugs.