SULT4A1 (Cytosolic Sulfotransferase 4A1; also BR-STL1/Brain sulfotransferase-like protein) is a 33-36kD member of the sulfotransferase 4 family of enzymes. SULT4A1 message is widely expressed. However, it appears to be translated only in brain. SULT4A1 is very unusual in that it is the only SULT that shows minimal activity on synthetic laboratory substrates. Instead, it acts on catecholamines and T4 in a manner that may not involve sulfonation. Human SULT4A1 is 284aa in length. A weak PAPS binding site is found between aa246-254. There are two potential isoforms, one that shows a 13aa substitution for aa248-284, and a second that contains a 48aa substitution for aa202-247. Full-length human SULT4A1 is 98% aa identical to mouse SULT4A1.