Phosphoserine phosphatase (SerB), (<db_xref db="EC" dbkey="3.1.3.3"/>), also known as O-phosphoserine phosphohydrolase, is involved in both serine and glycine biosynthesis. It catalyzes the reaction 3-phospho-serine + H2O = L-serine + phosphate, which is the last step in the biosynthesis of serine from carbohydrates. The reaction proceeds via the formation of a phosphoryl-enzyme intermediate. It acts as a homodimer, and requires magnesium as a cofactor.