The sulfatase-modifying factor 1 (SUMF1, also called C-alpha-formylglycine-generating enzyme, FGE) (Preusser-Kunze et al. 2005, Cosma et al. 2003, Landgrebe et al. 2003) oxidises the critical cysteine residue in arylsulfatases to an active site 3-oxoalanine residue thus confering sulfatase activity (Roeser et al. 2006). Defects in SUMF1 cause multiple sulfatase deficiency (MSD) (MIM:272200), an impairment of arylsulfatase activity due to defective post-translational modification of the cysteine residue (Cosma et al. 2003, Dierks et al, 2003). This post-translational modification is thought to be highly conserved in eukaryotes (Selmer et al. 1996, von Figura et al. 1998). SUMF1 is active as either a monomer or a homodimer. A monomer is described in this reaction.