MOLECULAR-CLONING OF RAT-LIVER SULFITE OXIDASE - EXPRESSION OF A EUKARYOTIC MO-PTERIN-CONTAINING ENZYME IN ESCHERICHIA-COLI

The cDNA encoding sulfite oxidase has been cloned from a rat liver cDN A library. The gene contains a single open reading frame of 1464 nucle otides encoding a protein of 488 amino acids. The deduced amino acid s equence contains a 22-residue amino-terminal presequence that may serv e as a mitochondrial targeting signal. The amino acid sequence deduced from the cDNA shows significant similarity to those of sulfite oxidas e from chicken liver and nitrate reductases from algal, fungal, and pl ant sources. Two cysteine residues are conserved in all of these prote ins, and it is proposed that one or both of these cysteines serve as l igands to molybdenum. The gene has been expressed in Escherichia coli to a level equivalent to that observed in rat liver. The recombinant e nzyme has been found to contain the molybdopterin form of the molybden um cofactor and is active as determined by the sulfite dependent reduc tion of cytochrome c.