Nitrosourea synthase

UniProtKB accession:  A0A411MR89

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UniProtKB description:  Involved in the biosynthesis of the glucosamine-nitrosourea antibiotic streptozotocin (SZN) (PubMed:30728519, PubMed:30763082). Catalyzes a complex multi-step reaction: the overall reaction is an oxidative rearrangement of the guanidine group of N(omega)-methyl-L-arginine (L-NMA), generating an N-nitrosourea product (PubMed:30728519, PubMed:30763082, PubMed:32511919). SznF first hydroxylates L-NMA to form N(delta)-hydroxy-N(omega)-methyl-L-arginine (L-HMA), which is further hydroxylated to give N(delta)-hydroxy-N(omega)-hydroxy-N(omega)-methyl-L-arginine (L-DHMA) (PubMed:30728519, PubMed:32511919). Subsequently, an oxidative rearrangement converts this intermediate to N(delta)-hydroxy-N(omega)-methyl-N(omega)-nitroso-L-citrulline (PubMed:30728519, PubMed:34004115). This product is unstable, and degrades non-enzymically into nitric oxide and the denitrosated product N(delta)-hydroxy-N(omega)-methyl-L-citrulline (PubMed:30728519).