Catalyzes the oxidation of sulfite to sulfate, the terminal reaction in the oxidative degradation of sulfur-containing amino acids (By similarity). Can run in reverse direction and reduce nitrite to nitric oxide under physiologically relevant conditions, such as hypoxia (PubMed:41337830). {ECO:0000250|UniProtKB:P07850, ECO:0000269|PubMed:41337830}. This is the function of SUOX (sulfite oxidase, Ensembl gene identifier ENSG00000139531).