Alpha subunit of the oxygenase component of the 2-aminobenzenesulfonate 2,3-dioxygenase system (deaminating) (ABSDOS). Can use 2-aminobenzenesulfonate (ABS), benzenesulfonate (BS), 4-toluenesulfonate (TS), 2-nitrobenzenesulfonate, 3- and 4-aminobenzenesulfonates, 4-chloro- and 4-hydroxybenzenesulfonates and pyridine-3-sulfonate as substrates. No desulfonation of ABS to aminocatechol or aminophenol detected. 2-aminobenzenesulfonate + 2 H(+) + NADH + O2 = 2,3-dihydroxybenzenesulfonate + NAD(+) + NH4(+) Binds 1 [2Fe-2S] cluster per subunit. Binds 1 Fe cation per subunit. Inhibited by o-phenanthroline. Optimum pH is 7.5. Optimum temperature is 35 degrees Celsius. Heterotetramer with a alpha2beta2 structure. Part of the abs operon that is induced during growth with 2-aminobenzenesulfonate (ABS) as carbon source. Belongs to the bacterial ring-hydroxylating dioxygenase alpha subunit family.