Catalyzes the o-hydroxylation of 3-hydroxy-9,10-secoandrosta-1,3,5(10)-triene-9,17-dione (3-HSA) to 3,4-dihydroxy-9,10-secoandrosta-1,3,5(10)-triene-9,17-dione (3,4-DHSA) in the catabolism of cholesterol. Can also use 3,17-dihydroxy-9,10-seconandrost-1,3,5(10)-triene-9-one (3,17-DHSA), but it has higher specificity for 3-HSA than for 3,17-DHSA. Can use either FADH(2) or FMNH(2) as flavin cosubstrate. Also catalyzes the o-hydroxylation of a range of p-substituted phenols to generate the corresponding catechols. 3-hydroxy-9,10-secoandrosta-1,3,5(10)-triene-9,17-dione + FMNH2 + O2 = 3,4-dihydroxy-9,10-secoandrosta-1,3,5(10)-triene-9,17-dione + FMN + H(+) + H2O 3,17-dihydroxy-9,10-secoandrost-1,3,5(10)-triene-9-one + FMNH2 + O2 = 3,4,17-trihydroxy-9,10-secoandrost-1,3,5(10)-triene-9-one + FMN + H(+) + H2O Lipid metabolism; steroid biosynthesis. Homotetramer under anaerobic conditions. HsaAB monooxygenase consists of an oxygenase component HsaA and a reductase component HsaB. Induced by KstR. Cholesterol metabolism contributes to the survival of M.tuberculosis in the host by helping the bacterial multiplication during earlier stages of infection and to the dissemination of the pathogen in the host. Belongs to the HpaH/HsaA monooxygenase family.