Involved in the biosynthesis of the indolocarbazole antitumor agent rebeccamycin. It generates the imine form of 7-chloroindole 3-pyruvate (7Cl-IPA) from 7-chloro-L-tryptophan (7Cl-Trp), with concomitant two-electron reduction of O(2) to H(2)O(2). The enzyme is also active with L-tryptophan as substrate. 7-chloro-L-tryptophan + O2 = 3-(7-chloroindol-3-yl)-2-iminopropanoate + H2O2 L-tryptophan + O2 = 2-iminio-3-(indol-3-yl)propanoate + H2O2 kcat is 12.12 min(-1), 1.53 min(-1), 14.32 min(-1), and 39.82 min(-1) for L-tryptophan, 1-methyl-L-tryptophan, 5-fluoro-L-tryptophan and 7-chloro-L-tryptophan, respectively (at pH 7.8). Homodimer. Belongs to the flavin monoamine oxidase family. RebO subfamily.