After the death of her husband Anton Penizek (1868–1937), Melanie Penizek took over the antiques dealership established in 1934 at Spiegelgasse 19 in Vienna's 1st district and continued it initially as his widow. In 1949 she obtained her own trade licence to deal in antiques at the new location at Spiegelgasse 8. The art dealerships belonging to Karl Löscher and Anton Jancsy were also located at this address. Little is known of Penizek's business dealings. Between 1939 and 1944 she is listed as a consignor to the Viennese auction house Adolf Weinmüller. There were also sales to the "Sonderauftrag Linz" in 1944. From 1938, several museums and collections made purchases from her. In 1938, for example, she sold a work by Albin Egger-Lienz to the city of Lienz, in 1939 and in the early 1950s miniatures to the Albertina, and porcelain to the Österreichische Museum für angewandte Kunst (Austrian Museum of Applied Arts) in the 1940s and 1950s. She gave up her trade licence in 1965, after which the business was closed.