Arcandor owns a majority stake in Thomas Cook - but tried to assure customers that the travel company would not be affected by today's setback.
Bosses said the court filing covered its Karstadt department stores, Primondo GmbH mail-order and Quelle catalogue businesses but excluded Thomas Cook, which is Europe's second-largest travel group.
Thomas Cook insisted it was "business as usual" and reassured holidaymakers they would not be affected by Arcandor's insolvency move.