The bank's stock showed a loss of 8.12 percent to €41.12 while the DAX index of leading shares was 0.84 percent lower overall.
Deutsche Bank said on Tuesday that it would book a loss in the third quarter of its fiscal year stemming from its purchase of Postbank.
On Wednesday, Deutsche Bank launched a capital increase of €10.2 billion ($13.6 billion), its biggest ever, to pay for the acquisition of up to 30.6 percent of the shares in Postbank, which has Germany's biggest retail bank network.
Deutsche Bank will offer €25 per share for this holding.
The subscription for the Deutsche Bank share offer runs from Wednesday to October 5, with the new stock to be listed in Frankfurt and New York from October 6.
Deutsche Bank already owns nearly thirty percent of Postbank and the deal will see it strengthen its retail operations and so balance its current focus on investment bank activities.
Comments made Tuesday about third-quarter results in its rights issue prospectus were interpreted as a surprise profit warning, Merck Kinck analyst Konrad Becker said.
As the result of a separate deal, Deutsche Bank is set to acquire the remaining equity in Postbank from German logistics group Deutsche Post in several steps in 2012-2013 at an already agreed price of €45 per share.