Blackstone and several other companies have replaced Knight Capital as the designated market maker for certain securities on the New York Stock Exchange, because of potential conflicts of interest arising from the trading firm taking on new backers.

The NYSE ordered that some securities be reassigned to other market making firms because Knight's new investors - a consortium including Jefferies, Blackstone and trading firm Getco - had common ownership or business relationships with some of the issuers of those securities, according to a person familiar with the move by the exchange.