Wall Street is losing one of its highest-ranking female executives.

Morgan Stanley announced that its co-president Zoe Cruz, who had been with the investment bank for 25 years, is stepping down. Her departure puts an end to speculation that she would be named successor to chief executive John Mack.

Robert Scully, who shared the post with Cruz, was named to the newly created position of office of the chairman. He will continue to report to Mack and will focus on key clients "with a particular emphasis on global sovereign investors," according to a statement. That appointment comes the same week that a sovereign investor in Abu Dhabi made a major investment in Citigroup.

Mack appointed Walid Chammah and James Gorman as the bank's new co-presidents. Chammah, who was most recently running Morgan Stanley's international businesses, will remain in London. Gorman, who is best known for building up Merrill Lynch's brokerage business, was recruited to the investment bank in 2006 to help it turn around its retail operations.

Additionally, Michael Petrick was picked to oversee Morgan Stanley's trading business and serve as co-president of institutional sales, while Neal Sheer was named head of the commodities business.

"We see significant opportunities to build on the market leadership positions we have across our global franchise and to take advantage of the strong foundation we've put in place in recent years," Mack said in a statement. "Today's markets, however, are changing rapidly, and we're putting in place a leadership team that is ideally suited to help Morgan Stanley realize the opportunities ahead, while continuing to navigate the current challenging conditions."

Cruz is just the latest high-profile departure as banks continue sorting through the mess from the subprime mortgage meltdown and the credit crisis. In recent weeks, Citigroup ousted its chief executive Charles Prince, and Merrill Lynch replaced its C.E.O. Stan O'Neal with former New York Stock Exchange head John Thain.

In September, Morgan Stanley posted its first quarterly decline since Mack took the helm. It expects to release its fourth quarter results in mid-December.