Struggling US brokerage firm MF Global filed for bankruptcy Monday, as trade in its shares was halted on the New York Stock Exchange and the firm was frozen out by regulators. The derivatives broker -- which at one time held approximately $41 billion in assets -- was hit by a string of losses related to Europe\'s debt crisis. The Financial Times and the Wall Street Journal reported the firm was to issue the filing as part of a plan to sell off assets to Interactive Brokers Group. On Monday the trade in shares was halted on the New York Stock Exchange as the New York Federal Reserve announced MF Global was \"suspended from conducting new business with the New York Fed.\" That would continue \"until MF Global establishes, to the satisfaction of the New York Fed, that MF Global is fully capable of discharging the responsibilities.\" While MF Global is well-known on Wall Street, it is not thought to be so interconnected that its collapse could trigger a crash like that seen in the wake of the Lehman Brothers bankruptcy in 2008. If it collapses, however, it would be \"the biggest US casualty so far in the European sovereign crisis,\" according to Chris Low of FTN Financial. \"Hopefully, the firm\'s situation is unique. (Chief executive Jon) Corzine\'s bet on sovereign debt is what got the firm in trouble. According to regulators, other, bigger US entities are not exposed.\"