Jon Corzine's risk appetite helped destroy his firm. It also provided an object lesson for Paul Volcker's campaign against proprietary trading on Wall Street.

Nineteen months after former New Jersey Governor Corzine became chairman and chief executive officer, MF Global Holdings Ltd. yesterday filed for bankruptcy. Corzine's decision to boost risk-taking, including a $6.3 billion wager with the firm's own money on European government debt, triggered the collapse.

Volcker, a former Federal Reserve chairman, pushed to curb wagering by financial firms that have federal guarantees or are so entrenched in markets that they're deemed too big to fail. Regulators and the industry are wrestling over the fine print in the so-called Volcker rule, which takes effect in 2012. Now, three years after Lehman Brothers Holdings Inc. failed, MF Global's implosion and a probe into whether client money is missing may buttress the argument for tighter trading limits.