NEW YORK (MarketWatch) -- A run on a money market fund managed by Putnam Investments, a subsidiary of Great West Lifeco Inc. gwli has forced the company to liquidate the institutional fund. Putnam said that "significant redemption pressure" on Wednesday forced it to close the $15 billion Putnam Prime Money Market Fund ppmxx. "Constraints on liquidity in money market instruments created the risk that in order to process redemptions, the fund would realize losses in selling its portfolio securities," said Putnam in a statement. "The Trustees determined to close the fund to ensure equitable treatment of all fund shareholders." The statement did not say when shareholders will receive their money, nor did it say whether the payouts would maintain the fund's $1 a share net asset value.