Macquarie Group may remain in the hunt for some of the assets of the commodities trading business RSS Sempra after JP Morgan got cold feet in recent days, with the latter's rethink influenced by the risk of new US restrictions on proprietary trading by banks.British bank RBS is acting under orders from the European Union to dispose of its 51 per cent stake in RSS Sempra, while Sempra, its joint venture partner, is also selling out.Macquarie was on the short list for RSS Sempra, worked out in late 2009.JP Morgan may still buy the European operations of Sempra, the Financial Times and Wall Street Journal reported.That may leave the US commodities and energy trading business up for sale. Deutsche Bank was the other under-bidder along with Macquarie, if past media reports are any guide.An energy investment banking theme has emerged in Macquarie's purchase of new businesses in the northern hemisphere over the last year, though the original interest in RSS Sempra, if true, looked a significant financial stretch for the group, given a price tag of well in excess of US$3 billion.