Teachers' Retirement System of Oklahoma, Oklahoma City, hired JPMorgan Worldwide Securities Services to replace Northern Trust as the $8.2 billion plan's global custodian, confirmed CIO William Puckett. Plan officials issued an RFP in the spring of 2005. The contract with Northern Trust expired last year but was extended. The change was not because of Northern Trust's performance, Mr. Puckett said. Gregory.w.group assisted.