Theresa Villiers is now the shadow secretary of state for transport, Peter Ainsworth becomes shadow secretary of state for the environment, food and rural affairs and Alan Duncan is responsible for business, enterprise and regulatory reform.
"These changes strengthen the shadow cabinet team and harness new talent within the party as we prepare for the next general election," Mr Cameron said.
Meanwhile, Brown has made further appointments.
Two new ministers have taken up positions in the Department for Transport, joining new secretary of state for transport Ruth Kelly and rail minister Tom Harris.
Rosie Winterton, member of parliament for Doncaster Central since 1997, has been appointed minister of state while Jim Fitzpatrick, MP for Poplar and Canning Town, has become under secretary of state for transport.
Mrs Winterton was previously a minister at the Department of Health. Mr Fitzpatrick worked in the London Fire Brigade until 1997 when he was elected as MP for the east London and Docklands constituency.
The new ministers will take over the responsibilities of Dr Stephen Ladyman and Gillian Merron, who has been handed a new role in the Cabinet Office.