The two firms reported on Wednesday that the deputy president of the ANC, Ramaphosa, will be quitting the boards.
Ramaphosa was elected ANC president Jacob Zuma's deputy at the party's 53rd national conference in Mangaung in December and said at the time he would consequently be reviewing his various business interests.
The former anti-apartheid mining union leader, who quit politics in 1997 to further his business interests, is one of Africa's richest men and sits on the boards of some of the continent's biggest companies.
He also sits on the board of Standard Bank and brewer SAB Miller.
Ramaphosa is expected to become South Africa's deputy president after national elections in 2014, teeing him up as a possible head of state should the ANC win elections five years later.
At the start of the year, Ramaphosa – a respected board member of Lonmin, which owns the Marikana mine where 34 workers were killed by police in 2012 – claimed his email call for action against the miners and their subsequent death was not linked.
During the course of the Farlam commission of inquiry into the killings, it was revealed that Ramaphosa sent emails to government ministers and Lonmin management asking for action against the protesting miners.
"Basically all it boils down to is that prior to the killing of the 34 people by police guns, 10 people had died and some of them had died in the most brutal way," he told CNN host Christiane Amanpour in an interview.
"They had died in what I still see as a 'criminal' way … I was appealing to the authorities to take action to prevent further deaths," added Ramaphosa, who was the first general secretary of the National Union of Mineworkers and chaired the Constitutional Assembly in 1994. – Reuters