Nick Clegg has said the government showed its strength in the way it reacted to David Laws' resignation.
The deputy prime minister said the coalition "acted very fast" to name Danny Alexander as his successor as Chief Secretary to the Treasury.
He said Mr Alexander could handle the "political balancing trick" involved in the job and making the coalition work.
Insisting government was carrying on as normal he also pledged support for English regions facing spending cuts.
He told the Independent that regions heavily reliant on public sector jobs would not be left "high and dry" by looming public sector cutbacks, the first of which were announced earlier this month.
There would extra government assistance for areas of the north-east, north-west, South Yorkshire and London as well as incentives for business to take on staff.
Ministers are still dealing with the fallout from Mr Laws' decision to stand down over his expenses claims.
Mr Alexander's switch from scottish secretary to take the number two role in the Treasury, which he will play a central role in cutting government spending, has surprised some.
Critics say the job was always earmarked for a Liberal Democrat, irrespective of their qualifications, to tie the party into difficult spending decisions and to maintain the coalition's stability.
But Mr Clegg rejected suggestions Mr Alexander - his former chief of staff and one of those who negotiated the parties' coalition agreement - was not a natural choice for the role.
"I just don't agree with that and David Cameron does not agree with that either othwerwise the decision would not have been taken to appoint Danny Alexander," he told Today.
"He has been appointed to that position because the view is he is genuinely the best person," he said, adding that we was "extremely gifted and able".
"He will work very well with George Osborne. He understands how the coalition works so to make sure that as we are entering into this very difficult period of fiscal contraction, we also honour the things that the coalition government has pledged to do.
"I think that is a very difficult political balancing trick. I think he is ideally placed to do that."
Asked whether fundamental differences between the two parties were already showing themselves, Mr Clegg acknowledged the two parties did not agree on certain policy areas.
But he said this would not undermine its central ambitions and was "excited" by the values that united the two sides and would shape their policy agenda.
"Whilst money is tight each and every single person in this coalition, from whatever party they come from, are dedicated to increasing social mobility and social opportunity for everybody in this country through the kind of reforms that Labour failed to deliver," he said.
"I think it is a Liberal agenda but also an agenda which unites the whole coaltion government."
Describing the coalition agreement as a "document of immense ambition", he said the public would see a genuinely radical approach to the environment, political reform, education and rebuilding the economy after the recession.
"I think, over time, people will see a pattern of a government that is actually strengthened by having these different philosophies and identities within it."