The 57-year-old German-born neuroscientist, who describes himself as "incredibly driven", was in fact driving around Spain when he got a phone call on Monday to break the news that he had won the Nobel Prize.
On the other end of the line was not the friend Südhof had been expecting, but a spokesman for the Nobel Prize committee in Stockholm, Sweden.
"Are you serious? Oh, my God," Südhof said upon learning that he, along with American colleagues James Rothman and Randy Schekman, had won the 2013 Nobel Prize for Medicine. "I'm sorry. This is a little unexpected."
The trio were honoured for their work exploring how cells organize their cargo and move molecules - a process that contributes to normal body and brain function but is also at the root of neurological diseases, diabetes, and immune disorders.
Südhof was described as a "great scientist" and a "wonderful collaborator" by co-winner James Rothman of Yale University, who studies how cells transport energy outside of themselves.
The scientist was born in Göttingen in 1955 and gained his first degree in medicine from Göttingen University in 1982. Emigrating to the US the following year, Südhof has since become an American citizen and now has a lab at Stanford University in California.
"Every scientist should spend some time in another country, and countries should give them that opportunity," Südhof told Spiegel news magazine.
The work that won Südhof the world's most prestigious prize for medicine focuses on how synapses form in the brain and how messages are sent, with a view to unlocking the mysteries of Alzheimer's disease and autism.
Colleagues say his work ethic is astounding, and he is renowned for his high productivity.
"My wife thinks I am crazy," Südhof told the Nobel Committee spokesman."I don't know. I am incredibly driven. I didn't think I was when I was young. I thought I was normal. But as I get older and I see the other people around me, I feel sometimes that that is the way I am."
Like most professional scientists, Südhof has seen his share of "intellectual disagreements". For two years between 1995 and 1997, he commuted between the USA and Göttingen in order to work as a director of the Max Planck Institute for Experimental Medicine there.
But the Institute's president, Hubert Markl, didn't like Südhof's methods. "He thought the animal house I had planned was too big," he told the magazine.
Unable to work with Markl, Südhof beat a retreat back to the states. "I was very young...he didn't control me, but I wasn't confident enough, so I looked for a new job."
Yet thirty years after emigrated to the US, German-born Südhof has said he would like to return to Germany. "The landscape of research in Germany is excellent. It has a lot to offer."
"I'd really like to come back, and it would give my two kids a chance to learn the language" he said.
But however much he might want it, the move is not likely to go ahead, he said. "Career-wise I'm just too old for it. I want to keep doing research for as long as I can, and that's possible here in the USA."
Südhof's scientific aims still remain high despite the monumental award: "I want to simulate individual synapses - I want to find out why these are lost in Parkinson's disease patients."
"Science is a continuous process," he said: "It's like a medieval cathedral, gradually being built. At the end, you have something to be proud of."
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