Mucuk's body was found with bullet wounds outside the Hells Angels clubhouse in Wettenberg, Hesse, police report. It is not yet clear whether an exchange of fire had taken place.
There is at this stage no indication of who murdered Mucuk, who was head of the Hells Angels in Gießen.
But for years the Gießen Hells Angels, who are by and large of Turkish heritage, have been involved in a violent feud with the more established Hells Angels group from Frankfurt am Main. The feud reportedly dates back to the founding of the Gießen Hells Angels.
Two years ago the two factions became embroiled in a gunfight outside a Frankfurt club, leaving five people injured.
On Ascension Day this year, shots were fired on a busy Frankfurt square. Two men were left injured on that occasion. Police have arrested one suspect and are still pursuing another.
Hells Angels groups have been linked to organized crime in Germany and in cases of shootings in major urban centres.
State police in Hesse say there are around 700 Hells Angels members in the state who are involved in narcotics and prostitution, the Frankfurter Allgemeine Zeitung reports.
In September a man was shot dead at Kottbusser Tor, one of the centres of the Berlin drug trade, in an assassination believed to have had Hells Angels connections.
In April, meanwhile, Berlin police conducted raids on a large brothel in the city, alleging that Hells Angels bikers had illegally procured young women for the establishment in return for free admission.