Model of Human cytochrome c based on the Protein Data Bank entry 3ZCF:
http://www.rcsb.org/pdb/explore/explore.do?structureId=3zcf

"Cytochrome c is a component of the electron transport chain in mitochondria. The heme group of cytochrome c accepts electrons from the bc1 complex and transfers electrons to the complex IV. Cytochrome c is also involved in initiation of apoptosis."
-http://en.wikipedia.org/wiki/Cytochrome_c
STL file created using VMD:
http://www.ks.uiuc.edu/Research/vmd/
The protein backbone is represented in "cartoon" form. The heme group and residues ligating the heme iron are represented as spheres.

Successfully printed by a Replicator 2 in PLA using MakerWare(TM) 2.4.1.24, standard resolution (3 shells, 25% infill), with raft and supports.