This is the protein Hemogrobin. Hemoglobin is one of the most well known proteins, which transports oxygen in our blood. A human being has several hundred grams of Hemoglobin.  The protein consists of 4 units; two alfa chains and two beta chains. Each alfa chain consits of 141 amino acids, and each beta 146 amino acids.  

 In the Hemoglobin molecule, there are four Hemes, iron containing molecules, which actually transport oxygen.  You can see 4 green iron atoms which located inside the circular Heme molecule and each iron captures a red dioxygen molecule.  This hemoglobin is in the T state, which is unstable form, but all iron atoms in the heme molecules bind to oxygen molecule, O2.  

 The structure was reported by a group of Prof. Anthony Wilkinson of York University in 1996 (Journal of Molecular Biology, 256, 775-792). We can freeely obtain the structural data from the Protain Data Bank (http://www.rcsb.org/).  The atomic coordinate data were converted to VRML file using the Rasmol software.  After some modification of the VRML file, the 3D structure was projected by Cortona 3D web-plugin. The protein has a Donut-shaped structure, so the camera was set inside the hole and I took 30 screenn-shot pictures and stitched them into a panorama.  The color of atoms are;  green, iron; gray, carbon; blue, nitrogen;  red,oxygen; and yellow, sulfer.  The structure was analyzed by X-ray crystallography technique, so hydrgogen atoms cannot be determined.  You can see many isolated Red balls, which are oxygen atoms of water molecules.  The protein contains about 200 water molecules.