Hemoglobin

 Click-hold mouse button to move structure.
Click "x" box to toggle between structures
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  to optimal view   Heme-Fe/ Ball&Stick
  Spacefill / wireframe   Heme-O2/ Ball&Stick
  Backbone / Ball&Stick   Heme-His/ Ball&Stick
  Polar / wireframe   Non-Polar / wireframe

Color Codes

C

 H

 N

 O

 P

 S

 Cl

 F
Ribbon / Ball&Stick