Continuing from the previous tutorial ... (in other words, the file mbco.pdb is loaded and viewed in a reasonable representation).
There are two other myoglobin structures included in the VMD \ release, also compliments of Joel Berendzen. The three files are the structures reported in Nature, v. 371, Oct. 27, 1994 on page 808. The first, mbco.pdb is the structure of CO bound to the myoglobin, the second star.pdb is the intermediate photodissociated state with the CO in the distal heme pocket, and the third, deoxy.pdb, is the unligated structure.
You can make an animation of the three states using the Edit and Animate forms. Open the Edit form using the button bar and click on the Read button in the buttom right. Select the file star.pdb, and press the Ready button to load it. Repeat the process, but this time select the file deoxy.pdb. Now you have loaded three frames showing different states of the same molecule.
Open the Animate form from the button bar and press the button that looks like >>, to play the animation. Use the slider at the bottom of the form to change the speed of playback. By rotating the molecule you should get an idea of how the system changes during photodissociation.