Where does energy for tail sheath contraction come from?

Since virus does not generate energy on its own, we are confounded by how the tail sheath contract. (out of syllabus)



One school of thought:

Hydrolysis of ATP stored in tail sheath upon conformation change.
(mentioned in this paper http://jb.asm.org/cgi/content/full/183/1/358)


Another school of thought:

There is a conformation change that involves a change in energy states (high to low) when the tail sheath contracts, thus favorable.

http://72.14.235.104/search?q=cache:fvBMMNlafq8J:bilbo.bio.purdue.edu/~viruswww/Rossmann_home/publ/pdfs/425.pdf+contraction+of+tail+sheath+energy&hl=en&gl=sg&ct=clnk&cd=9

Interesting.