Why "alanine" scanning?

[Ian A. York]

My boss just asked me this, and I didn't have a very satisfactory answer: 
Why, when doing alanine scanning, does one change to alanine instead of
glycine?  I understand that alanine is sort of a generic, unexciting, Joe
Amino Acid; but why isn't glycine just as bland, boring, and unexciting?

I mumbled about maybe having a sidechain made alanine a little more
generic than glycine, but I couldn't come up with a clear justification.
Anyone?

Ian
-- 
      Ian York   (iayork at panix.com)  <http://www.panix.com/~iayork/>
      "-but as he was a York, I am rather inclined to suppose him a
       very respectable Man." -Jane Austen, The History of England