Proteins for amino acid storage purposes

Didier Gauthier gauthid at
Wed Feb 28 11:53:18 EST 1996

I teach a fourth year course of metabolism. In the chapter on amino acid
(AA) biosynthesis, I told my students that proteins do not serve for amino
acid storage. Of course proteins (mainly digestive and muscular) can be
degraded into AA which carbon squeleton can be used as fuel. But this
process is not a regular feature of amino acid metabolism and is relied
upon only in "times of need" when other energy sources are hardly
available. Proteins are synthesized for specific structural or functional
roles, not merely for AA storage. Moreover there is no known form of
storage for AA (as glycogen for glucose, or triglycerides for fatty
acids). Autotrophs synthesize AA only on demand while heterotrophs degrade
any excess in their diet. All the biochemistry textbooks as well as
reviews I have consulted support one or both of these statements and do
not refute any of them. 

But one of my student came up with a medical physiology book (Guiton 8th
ed., sorry I don't remember the page) that clearly and explicitly stated
that cells synthesize some proteins for AA storage purpose. This student
also said that she read a similar statement in another physiology text. I
know that textbooks maybe wrong or confusing at times, but this concept
was so developped (not a mere sentence lost in the middle of the text)
that I am surprised.

What is the current wisdom on this issue ? Is Guiton, otherwise and
excellent human physiology textbook, wrong on this  ?

You can mail your comment directly to me, I will post a recapitulative
follow up in two ot three weeks...that is if this topic generate any

Thank you !

Didier Gauthier
Universite de Moncton    Fax: (506) 858-4355
Moncton, NB, E1A 3E9     E-mail: gauthid at

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