whence Coomassie?

[Ed Rybicki]

> BI1RGW at ibm.shef.ac.uk writes:
> > Hello Netland.
> >
> > Can anyone remind me of the details of what, how and when Coomassie R/G bind
> > to proteins?  As I recall, R binds slower but is more sensitive - but what do
> > they bind?  I have at the back of my mind some vague inkling about lysine
> > residues - but what about arginine, and what about the N-terminus?
> >
> > I'm sure this is a FAQ, but...all comments, recollections, anecdotes welcome.
>
>     You know, I spent a little bit of time researching just what exactly Coo-
> massie dye binds to.  The basic conclusion that I reached at the time was
> that either nobody knows, or I was looking in the wrong places.  There is a
> whole chapter on various anionic dyes in a 1985 book on electrophoresis, but
> as I remember it, other than a lot of interesting stuff about the history and
> some explanations of sensitivity and a good bit of detail about linearity of
> staining intensity to mass of protein, there wasn't much about binding.  All
> I remember was that Coomassie was supposed to bind free amino groups.  Of
> course, that would dictate lysine binding, but I got the impression the in-
> teraction between dye and protein wasn't that specific.
>
>     I'd be a little surprised if this were a FAQ, but if it is, or if there
> are any dye organic chemists out there chomping at the bit to enlighten this
> cell biologist who's out of his league, I'd be interested.

I think you may find it actually binds the peptide bond - there are a lot
of proteins with no free lysine which bind CBB just fine (like tobacco
mosaic virus coat protein).  I recall writing an essay on protein
quantitation some time in '77 where that was the received wisdom - but I'm
buggered if I can remember a reference, and the essay got thrown out a
while back....

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