Dear Weii,
Trybutylphosphine, and its more volatile, odiferous, and allegedly
pyrophoric cousin, triethylphosphine, are, indeed, incompatible with
iodoacetamide or iodocaetic acid (or alkyl halides in general), as they
will react to form alkylphosphonium salts. So the reducing agent must
either be removed prior to alkylation, which might result in some of
the dislufides reforming, or one must use a large excess of the
alkylating agent in order to react all the alkylphosphine present
before any sulfydryl groups can be alkykated, which is messy. Hence the
recommendation for using vinyl pyridine, which alkylates cysteines
readily and is not incompatible with alkylphosphines, and also gives
one a useful chromophore (and often a useful MS/MS tag, as well) on the
cyeteine. I have no experience with using acrylamide, other than having
noted inadvertent cysteine alkylation in proteins analyzed by PAGE
under reducing conditions, as has been reported in the literature.
Ioannis Papayannopoulos
AstraZeneca
(Still in) Worcester, MA
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