loss of analyte due to adsorption to surfaces
becomes critical when handling sub-picomole
amounts of proteins. Thus, it is required to limit
the number of steps involving lyophilization and
transfer of the sample. The application of proteases
immobilized on a solid support has several
benefits, as has been reported earlier by other
groups [6-81. In this study we show that efficient
tryptic digestion of proteins can be obtained in
seconds, simply by passing the sample through a
self-prepared column of POROS immobilized
trypsin material [9]. Preparation of the column
is quick and simple, and the required column
bed volume is typically less than 0.5 ~1. All
materials used are disposables, which eliminates
the risk of memory effects from previous runs.
The sample is passed over the column and eluted
directly onto the MALDI target in a single step,
which minimizes sample losses due to adsorption
to surfaces. Immobilization of the protease significantly
reduces autoproteolysis [8]. This
allows for an effective protease concentration,
many times higher than in solution.
2. Materials
N-octylglycopyranoside and modified trypsin
were obtained from Boehringer Mannheim
(Germany). Ammonium bicarbonate, iodoacetamide,
a-cyano-4-hydroxycinnamic acid, urea
and bovine serum albumin were purchased