A method and kit for simultaneous detection and/or determination of a plurality
of modified proteins in a sample. The method comprises: a) contacting the sample
under mild protein denaturation conditions with a plurality of first antibodies
capable of binding to a specific target protein, the first antibodies being immobilized
on solid support material, each first antibody being differentiable from others
by a differentiation parameter, whereby the first antibodies bind to respective
target proteins present in the sample; b) removing unbound materials from the locus
of the first antibodies; c) contacting the materials from step (b) with one or
more second antibodies, each of which is specific to a class or subclass of modified
proteins or with a plurality of second antibodies, each of which is specific to
a modified protein, so as to bind the second antibody or antibodies to modified
proteins in the sample; and d) detecting and/or determining a plurality of modified
proteins in the sample. The kit comprises a plurality of primary antibodies immobilized
on solid support material, one or more buffers for lysing and for washing cellular
material samples to be assayed, an assay buffer for conducting the assay, the buffer
containing a sulfate or sulfonate detergent, and one or more second antibodies
specific to the modified proteins.