Tyrosine phosphate is a frequently observed modification in a limited number of protein molecules, principally the products of viral oncogenes and membrane receptors for mitogenic growth factors. Such a group is therefore an attractive candidate for affinity selection of such phosphoproteins by antibodies with specificity for tyrosine phosphate. This report demonstrates that antisera raised against 4-aminobenzylphosphonic acid have specificity for tyrosine phosphate, but are not inhibited by tyrosine sulphate. This observation has important ramifications for the detection and isolation of phosphotyrosine-containing proteins without co-purification or detection of tyrosine sulphate-containing proteins, which are present in cells of all lineages. Furthermore, we demonstrate that antisera raised against the sulphanilate moiety are not reactive with tyrosine sulphate.

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