Use of protein A-positive Staphylococci as adsorbent in a radioimmunoassay for cyclic AMP and cyclic GMP.

A reproducible (SD less than 4%), sensitive (in the 5 to 50 fmoles range) and inexpensive radioimmunoassay has been set up for the quantitation of cyclic. AMP and cyclic GMP based on acetylation or succinylation of the test sample. Separation of antibody-bound from free ligand was achieved by adsorption to formalinized protein A-positive Staphylococci of the Cowan 1 strain. The quantity of adsorbent (5% suspension) needed per 300 microliters of antiserum (diluted 24 x 10(4)) was 10 microliters. The blank value was below 2% and separation could be run at room temperature or at 4 degrees C as convenient. The acetylation or succinylation procedure of the sample totally eliminated interference of test sample immunoglobulins with antiserum binding to the absorbent.