Abstract
Ligands of the RNH~2~ type which are covalently bound to agarose, cellulose, or cross‐linked dextranes by the conventional cyanogen bromide method are slowly detached from their supports by solvolytic processes occurring above pH 5 in aqueous surroundings. At pH values between 5 and 10, the free ligands, RNH~2~, appear in solution. Above about pH 10, the carbamyl derivative of the ligand, RNHCONH~2~, is the main product. Dilute ammonia releases iminocarbamyl derivatives, RNHC(NH)NH~2~. The latter type of compound has also been observed in tris(hydroxymethyl)‐aminomethane buffers at pH 8 and 9. Possible reaction mechanisms have been formulated on the basis of the structures suggested by Axén & Ernback for activated and substituted polysaccharides. Ligands attached to polyacrylamide gels (A) through amide bonds to carboxyl groups of the carrier, RNHCO·A, are released at slower rates and invariably as the free, unsubstituted ligand molecules. The release reaction appear to be general and independent of the particular ligand structure. We therefore advise caution with all experiments that can be adversely influenced by the presence of free ligands (e.g. localization of hormone receptors on the cell surface). At pH5, sepharose‐bound 8‐(ϵ‐aminocaproyl‐β‐aminoethylthio)‐adenosine‐3′, 5′‐cyclo‐monophosphate removes cyclic 3′, 5′‐adenosine‐monophosphate‐binding proteins from their solutions, but the corresponding polyacrylamide derivative does not (pH 7).