A radioimmunoassay for 1-beta-D-arabinofuranosyluracil with reference to cross-reactivity of 1-beta-D-arabinofuranosylcytosine with an antibody.

Antibodies directed against 1-beta-D-arabinofuranosyluracil have been produced in rabbits by immunization with a conjugate of 1-(5-O-succinyl-beta-D-arabinofuranosyl)uracil with human serum albumin. Two of four antibodies so obtained showed high specificity for 1-beta-D-arabinofuranosyluracil and allowed the development of a sensitive and reliable radioimmunoassay for this substrate. On the other hand, one antibody had a high affinity for 1-beta-D-arabinofuranosylcytosine. The binding of 1-beta-D-arabinofuranosylcytosine to this antibody was practically constant between pH 5.2 and 9.0, whereas 1-beta-D-arabinofuranosyluracil binding was affected drastically by pH. The pH-binding profile for 1-beta-D-arabinofuranosylcytosine and 1-beta-D-arabinofuranosyluracil was reminiscent of the specificity of ara-C-specific antibodies, which we previously obtained after immunization of rabbits with 1-(5-O-succinyl-beta-D-arabinofuranosyl)cytosine as a hapten.