Phage antibodies against an unstable hapten: oxygen sensitive reduced flavin.

It is difficult to raise antibodies against haptens and antigens that are unstable under the physiological conditions of the serum. Here we have used a phage antibody library to isolate antibody fragments against oxygen sensitive reduced flavin, by selection of the phage under anaerobic and reducing conditions at pH 5 and a pre-elution step with the oxidized flavin. The binding of the reduced hapten to one of the antibody fragments was characterised by time-resolved polarised fluorescence, and shown to be highly specific for the reduced flavin.