BPL catalyzed reaction: 10 mM Tris-HCl p H-7.5 containing 5 nM BPL, 3 mM ATP, 5.5 mM MgCl₂, 500 µM biotin but no BCCP were incubated at 37°C for 1 h. The reaction mixture was then loaded on to Superdex S 200. Peak 1: Dimeric BPL –bio 5′AMP-BPL (M_r ~60,000±2900 Da). Peak 2: Monomeric BPL (M_r ~29,500±150 Da). Peak 3: Unreacted ATP.