1. Each molecule of biotin bound to avidin protected four tryptophan residues from oxidation by N-bromosuccinimide, regardless of the occupancy of neighbouring binding sites in the four-sub-unit avidin molecule. 2. The oxidation products from avidin molecules in which some of the sites were occupied were separated on columns of Sephadex G-100. In the absence of biotin, oxidized avidin broke down into sub-units, which partly aggregated. When some of the sites were occupied by biotin, the only detectable products were completely oxidized avidin (sub-units and large aggregates) and unoxidized avidin–biotin complex (tetramer). Since the biotin-containing sub-units were randomly distributed before oxidation took place, they must have dissociated from the molecules containing oxidized sub-units and then reassociated to form the tetrameric avidin–biotin complex. 3. This reassociation still occurred in 3·5m-guanidinium chloride, which prevents the reassociation of unoccupied sub-units. During their brief existence in this medium, the sub-units of avidin–biotin complex were protected from oxidation by N-bromo-succinimide to the same extent as was the tetrameric complex. 4. It is concluded that sub-units of avidin–biotin complex do not readily lose their biotin, even in 3·5m-guanidinium chloride, and that monomeric biotin–binding species are probably present in solutions of avidin sub-units at guanidinium chloride concentrations between 3·0m and 3·5m.
Research Article| November 01 1968
The effect of N-bromosuccinimide on the sub-unit structure of avidin and its complexes with biotin
N. M. Green;
Biochem J (1968) 110 (1): 59–66.
- Views Icon Views
- Share Icon Share
N. M. Green, M. E. Ross; The effect of N-bromosuccinimide on the sub-unit structure of avidin and its complexes with biotin. Biochem J 1 November 1968; 110 (1): 59–66. doi: https://doi.org/10.1042/bj1100059
Download citation file: