Effect of biotinylation on the thermal stability of streptavidin. Streptavidin, at a concentration of 10 μM, was incubated with biotin at biotin : streptavidin molar ratios of 0 : 1, 0.25 : 1, 0.5 : 1, 1 : 1 or 2 : 1 for 30 min at either 22°C (A) or 100°C (B). Samples were analysed by SDS-polyacrylamide gel electrophoresis, and proteins were visualized by staining with Coomassie brilliant blue. The positions of molecular mass markers (kDa) are shown on the right.