Preparation of BSA for X-ray scattering measurements
Bovine serum albumin (BSA) is a standard that is measured at least once before measuring your samples. The buffer for the BSA (50mM HEPES pH 7.5) and the BSA powder are in the fridge at the beamline.
- Weigh 5 mg of BSA in an eppendorf tube and add 1 ml of buffer.
- Mix by pipetting (try to do it calmly to minimize foam formation).
- Centrifugate for 10 minutes at maximum speed. To centrifugate at 4°C, there is a centrifuge in the User Lab.
- Put the supernatant in a fresh tube (it is quite possible that no pellet can be seen, but, to be safe, avoid touching with the tip the bottom of the tube while transferring to the new eppendorf).
- Measure the concentration of the solution at the NanoDrop spectrophotometer at the beamline. You can select BSA in the NanoDrop software to automatically calculate the concentration or in case you want to do it manually the extinction coefficient of BSA is 0.614 (Abs of 1 mg/ml). Usually, you should expect concentrations between 4 and 5 mg/ml.
- Before the measurement, add DTT to a final concentration of 2mM (1M stock aliquots can be found in the -20°C drawer you can also use them for your samples).