Lidstrom:Measuring 13C Incorporation Into Protein - CO2 Project

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Cell Prep

• Grow 1.5 mL of OD₅₅₀ 0.8 - 1.5 (approximately 0.3 - 0.8 mg) of cell culture
• Centrifuge 5 min at 13,500 g, 4^oC
• Swirl 30-40 seconds in ethanol dry ice bath or liquid N2 (don't freeze sample with liquid N2)
• Discard supernatant
• Wash pellet with 0.9% 1 mL of sodium chloride at 4^oC, pellet for 5 min at 13,500 g, 4^oC
• Repeat last step.4^oC

Optional:

• store pellet at -40 to -80^oC

Hydrolysis of Amino Acids

All steps in this section should be done in the fume hood:

• Suspend cell pellets in 1 mL of 6N HCl
• Transfer resuspended cells into 2 mL tubes
• Seal tubes to prevent evaporation of HCl
• Bake the well-sealed 2 mL tubes for 12-24 hours in a heating block set to 105 - 110 (not hotter)^oC
  • Hotter temps will may destroy some amino acids
• Dry the hydrolysate at 95^oC with constant air flow (or N₂) gas flow in the fume hood until the sample is completely dry.
  • Use the "nitrogen tree"
• Bake the dried samples at 105^oC for another 10 minutes to ensure no moisture is left.

Derivitization of Amino Acids

• Add 100 uL nanopure water to reconstitute the dried sample
• Transfer into filter centrifuge tubes
• Centrifuge at 13,500 g for another 1 - 2 minutes to remove ash
• Transfer into clean GC-MS vial with insert, and repeat drying step with nitrogen tree as done above
• Add 20 uL of pyridine to the dried sample
  • The solvent may turn slightly brown
• Add another 20 uL of Trifluoromethanesulfonic acid tert-butyldimethylsilyl ester (TBDMS) and seal well