GFP Purified Protein

What it means: Fluorescence gives the excitation and emission maxima of the protein — excited near 488 nm and emitting near 509 nm, the standard enhanced GFP profile.

Why it matters:

• 488 nm is the argon-ion laser line present on essentially every flow cytometer and confocal microscope, so no special optics are needed.
• Knowing both maxima lets you confirm the filter set before running a standard curve — a mismatched emission filter simply loses signal.
• The Stokes shift is small, so excitation and emission bands must be well separated by the filter set to avoid bleed-through.

How to interpret here: Use the standard FITC/GFP channel. As a fluorometry standard, this protein reports what your instrument sees for a known quantity of GFP.

Tip: GFP fluorescence is pH sensitive — keep standards and samples in the same buffer when building a calibration curve.

What it means: Physical Format describes how the protein ships. Lyophilized means it is supplied freeze-dried and must be reconstituted before use, rather than arriving as a ready-to-pipette solution.

Why it matters:

• A lyophilized protein is far more stable in transit and storage than a frozen solution, which is why it carries a longer guaranteed life.
• Reconstitution volume is your choice, so the working concentration can be set to suit a standard curve rather than being fixed at the vendor's.
• Once reconstituted the stability clock changes completely — weeks, not a year.

How to interpret here: Centrifuge the vial briefly before opening so no powder is lost to the cap, then reconstitute to a concentration convenient for your assay and record it.

Tip: Reconstitute in the same buffer used for your samples — GFP fluorescence shifts with pH, so a mismatched diluent skews the standard curve.

What it means: Stability is how long the protein holds its stated performance. The lyophilized material is stable for at least one year from date of receipt at −20°C.

Why it matters:

• The clock starts at receipt rather than shipping, so the date on your own delivery note is the one that counts.
• Reconstituted protein is a different matter entirely — working aliquots keep for about one week at 2–8°C.
• A degraded standard fails quietly: the curve simply reads low, and the error propagates into every sample quantified against it.

How to interpret here: Keep the unopened vial lyophilized at −20°C until needed. After reconstitution, split into working aliquots and avoid repeated freeze/thaw cycles.

Tip: Reconstitute only what a run needs — a year of lyophilized life is worth more than a convenient stock solution.

What it means: Purity is the proportion of the preparation that is the intended protein. At greater than 90%, the remaining fraction is host protein and process residue carried through the affinity purification.

Why it matters:

• When the protein is used as a quantitative standard, purity sets the accuracy ceiling — a stated mass is only as meaningful as the fraction that is actually GFP.
• On an SDS gel or Western blot, contaminating bands from a lower-purity preparation can be mistaken for degradation products of the target.
• Purity above 90% is adequate for control and standard-curve use; it is not the same as the homogeneity a structural study would require.

How to interpret here: Treat the stated 50 µg as the total protein mass, of which more than 90% is GFP, and factor that into any calculation where absolute quantity matters.

Tip: Run one lane of the reconstituted standard alone on a gel the first time — it establishes what the contaminating bands look like before they appear beside a real sample.