This procedure may be used for determination of Pepsin activity using hemoglobin as the substrate. It is a spectrophotometric stop rate determination.
Unit Definition: One unit of Pepsin will produce a ΔA280 of 0.001 per minute at pH 2.0 at 37 °C measured as trichloroacetic acid (TCA)-soluble products using hemoglobin as the substrate. (Final volume = 16 ml, light path = 1 cm.)
1.0 M Hydrochloric Acid
Please consult the Safety Data Sheet for information regarding hazards and safe handling practices.
Use ultrapure water (≥18 MΩxcm resistivity at 25 °C) for the preparation of reagents.
10 mM HCl (Hydrochloric Acid) – Dilute 1.0 M Hydrochloric Acid 100‑fold with ultrapure water.
2.5% (w/v) Hemoglobin Stock Solution – Prepare a 25 mg/ml solution in ultrapure water using Hemoglobin from bovine blood (Catalog Number H2625). Stir vigorously, creating a vortex, for a minimum of 10 minutes at 37 °C. Then filter through a polypropylene column with a coarse filter (90–130 mm).
Substrate [2.0% (w/v) Hemoglobin solution] – Transfer 80 ml of the filtered 2.5% (w/v) Hemoglobin Stock Solution into a suitable container. Adjust the pH of this solution to 2.0 at 37 °C using 5 M HCl. Bring the final volume to 100 ml with ultrapure water.
Enzyme Solution (Pepsin) – Prepare a 1 mg/mL stock solution in cold (2–8 °C) 10 mM HCl. If insoluble material is present, allow the stock solution to sit on ice until dissolved. When the Pepsin has dissolved or, if insoluble material is still present, after 1 hour, dilute the 1 mg/mL stock solution further to 0.01–0.05 mg/ml Enzyme Solution in cold 10 mM HCl.
1. Pipette the Substrate into suitable glass vials.
2. Place vials in a thermostatted water bath and equilibrate to 37 °C for ~10 minutes, then add:
3. Mix by swirling and incubate at 37 °C for exactly 10 minutes, then add:
4. Mix by swirling and incubate at 37 °C for an additional 5 minutes.
5. Filter the Blank and Test mixtures through a 0.45 µm syringe filter. Using a spectrophotometer, record the A280 versus air for each filtered solution for each vial.
|Units/ml enzyme =||
df = Dilution factor
10 = Assay incubation time in minutes
1.0 = Volume of Enzyme Solution (ml) added
0.001 = ΔA280 per unit of Pepsin (unit definition)