Looking for recommendations for a protease inhibitor cocktail that is available locally in Xi'an with next-day delivery.

For liver protein extraction, it is recommended to directly contact a local Xi'an agent with a warehouse, rather than only checking brand official websites. When inquiring, do not just ask "Do you have cocktail?" You need to clarify two points: First, whether it is a 100× ready-to-use type, and the formulation should preferably include AEBSF, aprotinin, leupeptin, and pepstatin A. If phosphorylation detection will be performed subsequently, choose one that does not contain EDTA. Second, ask the other party to provide real-time inventory of the Xi'an warehouse and cold-chain delivery records, and confirm that it can be delivered to Yanta by the next morning. In terms of price, within 300 per vial, buying the 1 mL specification of a mainstream brand at 100× is usually sufficient, but after opening a single vial, it must be aliquoted and stored at -20 °C to avoid a decrease in potency caused by repeated use for 40-60 samples.

For this batch of 40–60 liver tissue samples, if calculated at 0.3–0.5 mL RIPA lysis buffer per sample, the total lysis buffer volume is approximately 12–30 mL. One 1 mL vial of 100× cocktail can prepare 100 mL lysis buffer, so a single vial can actually be used for two to three batches, but repeated freeze-thaw cycles after opening are the main cause of titer reduction. It is recommended to prioritize locally available stock in small packaging or pre-aliquoted formats, such as 100 μL/vial or 50 μL/tube, where one vial is sufficient for one batch, avoiding waste. Liver tissue has high cathepsin activity; prepare and use the cocktail fresh before homogenization, and the cocktail concentration in the lysis buffer can be added at the upper limit specified in the instructions, combined with low-temperature operation. If the commonly used formulation does not contain PMSF, PMSF must be prepared separately and cannot be added in advance.

It is recommended to first ask the local supplier to send the COA and expiration date screenshot, and not to accept only a verbal promise of "in stock." After arrival, perform a small-sample preliminary test: take the same liver tissue and divide it into two portions, lyse them with the old cocktail and the new cocktail respectively, and run Western blot to see whether the target protein and internal control are consistent, with particular attention to confirming that high-abundance proteins show no tailing and low-abundance proteins show no additional degradation. For supplier comparison, prioritize asking local Xi'an suppliers that have their own cold storage and support same-city flash delivery in Yanta, then check whether they provide trial packs or small samples, and whether they can issue VAT invoices and offer monthly settlement. Within a budget of 300 per unit, you can require delivery by "cold chain box + ice packs + thermometer," and inspect for signs of thawing upon arrival.