Hi Anniee Younus . Acetic acid is fine for lowering the pH and stopping protease activity.

Use PMSF or ethanol to inhibit protease reaction. PMSF at about 10 mM shall inhibit the activity of serine proteases.

Yes you may use acetic acid in the place of tricholoroacetic acid....if your purpose is just halting the reaction u may follow what prof. Shamsher has suggested above

That depends on the buffer used for measurement and the pH optimum of your protease. Definitely you will need to have concentrated acetic acid to achieve the effect.

In terms of ease of use Acetic Acid concentration will need to be higher and thus an issue with fuming, unless you perform the assay in a fume hood. The TCA molarity you would normally use does not have that issue and can be used on the benchtop. Typically after the TCA precipitates the reaction and you either filter or centrifuge to remove the precipitate teh TCA containing supernatant is neutralized with Sodium Carbonate before Folin- Ciocalteau reagent is added. So before you would switch to acetic acid you need to run side by side experiments to see what effect the Acetic acid has on the Folin-Ciocalteau addition as well.

Residual protease activity can also be inhibited by addition of compounds that act as chelating, denaturing and antagonizing agents. You can even try SDS, EDTA and ethanol. Acetic acid produced noxious vapours!

The TCA, has a double role. 1. To acidify the reaction 2. Precipitate protein, including sustrate (casein, azocasein, or hemoglobin) and enzyme.

So, you ca not replaced by acetic acid at the same concentration.

The protease protocol has a TCA step in order to precipitate large protein an peptides and leting free short amono acids and small peptides, to measure the protease activity at 280 nm.

Hector