I want to use lipase to carry out a function, but then be switched off before the next phase, which is toxicity testing. I don't want the lipase affect the next phase, and I can't heat it.
There are several types of lipases (not all share the same structure, capabilities nor pH sensitivities etc. ). pH will deactivate all enzymes but it depends on how low the pH needs to be which may affect other components in your toxicity sample even if you bring back the pH to what the sample was before lowering its pH. Enzymes are short lived and their activity can be just a few hours. I think you may want to do the following test:
Switch off the enzyme temporarily and collect a sample. Take the pH at least 2 pH units below the lower range of the optimum pH for your lipase in question. Stir the low pH sample for a couple of hours. Bring back pH of sample to pH 7 and filter with bacteria filter (0.2 micron syringe filter) ....apply on Spirit Blue agar to see if you get a lipase reaction. Conduct a control test (sample with no pH modification) for comparison.
pH a crucial for the activity of any enzyme it may be. As lipase obtained from different sources will differ in characteristics, it will have different pH optima for the best activity in each case. You can find more on this via the following link.
https://pubmed.ncbi.nlm.nih.gov/3234304/
For your case, if you want to inactivate your lipase for the next phase using pH firstly you will have to optimize the pH optima for your enzyme activity. For instance, if lipase shows activity at pH range 4-8 (with highest say at 6) and is inactive below 4 and above 8, then you can get your medium to as low as 3 (at least) or over 8 (9 or 10 maybe) to keep your lipase inactive at your will.
just make sure that the change in pH to this level is not affecting the other conditions of the test in progress.
This is not possible because the enzymes are sensitive to the change in pH
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