Protein expression tells you, how much protein you have. Protein activity tells you, how active the protein is.

Imagine you have workers supposed to dig a ditch. How many workers you have = protein expression. The more workers, the more work they do per time.

But rather than letting them work with bare hands :), you can give them shovels. This would be some activator, for example some allosteric activator or phosphorylation of *some* enzymes.

Or you can let them work without boots and thus inhibit their activity, because who would like to work without boots, right? This would be analogy of inhibition.

Other aspects that affect enzyme activity are for example temperature and pH.

Thus, 10 workers will do more work than 5 workers at the same conditions (=protein expression), but the conditions will affect, how much they will actually do (=enzyme activity).

Yes, to determine SIRT1's activity, you need some activity assay. There is surely something published. You would need to have acetylated protein and peptide and measure either removal of the acetate from the protein/peptide or formation of the O-acetyl-ADP-ribose (product), or decrease of NAD+ in the reaction.

There seem to be several activity kits available:

https://duckduckgo.com/?q=SIRT1+activity+kit&t=h_&ia=web

Hello,

For there to be activity, the protein must first be present, and for the protein to be present, it must first be expressed. Therefore, the expression of a protein allows its production, ie the gene which codes for this present is expressed and gives an mRNA, which will subsequently give a protein. Then, if the conditions are optimal for this protein, it will have an activity that can be measured, for example in the case of enzymes, either by measuring the disappearance of a substrate, or by the formation of a product.

Hi Kriti,

there are fluorometric SIRT1 activity assay kits available from different companies (i.e. Abcam ab156065 or Merck CS1040) that might address your question better than a WB.

Best,

Murat