None if your protein used as standard is different from the one you want to quantify. If they are the same protein, then use the simplest

Hi Hossain, both of these assays are outdated and haven't been used for awhile..

But if this is the only assays available to you, I would recommend precipitation by 1% TCA and measure the supernatant at 280 nm compared to TCA precipitation of the original substrate before the proteinase treatment to get a baseline. 

Thanks Dr. Omar Gonzalez-Ortega! Sorry I didn't explain well. Its to measure activity of secreted protease in a culture supernatant using casein as substrate.

Thanks Dr. Steingrimur Stefansson! Could you recommend other protocol please? The purpose is to determine protease activity in culture-supernatant using casein as the substrate

Hi Hossein, you are limited by the job you have to do.

If the protocol calls for estimating the hydrolysis of casein, then you have to follow it.

Any changes in the protocol will have to be followed by control experiments, comparison and optimization.

The golden rule of assays is that if they work, don't mess with them

Thanks again Dr. Stefansson! I already purchased casein. Most articles I read have reported casein as the substrate for this kind of assay; some, however, used azocasein. But I may try other methods too, if better than this one.