Hello every researcher

I'm performing gelatin zymography to test whether MMPs of the cell would increase or not under the drug treatment, I followed the protocol (attached file you can see the details) to do my gelatine zymography. After a wash step, I put the two gels in the incubation buffer for 24 and 48 hr. However, the 24 hr gel is more obvious than the 48 hr after destaining. Does someone ever meet this issue, or can some ideas be shared?

Thanks