What is the working concentration of N-succinyl-(Ala)3-Nitroanilide when doing Elastase assay

[feng zeng]

Hi,

Do any people know what is the work concentration of
N-succinyl-(Ala)3-Nitroanilide when doing Elastase assay?
And what will be the colour when this substrate reacts with Elastase?

I use the concentration 4.4mM, and and 20ul to make finally 200ul mixture of
Elastase, Buffer and Substrate, and then measure the OD at 410nm
I did not see good result:(

Thank you all
Feng