Speaking generally, since I have no experience with this enzyme, the answer to your question would be YES only under certain conditions. For example, if PPO is always converted to PO rapidly on the time scale of your experiment, then the amount of PO produced is equal to the amount of PPO produced because all the PPO is converted to PO. Another example would be if the proportion of PPO converted to PO is always the same, no matter the circumstances. Contrarily, if the rate or proportion of PPO conversion to PO varies depending on the circumstances, then the answer is NO.

I think, yes; if all the PPO is converted to PO. 

Thank you Dr. Adam B Shapiro for your time and detailed answer. How can we observe whether all PPO is converted into PO or not?

I am observing PPO gene expression in insect larvae in response of some stress using real-time PCR (qPCR). I did not found any PPO reference to defend my results but PO, that's why i am curious to explain my results wisely.

Thanks Dr. Khallaf Mohamed for kind guidance.

It appears that others have explored the quantitiation of prophenol oxidase and phenol oxidase. Here is one reference:

http://rd.springer.com/article/10.1051%2Fapido%2F2010046

The measurement will involve performing an enzyme assay.