[kyryx]

I am investigating potential cofactors of polyphenol oxidase (PPO or tyrosinase). For the experiment we used KCN and PTU to remove any potential Cu or Fe cofactors in PPO. Our results showed significant inhibition by both agents with catechol (1,2-dihydroxybenzene) as a reactant.

However, the part where I'm running into trouble is explaining the inhibition. All my lab manual shows is that catechol is oxidized to 1,2-benzoquinone, no mechanism. However, it doesn't seem like that is a very stable product. Also, the literature I was looking at was saying that the o-benzoquinone was just an intermediate. I couldn't seem to find a cohesive mechanism. The "water mechanism" from "Dawson  & Tarpley : The Catechol-Tyrosinase Reaction", seemed to make the most sense. Is there just no agreed upon mechanism? or am I missing something?

Also, I don't really understand the importance copper plays in this reaction. How does PPO use Cu? The answers I seem to be finding are just very general statements about how Cu of Fe stabilizes the molecule. I understand the question of enzyme cofactors is very broad, but if you could point me in the right direction I would really appreciate it.

Additionally, the other aspect I don't understand is why KCN and PTU had different levels of inhibition. Our lab manual just states that KCN has high affinity for Fe and Cu, while PTU only has affinity for Cu. It seemed to me that they would both exhibit similar affinity for cofactors. Also, our results showed that KCN was a better inhibitor. Is that because KCN just has a better affinity for Cu? I couldn't find any literature comparing their affinity for Cu.

[Babcock_Hall]

Frey and Hegeman "Enzymatic Reaction Mechanisms" has a very brief discussion of copper containing enzymes on pp. 241 and 242.  They give a proposed mechanism for galactose oxidase, which has a tyrosyl radical that is stabilized by copper.

[kyryx]

Frey and Hegeman "Enzymatic Reaction Mechanisms" has a very brief discussion of copper containing enzymes on pp. 241 and 242.  They give a proposed mechanism for galactose oxidase, which has a tyrosyl radical that is stabilized by copper.

I'll go check that out, thank you.