I love this stuff, thanks for the reply. With PQQ, we see it occurs only in tiny amounts in nature, but is there nevertheless. This suggests its role as a catalyst, and I'd expect it to behave differently if taken in large amounts. For example, Dr. Koch wrote he could effect recoveries using benzoquinone when diluted to 10(-9) or 10(-12), but that at 10(-5), it actually caused some serious problems. So when I see a PQQ supplement containing 20 mg, I scoff at it. 300 mcg might be more appropriate. Wagner, Kreher and Jurcic showed this very nicely in a graphic in Arzneimittel-Forschung 38(1):273-275
I wouldn't just go throwing all sorts of quinones at something, I'd think to be selective and especially about amount. We see the K series of vitamins being quinones. Also ubiquinone which is Co-Q10. A good book is "Naturally Occuring Quinones" by R. Thomson.
Indeed, the metals are important, one example is manganous ion, necessary for arginase function. Arginase hydrolyzes arginine to ornithine and urea. Arginine itself is essential for the growth of malignant tumors, mammals don't synthesize it, it comes from diet. It is 2X as abundant in malignant vs. normal cells. It is the guanidine portion which the cancer cells need. Avoiding arginine in foods and ensuring adequate Mn seems like a good idea as general dietary practice. Interestingly, Arginase II is located in mitochondria.