We noted while “pinning metabolites” that allantoin was present in the mass spec data from UCSD. This metabolite is not supposed to be present in humans; it is a breakdown product of purines in some animals, but in humans and other primates, the producing enzyme does not exist, and instead, uric acid (urate) is the final product of purine catabolism. Or at least so I thought.

It turns out that urate can spontaneously oxidize to form allantoin, and some think that this is an indicator of oxidative stress (whatever that means in this context). But there are also concerns that this is an artefact of sample handling conditions. It would be interesting to see if cells with labeled purines produce labeled allantoin …