PsiP and PsiL are the two enzymes behind blue bruising. A team in Jena, Germany, reported in 2020 that PsiP, a phosphatase, removes the phosphate from psilocybin to give psilocin, and that PsiL oxidizes psilocin’s 4-hydroxy group so the units couple into blue chains (Lenz et al., 2020).
The names follow the “Psi” labels used for the psilocybin-building enzymes PsiD, PsiK, PsiM and PsiH (Fricke et al., 2017). The two bruising enzymes run the pathway partly in reverse: one undoes the phosphate step, the other uses up the product.
Much is still a proposal. The enzyme sequences hint that the two are kept apart from psilocybin in an intact mushroom, and the authors suggest the phosphate acts as a protective group (Lenz et al., 2020). The enzymes were pinned down in one species, though genes like PsiL turned up in every psilocybin-making fungus whose genome was available. A 2021 follow-up revised which blue product forms first (Lenz et al., 2021). Why the fungus does this, perhaps for defence, is unresolved.
Sources
- Lenz et al., 2020, Angewandte Chemie: enzymatic bluing
- Lenz et al., 2021, Chemistry – A European Journal
- Fricke et al., 2017, Angewandte Chemie: psilocybin biosynthesis
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