Mn(V) porphyrins featuring an oxo ligand trans to a hydroxo group offer a unique opportunity to compare the hydrogen atom abstraction ability of a protonated vs. a non-protonated high-valent oxo metal species, providing insight into the issue of oxo ligand protonation in Fe-containing biologically high-valent centers. Such a comparison is performed here by means of density functional calculations (DFT) on the manganese complex alongside with its Fe-containing counterpart (Fe(V)-oxo-hydroxo heme), showing that, regardless of the metal and within the same complex, both the oxo and the hydroxo ligands are very much able to abstract a hydrogen atom from a hydrocarbon (activation energies under 25 kcal mol⁻¹).