It is important to note that using ESI it was not possible to isolate the mass peak M + . In the MS spectra of H-Tyra, a species with m/z 926.3 was detected with a high intensity, which, following isolation and fragmentation, yielded a new species at m/z 890.86 with a mass loss of 36 (Fig. ). This suggests that the parent species is hemin/tyramine-tetra-aqua conjugate [C50H58FeN6O8] + , containing two water molecules bound to the amide bonds, while the other two molecules are bound to Fe(III). This ion yields hemin/tyramine-bis aqua conjugate [C50H54FeN6O6] + . The latter species was fragmented further with a loss of molecules (total m/z 71). Moreover, the main molecular ion species [C50H50FeN6O4] + (m/z 854.2) yielded fragments with different MW following the degradation of different peripheral groups. This was mainly at the conjugated position to tyramine (fig. ). This finally generated an intact tetrapyrrolic macrocycle [C30H28FeN4] + (m/z 499.1) attached to the peripheral -CH3 and -CH=CH2 groups only.