Study of the reactivity of heme-proteins is relevant for the redox processes in the biological system and in the digestion of food. Myoglobin (Mb) is the major iron-heme protein of mammalian skeletal muscle and has as main biological function to supply the mitochondrial demand of oxygen in the muscle. In meat the Mb is the main pigment responsible for the color of the product, however during its digestion it can be activated by peroxides to hypervalent species that promote oxidative stress in the digestive tract. The zinc ion (Zn II) presents as a structural and / or functional component of several metalloenzymes and metalloproteins, participating in many reactions of cellular metabolism and physiological processes. Thus, the structure and reactivity of Mb was investigated compared to zinc ions. Absorption spectroscopy data suggests a conformational change of the protein consequently, a distortion of the porphyrin ring. An intrinsic fluorescence emission intensity of tryptophan (Trp) is increased with increasing concentration of zincII ions. The emission is not shifted in the fluorescence spectrum, indicating, in this way, the chemical environment of the Trp will remain hydrophobic. According to the Circular Dichroism (CD) data, there is an increase in the absolute value of the ellipticity signal, suggesting conformational changes over time. The deconvolution of the CD spectra reveals a decrease of the α-helical secondary structure and increase of the β-sheet structure with random structure. Through the microcalorimetric isothermal titration (ITC) data was determined the interaction between Mb and the zinc ions, the enthalpy parameters (ΔH =-88,07 ± 0,50 kJ mol-1), entropic parameters (ΔS =-208,78 ± 0,30 J mol-1 K-1) and a Gibbs free energy variation (ΔG =-25,85 ± 0,50 kJ mol-1) at 298 K. It was also possible to determine the equilibrium constant at 298 K (KA = (3.22 ± 0.2) x 10 4 L mol-1) with stoichiometry = 1: 1. The reduction of the ferrilmioglobin (MbFeIV = O) by cysteine produces metamioglobin (MbFeIII) and sulfomioglobin (SulfMbFeII), in the absence and presence of zinc ions II, the second order rate constant for the formation of the SulfMbFeII species at 298 K was 1.39 ± 0.16 L mol-1 s-1 and k'2 ≈ 3.25 ± 0.18 L mol-1 s-1 respectively. Transient absorption spectroscopy studies showed that Mb has a higher affinity for the ligand (O2 and CO) with zincin II ions in the reaction medium. The perferrilMb species was generated by the irradiation (355 nm) of the ferrilMb species. The study of Zn-perferrilMb versus the CO indicates the formation of the CO2 resulting in a reduction by 2 electrons forming the metamioglobin species.

Lista de figuras VI Lista de tabelas IX Lista de abreviaturas X