Study On The Spectral Structure And Photostability Of Metmyoglobin In Pig’s Myocardium

China is the largest producer and consumer country of pork in the world.Pork quality is paid more and more attention,due to the increase of pork yeild.The dynamical balance of Mb-MbO2-MetMb will affect pork color which directly reflects the meat quality.Therefore,the new field of meat science is to explore the relationship between myoglobin molecular structure and function by functional proteomics.In this paper,the structure and photostability of metmyoglobin in pig’s myocardium(pMetMb)were studied by spectra and was classified by UV and MALDI=TOF/TOF.1 Senior structural features of pMetMbThere were 6 diffraction peaks and 93.6%±1.37%crystallinity of pMetMb by X-ray diffraction(XRD)so that it was belonged to the monoclinic crystal.Other results were also showed that pMetMb was a compound had a peptide chain,called as the main carbon skeleton,containing benzene,methyl amine,amide,hydroxyl,methyl and so on.In the centre of pMetMb,the porphyrin ring(heme-Fe3+)was made up of imidazole and Fe groups.The pMetMb secondary structures had four,as α-helix,β-sheet,β-turn and random in the far ultraviolet area by circular dichroism(far-UV CD)spectra.Because of 95.6%a-helix in its secondary structure,it was assigned to full a-helix style.In the near ultraviolet area,both of disulfide bond(-S-S-)and tryptophan residue(Trp-)at 250-320nm or 293nm were assigned to the special domains of protein-peptide chain.The structures and domains of pMetMb also were assigned to its belonging globin.When pMetMb identified by fluorescence,its mocular contained auto-fluorescent substances,in which were Tyr-,Trp-and heme-Fe3+ were at 312nm,355nm and 630nm,respectively.The fluorescence lifetime of aromatic amino acids was 2.89ns,while that of heme-Fe3+ was 0.32ns so that the former was longer than that of the latter(p<0.01).Therefore,pMetMb was assigned to six-coordinated low-spin(6-cLs)with fluorescence emission peak at 630nm and the UV absorbing peak at 409nm.2 The photostability of pMetMb under ultravioletAs we all known,UV is one of the strongest lights in nature.For this reason,UV was used to study the pMetMb photostability.The results were showed that domains of pMetMb were destroyed at first.It’s found that Tyr-was hurt and the secondary structure of a-helix was misfolded after 5 minutes exposed to UV.pMetMb continuously under UV long time,inn hydrophobic group-Trp-was out or surface.However,heme-Fe3+ was highly sensitive to UV.Its fluorescence intensity had been decreasing step by step with fluorescence quenching to 1/10(p<0.01).It might be identified that pMetMb was a UV sensitive protein.In summary,pMetMb tertiary structure and domains were destroyed initially.For these,electronic and energy-level transitions in domains were reduced.Furthermore,its secondary structure was depolymerized and hydrophobic group(Tyr-)was denaturation.As pMetMb lost its redox,meat was fade.