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| - Myoglobin Species with Enhanced Prooxidative Activity IsFormed during Mild Proteolysis by Pepsin
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| - Pepsin proteolysis at pH ∼4 resulted in a lowering of the (pseudo)peroxidase activity of metmyoglobinboth at physiological pH and at meat pH, as measured by a peroxidase assay with H2O2 and ABTSas substrates. In contrast, the mildly proteolyzed myoglobin had a strongly enhanced prooxidativeeffect on lipid oxidation in an oil in water methyl linoleate emulsion compared to native metmyoglobin,as evidenced by rates of oxygen depletion. More severe proteolysis of metmyoglobin at lower pHvalues near the optimum for pepsin did not result in a similar enhancement of prooxidative activity.The mildly proteolyzed metmyoglobin had spectral characteristics in agreement with a relativestabilization of the iron(II) state. On the basis of the observed effects of metal chelators, of lipophilicand hydrophilic peroxides and of radical scavengers on oxygen depletion rates, it is suggested thatthe increased prooxidative effect is due to radicals formed by cleavage of lipid peroxides by iron(II)/iron(III) cycling of a heme pigment with affinity for the lipid/water interface. Keywords: Lipid oxidation; myoglobin catalysis; proteolysis
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