Purification and Characterization of an Antioxidant Protein from Pearl Oyster (Pinctada fucata martensii)

Protein from pearl oyster (Pinctada fucata martensii) was purified and characterized. Results showed that the pearl muscle protein (PMP) was composed of a single polypeptide with a molecular weight of approximate 11.6 kDa and contained 95.1% of the protein and 4.92% of the carbohydrate of the oyster. The polypeptide appears to be a glycoprotein, since the Fourier transform infrared (FTIR) spectroscopy of the PMP shows the typical characteristics of protein and polysaccharides. The denaturation temperature of the PMP was 81.3°C by differential scanning calorimetry. Circular dichroism spectroscopy showed that the PMP has a highly ordered structure. The PMP (200 μg/mL) showed a high oxygen radical absorbance activity (ORAC) of 6.57 μmol Trolox/μmol protein. Its antioxidant activity was stable at temperatures from 30–80°C and pH 2–10. The antioxidant activity was significantly inhibited by Zn2+, Ca2+, and EDTA and enhanced by Mn2+. The results suggest that the PMP could be used as a potential natural antioxidant.