Effects of hemopexin on hemin and hemoglobin-mediated lipid oxidation in washed fish muscle

Hemopexin (Hx) was isolated from pig blood using hemin-agarose chromatography. The effect of addition of Hx on hemin and hemoglobin (Hb) mediated lipid oxidation in washed cod muscle was investigated during iced storage at pH 5.5. At a 1:1 ratio of Hx to hemin, lipid oxidation as measured by development of thiobarbituric acid reactive substances (TBARS) was not significantly inhibited (p = 0.12). This may be attributed to a lack of hemin binding by Hx due to influence of pH and hemin precipitation. At a 1:2 ratio of Hx to Hb on a heme basis, TBARS development was significantly inhibited (p < 0.01) but not prevented. Equimolar addition of bovine serum albumin (BSA) in place of Hx did not inhibit TBARS development (p = 0.43). Hemin release from porphyrin-containing Hx, i.e. holoHx, and ferric sperm whale myoglobin (Mb) was measured at 37 °C, pH 5.7. Hemin release rates of 0.27 h^?1 and 0.05 h^?1, were calculated for holoHx and Mb, respectively. While the hemin affinity of Hx was greater than published values for trout Hb, the relatively low value measured for Hx compared to Mb may be caused by a combination of low pH and the absence of NaCl in the assays.