Purification and characterization of metmyoglobin reductase from ordinary muscle of blue-fin tuna

Metmyoglobin (Met-Mb) reductase from blue-fin tuna ordinary muscle was puri fied to electrophoretical homogeneity by ammonium sulfate fractionation, io n exchange and organomercurial agarose affinity chromatography. The molecul ar weight estimated by SDS-PAGE was 100 kDa. The optimal pH and temperature for the reduction of met-Mb were 7.3 and 25 degrees C, respectively. This enzyme was very stable at pH 7.0-7.3 and 4 degrees C-15 degrees C. The puri fied enzyme was strongly activated by K+, moderately activated by Na+ and M n2(+), but not affected by Ni2+. It was moderately inhibited by Li+, NH4+, Mg2+, and Co2+. The Vmax for the reduction of met-Mb and NADH were 0.32 and 0.43 mMl/min/mg, while Km were 2.3 x 10(-5) and 24.4 x 10(-5) M, respectiv ely.