Purification and Characterization of Ferredoxin-Sulfite Reductase from Turnip (Brassica rapa) Leaves and Comparison of Properties with Ferredoxin-Sulfite Reductase from Turnip Roots

Abstract

Ferredoxin-sulfite reductase (Fd-SiR) [hydrogen-sulfide: ferredoxin oxidoreductase, EC 1.8.7.1] from turnip leaves (SiR-L) has been purified to homogeneity and its enzymatic properties compared with that from turnip roots (SiR-R). Each enzyme had a molecular mass of 64.5±0.5 kDa by SDS-PAGE and an isoelectric point of 5.15±0.05. Although each had a pH optimum around 7.8 with the same effects of inhibitors, SiR-L had higher heat stability at 60°C than SiR-R. Moreover, SiR-R had a lower K_m and a higher specificity constant (k_cat/K_m) for turnip leaf ferredoxin than SiR-L. The N-terminal amino acid sequence of SiR-L was different from that of SiR-R. The results of amino acid analysis and peptide mapping suggested that SiR-L and SiR-R have different primary structures.