Purification and characterization of two ferredoxin-NADP+ oxidoreductase isoforms from the first foliage leaves of mung bean (Vigna radiata) seedlings

Abstract

Two forms of Fd-NADP+ oxidoreductase (FNR) isoproteins have been purified and characterized from the first foliage leaves of 5-d-old mung bean (Vigna radiata). They could be separated by either Mono Q HR 5/5 or ferredoxin (Fd)-Sepharose 4B affinity columns. Based on immunoblot analysis and N-terminal amino acid sequences, one form resembles the FNR purified from photosynthetic tissues of higher plants and the other resembles that from nonphotosynthetic tissues. Like their leaf and root FNR counterparts from spinach and radish, the mung bean leaf FNR isozymes differ from each other in primary structure and immunogenic properties but are similar in reaction activities, including cytochrome c reduction and NADP+ photoreduction assays. The mung bean isozymes also show similar kinetics parameters such as optimal pH and Km values for Fd and NADPH. Although the function of the root-type FNR in chloroplasts is not clear from in vitro experiments, we consider it plausible that it functions nonphotosynthetically, especially in seedlings at an early development stage. Two Fd isoforms were purified from young mung bean leaves, as reported on Fds in higher plant leaves. Based on their N-terminal sequences, both mung bean isoforms were similar to leguminous leaf Fds.