Purification and Characterization of Thioredoxin f from Pea Leaves

Thioredoxin f from pea leaves was purified to homogeneity and characterized. The purification steps involved ammonium sulfate fractionation, heat treatment, Sephadex G-75 and G-50 gel filtration, and hydroxyapatite and DEAE ion exchange chromatography. The monomeric molecular weight of purified pea thioredoxin f determined by SDS polyacrylamide gel electrophoresis was 12,000. The purified protein was active in the presence of reducing agents, such as dithiothreitol, at an alkaline pH (7.8~8.5). It was stable against heat such that more than 40% of its maximum activity remained after treatment at $90^{\circ}C$ for 10 min. Pea thioredoxin f was able to reduce insulin and was specific only to pea chloroplast fructose-1,6-bisphosphatase.