Ferredoxin-thioredoxin Reductase: Purification and Substrate Requirements

In the recent years, three systems capable of promoting the light activation of enzymes in higher plant chloroplasts have been described (Anderson, 1979; Buchanan, 1980). These three systems namely ferredoxin-thioredoxin, ferralterin and L.E.M. differ in their respective requirements toward the soluble proteins ferredoxin and thioredoxin, and also in their dependence on specialized molecules (L.E.M.) present on the thylakoid membranes. Accordingly, De La Torre et al. (1982) have isolated a soluble protein, ferralterin which is functionnaly independent of ferredoxin and thioredoxin. This protein exhibits spectral and subunit composition characteristics very similar to the ferredoxin-thioredoxin reductase purified by Schurmann (1981), the only difference between both proteins being the requirements toward Fd and Td. The soluble protein of the L.E.M. system, protein modulase, vas partially purified by Ashton/Anderson (1981); it shows functional characteristics identical to the ferralterin but so far nothing is known about its spectral and subunit composition.