Modification of the reactivity of spinach chloroplast thioredoxin f by site-directed mutagenesis

Spinach chloroplast thioredoxin f has a third cysteine residue which is sur face exposed and close to the active site disulfide. In addition its N-term inus is rather long compared to other thioredoxins. By site-directed mutage nesis the third cysteine has been replaced, the long N-terminal tail has be en removed and the properties of the modified proteins have been examined. Truncation of the N-terminus renders the protein more soluble and stable an d has little in influence on its catalytic capacities. Replacement of the e xposed third cysteine clearly impairs its capacity to interact and reduce t arget enzymes and shows that this cysteine can be involved in homo-dimer fo rmation. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.