Thioredoxin and NADP-thioredoxin reductase from cultured carrot cells.
Dark-grown carrot (Daucus carota L.) tissue cultures were found to contain both protein components of the NADP/thioredoxin system--NADP-thioredoxin reductase and the thioredoxin characteristic of heterotrophic systems, thioredoxin h.  Thioredoxin h was purified to apparent homogeneity and, like typical bacterial counterparts, was a 12-kdalton (kDa) acidic protein capable of activating chloroplast NADP-malate dehydrogenase (EC 1.1.1.82) more effectively than fructose-1,6-bisphosphatase (EC 3.1.3.11).  NADP-thioredoxin reductase (EC 1.6.4.5) was partially purified and found to be an arsenite-sensitive enzyme composed of two 34-kDa subunits.  Carrot NADP-thioredoxin reductase resembled more closely its counterpart from bacteria rather than animal cells in acceptor (thioredoxin) specificity.  Upon greening of the cells, the content of NADP-thioredoxin-reductase activity, and, to a lesser extent, thioredoxin h decreased.  The results confirm the presence of a heterotrophic-type thioredoxin system in plant cells and raise the question of its physiological function.
Johnson
T C
TC
Division of Molecular Plant Biology, University of California, Berkeley 94720, USA.
Cao
R Q
RQ
Kung
J E
JE
Buchanan
B B
BB
D002478:Cells, Cultured; D002736:Chloroplasts / Q000201:enzymology; D018552:Daucus carota / Q000737:chemistry / Q000166:cytology* / Q000201:enzymology* / Q000648:ultrastructure; D008854:Microscopy, Electron; D013880:Thioredoxin-Disulfide Reductase / Q000032:analysis*; D013879:Thioredoxins / Q000032:analysis*
D013879:Thioredoxins; D013880:Thioredoxin-Disulfide Reductase