It has been shown previously that the thioredoxin system (thioredoxin + thioredoxin reductase + NADPH) may replace dithiothreitol (DTT) as a cofactor for vitamin KO and K reductase in salt-washed detergent-solubilized bovine liver microsomes. Here we demonstrate that the system can be improved further by adding protein disulphide-isomerase (PDI) to the components mentioned above. Moreover, NADPH may be replaced by reduced RNAase as a hydrogen donor. In our in vitro system the various protein cofactors were required at concentrations 2-5 orders of magnitude lower than that of DDT, whereas the maximal reaction rate was about 3-fold higher. PDI stimulated the thioredoxin-driven reaction about 10-fold, with an apparent Km value of 8 microM. These data suggest that in the vitro system the formation of disulphide bonds is somehow linked to the vitamin K-dependent carboxylation of glutamate residues. In vivo, both disulphide formation and vitamin K-dependent carboxylation are post-translational modifications taking place at the luminal side of the endoplasmic reticulum of mammalian secretory cells. The possibility that the reactions are also coupled in vivo is discussed.
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January 1992
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Research Article|
January 01 1992
Stimulation of the dithiol-dependent reductases in the vitamin K cycle by the thioredoxin system. Strong synergistic effects with protein disulphide-isomerase
B A M Soute;
B A M Soute
*Department of Biochemistry, University of Limburg, P.O. Box 616, 6200 MD Maastricht, The Netherlands
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M M C L Groenen-van Dooren;
M M C L Groenen-van Dooren
*Department of Biochemistry, University of Limburg, P.O. Box 616, 6200 MD Maastricht, The Netherlands
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A Holmgren;
A Holmgren
†Department of Physiological Chemistry, Karolinska Institute, P.O. Box 60400, S-10401 Stockholm, Sweden
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J Lundström;
J Lundström
†Department of Physiological Chemistry, Karolinska Institute, P.O. Box 60400, S-10401 Stockholm, Sweden
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C Vermeer
C Vermeer
*Department of Biochemistry, University of Limburg, P.O. Box 616, 6200 MD Maastricht, The Netherlands
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Publisher: Portland Press Ltd
Online ISSN: 1470-8728
Print ISSN: 0264-6021
© 1992 The Biochemical Society, London
1992
Biochem J (1992) 281 (1): 255–259.
Citation
B A M Soute, M M C L Groenen-van Dooren, A Holmgren, J Lundström, C Vermeer; Stimulation of the dithiol-dependent reductases in the vitamin K cycle by the thioredoxin system. Strong synergistic effects with protein disulphide-isomerase. Biochem J 1 January 1992; 281 (1): 255–259. doi: https://doi.org/10.1042/bj2810255
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