Abstract
The complex between ferredoxin-NADP+ oxidoreductase and its proposed membrane-binding protein (Vallejos, R. H., Ceccarelli, E., and Chan, R. (1984) J. Biol. Chem. 259, 8048-8051) was isolated from spinach thylakoids and compared with isolated cytochrome b/f complex containing associated ferredoxin NADP+ oxidoreductase (Clark, R. D., and Hind, G. (1983) J. Biol. Chem. 258, 10348-10354). There was no immunological cross-reactivity between the 17.5-kDa binding protein and an antiserum raised against the 17-kDa polypeptide of the cytochrome complex. Association of ferredoxin-NADP+ oxidoreductase with the binding protein or with the thylakoid membrane gave an allotopic shift in the pH profile of diaphorase activity, as compared to the free enzyme. This effect was not seen in enzyme associated with the cytochrome b/f complex. Identification of the 17.5-kDa binding protein as the 17-kDa component of the cytochrome b/f complex is ruled out by these results.
Highlights
Identity between these polypeptides and their candidacy as the membrane-binding site for the reductase in vivo is examined by affinity chromatography and by immunological and enzymological approaches
Ferredoxin-NADP+ oxidoreductase was isolated from spinach thyductaseand its proposedmembrane-bindingprotein lakoids by affinity chromatography on Cibacron Blue [10]
Association of ferredoxin-NADPo’ xidoreductase with the binding protein or with the thylakoid membrane gave an allotopicshift in the pH profile of diaphorase activity, as compared to the free enzyme
Summary
Vol 260, No 28, Issue of December 5 , pp. 14891-14893,1985 Printed in U.S.A. The Ferredoxin-NADP+ Oxidoreductase-binding Protein Is Not the 17-kDa Component of the Cytochrome b / fComplex*. Hind [7] isolated a cytochrome b/f complex containing an additional 3’i”kDa polypeptide that was subsequently identified as ferredoxin-NADP’ oxidoreductase [8].Since the cytochrome b/f complex contains a-17-kDa subunit [9], it seemed possible thatthis subunit could be the 17.5-kDa binding protein of Vallejos et al [6]. Identity between these polypeptides and their candidacy as the membrane-binding site for the reductase in vivo is examined by affinity chromatography and by immunological and enzymological approaches
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