Volume 271, Number 24,
Issue of June 14, 1996
pp. 14240-14244
©1996 by The American Society for Biochemistry and Molecular Biology, Inc.
The FRE1 Ferric Reductase of Saccharomyces cerevisiae
Is a Cytochrome b Similar to That of NADPH Oxidase
(Received for publication, January 16, 1996, and in revised form, March 21, 1996)
Karolyn P.
Shatwell
,
Andrew
Dancis
¶
,
Andrew R.
Cross
,
Richard D.
Klausner
¶
and
Anthony W.
Segal
From the 
Department of Medicine, University College
London, 5 University Street, London WC1E 6JJ, United Kingdom,
¶ NICHD, National Institutes of Health, Bethesda, Maryland 20892, and 
Department of Molecular and Experimental Medicine, The
Scripps Research Institute, La Jolla, California 92037
Plasma membrane preparations from strains of the
yeast Saccharomyces cerevisiae gave a reduced minus
oxidized spectrum characteristic of a b-type cytochrome and
very similar to the spectrum of flavocytochrome
b558 of human neutrophils. The magnitude of the
signal correlated with the level of ferric reductase activity and the
copy number of the FRE1 gene, indicating that the FRE1
protein is a cytochrome b. Sequence similarities with the
flavin binding site of flavocytochrome b558 and
other members of the ferredoxin-NADP reductase family, together with
increased levels of noncovalently bound FAD and iodonitrotetrazolium
violet reductase activity in membranes from a yeast strain
overexpressing ferric reductase, suggested that the FRE1 protein may
also carry a flavin group. Potentiometric titrations indicated that
FRE1, like neutrophil NADPH oxidase, has an unusually low redox
potential, in the region of 
250 mV, and binds CO.
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