MIN
The
B. M
*The or
Atlan 5
Recei lish
Th
conv
zym
nent
Una
oxid
com
oxid
tivit
syste
crui
The
mem
pand
whic
Ke
p47
P
NA
neut
phag
oxid
O
2
2
i
rical
phag
NAD
plas
a bro
ot
e
rat
ne
se
ne
0),
en
e
di
se
wi
Finally, the reaction H
2
O
2
1 HOCl can produce singlet
oxygen (
1
O ) (14), a more energetic form of oxygen that
1
T
2
A
metal
342
Archives of Biochemistry and Biophysics
Vol. 3
doi:10 oDPH oxidase (1) is an enzyme that is located in
rophils (2), eosinophils (3), and mononuclear
ocytes (4) and catalyzes the generation of super-
e (O
2
2
)
2
from oxygen and NADPH (5):
NADPH 1 O
2
3 NADP
1
1 H
1
1 O
2
2
.
s converted to H
2
O
2
, which represents stoichiomet-
ly the bulk of oxygen consumed by stimulated
ocytes (6, 7). Concurrent with activation of the
2
can attack double bonds.
The phagocyte oxidase consists of four components
that are essential for activity: the heterodimeric mem-
brane-associated flavocytochrome b
588
protein, which is
composed of gp91
PHOX
(15) and p22
PHOX
(15); the cytoso-
lic components p47
PHOX
(16) and p67
PHOX
; and the small
GTPase(s) Rac 1 or Rac2 (17). An additional compo-
nent, p40
PHOX
, is also associated with the oxidase, but
its functional role is unclear (see below). The stability
of each subunit of flavocytochrome b558 depends onIREVIEW
Neutrophil NADPH Oxidase
. Babior,*
,1
J. D. Lambeth,† and W. Nauseef ‡
Scripps Research Institute, La Jolla, California 92037; †Em
ta, Georgia 30322; and ‡University of Iowa, Iowa City, Iowa
ved September 20, 2001, and in revised form October 12, 2001; pub
e NADPH oxidase of phagocytes catalyzes the
ersion of oxygen to O
2
2
. This multicomponent en-
e complex contains five essential protein compo-
s, two in the membrane and three in the cytosol.
ssembled and inactive in resting phagocytes, the
ase becomes active after translocation of cytosolic
ponents to the membrane to assemble a functional
ase. Multiple factors regulate its assembly and ac-
y, thus serving to maintain this highly reactive
m under spatial and temporal control until re-
ted for antimicrobial or proinflammatory events.
recent identification of homologs of one of the
brane components in nonphagocytic cells will ex-
understanding of the biological contexts in
h this system may function. © 2002 Elsevier Science
y Words: NADPH oxidase; cytochrome b
558
; p67
PHOX
;
HOX
.
pr
Th
st
in
da
ge
(1
ag
ar
ad
da
lo
97, No. 2, January 15, pp. 342–344, 2002
.1006/abbi.2001.2642, available online at http://www.idealibrary.comPH oxidase, intracellular granules fuse with the
ma membrane or phagosomal membrane to release
ad array of biologically active molecules, including
hete
gp91
unit
two
bran
for b
W
comp
o whom correspondence should be addressed.
bbreviations used: MPO, myeloperoxidase; O
2
2
, superoxide; M,
.y University Medical School,
2246
ed online December 19, 2002
eases, antimicrobial proteins, and peroxidases.
H
2
O
2
generated by the oxidase serves as a cosub-
e for peroxidases, either myeloperoxidase (MPO)
utrophils and monocytes (8) or eosinophil peroxi-
in eosinophils (9), in the oxidation of halides to
rate hypohalous acids. In the case of neutrophils
the HOCl produced is a potent antimicrobial
t that in turn spawns long-lived chloramines that
in themselves cytotoxic (reviewed in Ref. 11). In
tion to these reactive products, the NADPH oxi-
also generates hydroxyl radical, made by the fol-
ng metal (M)-catalyzed reaction (12, 13):
H
2
O
2
1 M
1
3 OH z 1 OH
2
1 M
21
M
21
3 M
1
.
nrodimer formation (18), so mutations in either
PHOX
or p22
PHOX
result in the absence of both sub-
s from the cell surface. Flavocytochrome b558 has
heme groups, each buried in or near the mem-
e, and sequences consistent with binding motifs
inding flavin (19) and for NADPH.
hen considering potential roles of the individual
onents of the NADPH oxidase during stimulation
0003-9861/02 $35.00
© 2002 Elsevier Science
All rights reserved.

of ph
expo
Whe
the N
comp
to se
the a
face
oxid
resu
othe
a PX
actio
tran
the p
on p
alan
does
equi
sible
C (2
form
prot
but
p22
P
activ
thes
tide
curs
initi
P4
whic
ing a
The
;13
main
prot
p47
P
spec
part
phag
cont
main
thou
NAD
tion
for a
chro
hydr
part
p67
P
flavo
func
p67
P
to r
chro
g t
e
ed
5,
nc
r i
id
tos
o
7
P
Su
ect
an
91
ed
iri
m
g p
nt
in
np
nc
R
is
ons
ou
m
ing
an
se
FE
. P
2
. B
(1
. B
P
. B
J
. B
In
. R
a
. M
es
. F
is
. H
J
. A
N
. H
B
. K
DPagocytes, it is convenient to recognize that agonist
sure triggers both its assembly and activation.
reas gp91
PHOX
serves as the electron transporter of
ADPH oxidase (20), the functions of the cytosolic
onents are less precisely defined. p47
PHOX
appears
rve as an adaptor protein, providing a platform for
ssembly of a functional enzyme at the cytoplasmic
of cytochrome b
558
. Serving as a switch to trigger
ase assembly, phosphorylation of p47
PHOX
(21, 22)
lts in a conformational rearrangement, exposing
rwise cryptic SH3 motifs, proline-rich regions, and
domain (see below) that together mediate inter-
ns both with cytochrome b
558
and p67
PHOX
. P47
PHOX
slocation and oxidase activity appear to require
hosphorylation of one of a specific pair of serines
47
PHOX
: the conversion of S303 and S304 to the
ine equivalents eliminates oxidase activity (23), as
the conversion of S359 and S370 to the alanine
valents (24). The kinase that seems to be respon-
for most of the phosphorylation is protein kinase
5), although it is not known which specific iso-
(s) of protein kinase C is responsible. Another
ein kinase that also phosphorylates p47
PHOX
is Akt,
with weaker activity (unpublished). Like p47
PHOX
,
HOX
and p67
PHOX
are also phosphorylated upon cell
ation, although the functional significance of
e phosphorylations is uncertain. Guanine nucleo-
exchange of Rac–GDP to form Rac–GTP also oc-
, and this also appears to be an essential trigger for
ating oxidase assembly and activation.
7
PHOX
contains tandem SH3 (26) domains one of
h is bound to a remote polyproline domain, form-
fold that opens when the protein is activated (27).
amino terminus of p47
PHOX
contains also a region of
0 amino acids previously described as a PX do-
, being first recognized in the phagocyte oxidase
eins p40
PHOX
and p47
PHOX
(28). The PX domains of
HOX
and p40
PHOX
have been demonstrated to bind to
ific phosphoinositides and may thus mediate in
the assembly of the oxidase at the plasma or
osomal membrane (29–31). P67
PHOX
(26) likewise
ains two SH3 domains and a NADPH binding do-
of mysterious function. The function of p67
PHOX
is
ght to be to regulate the transfer electrons from
PH to flavin (32, 33). P67
PHOX
contains an “activa-
domain” (amino acids ;200–210) that is essential
ctivation of the electron flow within flavocyto-
me b558. This region is thought to regulate the
ide transfer from NADPH to FAD. Rac likewise
icipates in electron transfer and independently of
HOX
regulates transfer from NADPH to FAD by
cytochrome b
558
(34). According to one view, the
tions of both p47
PHOX
and Rac are to bind and orient
HOX
so as to arrange properly its activation domain
in
ar
ne
(3
fu
fo
ox
cy
am
p6
el
ch
gp
m
sp
do
in
ce
te
no
fu
in
th
ti
gr
ho
pl
tr
da
RE
1
2
3
4
5
6
7
8
9
10
11
12
THE NEUTROPHIL NAegulate the electron flow within the flavocyto-
me b558. This is consistent with recent data show-
(1
13. Lhat when high concentrations of p67
PHOX
and Rac
present in a cell-free system then p47
PHOX
is not
ed to reconstitute high NADPH oxidase activity
36). A fourth soluble component is p40
PHOX
, whose
tion is not clear, although there is evidence both
ts potentiating (37) and for its terminating (38)
ase activity. P47
PHOX
, p67
PHOX
, and p40
PHOX
form a
olic complex in which p47
PHOX
is about 1:1, but the
unt of p47
PHOX
is three to four times the quantity of
HOX
(39).
peroxide production by the NADPH oxidase is an
rogenic process (40) and is accompanied by proton
nel activity, attributed in several studies to
PHOX
(41–43). Although the capacity of gp91
PHOX
to
iate proton efflux is generally accepted, there is
ted controversy as to whether gp91
PHOX
is the pre-
inant voltage-gated proton channel activated dur-
hagocyte stimulation (44, 45). The relatively re-
appreciation that gp91
PHOX
is a member of a pro-
family whose members are expressed widely in
hagocytic cells and likely mediate a wide array of
tions unrelated to antimicrobial activity (reviewed
ef. 46) may provide important insights pertinent to
controversy. A splice variant of NOX1 (47) func-
as a proton channel despite the absence of heme
ps or oxidase activity. Ongoing studies of gp91
PHOX
ologs may provide important insights into the cou-
and functional significance of electron and proton
sport activities attributed to the phagocyte oxi-
.
RENCES
ark, J.-W., Scott, K. E., and Babior, B. M. (1999) Exp. Hematol.
6, 37–44.
atot, G., Martel, C., Capdeville, N., Wientjes, F., and Morel, F.
995) Eur. J. Biochem. 234, 208–215.
olscher, B. G. J. M., Koenderman, L., Tool, A. T. J., Stokman,
. M., and Roos, D. (1990) FEBS Lett. 268, 269–273.
rozna, J. P., Hauff, N. F., Phillips, W. A., and Johnston, R. B.,
r. (1988) J. Immunol. 141, 1642–1647.
abior, B. M., Kipnes, R. S., and Curnutte, J. T. (1973) J. Clin.
vest. 52, 741–744.
oos, D., Eckmann, C. M., Yazdanbakhsh, M., Hamers, M. N.,
nd de Boer, M. (1984) J. Biol. Chem. 259, 1770–1775.
akino, R., Tanaka, T., Iizuka, T., Ishimura, Y., and Kanag-
aki, S. (1986) J. Biol. Chem. 261, 11444–11447.
urtmuller, P. G., Burner, U., and Obinger, C. (1998) Biochem-
try 37, 17923–17930.
orton, M. A., Larson, K. A., Lee, J. J., and Lee, N. A. (1996)
. Leukocyte Biol. 60, 285–294.
lbrich, J. M., McCarthy, C. A., and Hurst, J. K. (1981) Proc.
atl. Acad. Sci. USA 78, 210–214.
ampton, M. B., Kettle, A. J., and Winterbourn, C. C. (1998)
lood 92, 3007–3017.
adiiska, M. B., Burkitt, M. J., Xiang, Q.-H., and Mason, R. P.
343H OXIDASE995) J. Clin. Invest. 96, 1653–1657.
iochev, S. I. (1996) Free Radical. Res. 25, 369–384.