Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:1.6.99.6 (NADPH oxidase)
 10,295 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The superoxide-generating NADPH oxidase system in phagocytes consists of at least membrane-associated cytochrome b558 and three cytosolic components named SOCI/NCF-3/sigma 1/C1, SOCII/NCF-1/p47-phox, and SO-CIII/NCF-2/p67-phox. p47-phox and p67-phox were isolated, and their primary structures were determined, but SOCI has not been well characterized. In the present study, we first purified SOCI to homogeneity from the cytosol fraction of the differentiated HL-60 cells. The purified SOCI was a small GTP-binding protein (G protein) with a M(r) of about 22,000. The guanosine 5'-(3-O-thio)triphosphate-bound form, but not the GDP-bound form, of this small G protein showed the SOCI activity. The partial amino acid sequence of SOCI thus far determined was identical to the amino acid sequence deduced from the cDNA encoding rac2 p21. None of the purified small G proteins, including Ki-ras p21, smg p21B/rap1B p21, rhoA p21, and rac1 p21, showed the SOCI activity. These results indicate that SOCI is a small G protein very similar, if not identical, to rac2 p21. The GDP/GTP exchange reaction of SOCI was stimulated and inhibited by stimulatory and inhibitory GDP/GTP exchange proteins for small G proteins, named smg GDS and rho GDI, respectively. The NADPH oxidase activity was also stimulated and inhibited by smg GDS and rho GDI, respectively. These results indicate that the superoxide-generating NADPH oxidase system is regulated by both smg GDS and rho GDI through rac2 p21 or the rac2-related small G protein in phagocytes.
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PMID:Regulation of the superoxide-generating NADPH oxidase by a small GTP-binding protein and its stimulatory and inhibitory GDP/GTP exchange proteins. 131 93

rac1 and rac2 p21s are ras p21-like small GTP-binding proteins which are implicated in the NADPH oxidase-catalyzed superoxide generation in phagocytes. rac1 and rac2 p21s have a Cys-A-A-Leu (A = aliphatic amino acid) structure in their C-terminal region which may undergo post-translational processing including prenylation, proteolysis, and carboxyl methylation. We studied the function of this post-translational processing of rac p21s in their interaction with the stimulatory and inhibitory GDP/GTP exchange proteins for rac p21s, named smg GDS and rho GDI, and in their NADPH oxidase activation. We produced human recombinant rac1 and rac2 p21s in insect cells and purified them from the membrane and soluble fractions as the post-translationally processed and unprocessed forms, respectively. Post-translationally processed rac1 and rac2 p21s were sensitive to both smg GDS and rho GDI, but post-translationally unprocessed rac1 and rac2 p21s were insensitive to them. The GTP gamma S (guanosine 5'-(3-O-thio)triphosphate)-bound form of post-translationally processed rac1 and rac2 p21s stimulated the NADPH oxidase activity, but post-translationally unprocessed rac1 and rac2 p21s were far less effective. These results indicate that both rac1 and rac2 p21s stimulate the NADPH oxidase activity and that their post-translational processing is important not only for their interaction with smg GDS and rho GDI but also for their NADPH oxidase activation.
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PMID:Post-translational processing of rac p21s is important both for their interaction with the GDP/GTP exchange proteins and for their activation of NADPH oxidase. 146 87

The Rac proteins, Rac1 and Rac2, are essential components of the NADPH oxidase system of phagocytes and regulate the actin assembly associated with membrane ruffling. These functions are controlled by the GTP-bound form of Rac. The biochemical interaction between Rac and its only known GDP-dissociation stimulator (termed smgGDS) was characterized. SmgGDS was able to stimulate the incorporation of guanosine 5'-[gamma-thio]-triphosphate GTP[gamma S] into the RhoA, Rac2, Rac1, Rap1A and CDC42Hs GTP-binding proteins, but the activity was greatest toward RhoA and Rac2. Isoprenoid modification of these proteins was not absolutely required for the interaction with smgGDS. Interestingly, the activity of smgGDS toward Rac1 could not be observed in a [3H]GDP/GTP exchange assay under conditions where it stimulated incorporation of GTP[gamma S] into Rac1. We determined that smgGDS prevented the loss of Rac1 activity during the [3H]GDP/GTP exchange assay by demonstrating the ability of smgGDS to inhibit the loss of Rac1 GTP[gamma S]-binding during incubations at 30 degrees C. This stabilizing effect was exactly counterbalanced by the ability of smgGDS to stimulate the release of [3H]GDP from Rac1, thereby producing no net observable effect in the exchange assay. SmgGDS was able to effectively stimulate the release of GDP but not GTP[gamma S] from Rac1. SmgGDS maintains Rac1 in a nucleotide-free form after release of GDP, indicating that the reaction between Rac1 and smgGDS involves a substituted enzyme mechanism.
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PMID:SmgGDS stabilizes nucleotide-bound and -free forms of the Rac1 GTP-binding protein and stimulates GTP/GDP exchange through a substituted enzyme mechanism. 798 Apr 44