The NADPH oxidase of phagocytic leukocytes.
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Flavins↗
Biomedical subjects
K P Shatwell
Publications and source records attributed to K P Shatwell.
Intramembrane bis-heme motif for transmembrane electron transport conserved in a yeast iron reductase and the human NADPH oxidase.
A plasma membrane iron reductase, required for cellular iron acquisition by Saccharomyces cerevisiae, and the human phagocytic NADPH oxidase, implicated in cellular defense, contain low potential plasma membrane b cytochromes that share elements of structure and function. Four critical histidine residues in the FRE1 protein of the iron reductase were identified by site-directed mutagenesis. Individual mutation of each histidine to alanine eliminated the entire heme spectrum without affecting expression of the apoprotein, documenting the specificity of the requirement for the histidine residues. These critical residues are predicted to coordinate a bis-heme structure between transmembrane domains of the FRE1 protein. The histidine residues are conserved in the related gp91(phox) protein of the NADPH oxidase of human granulocytes, predicting the sites of heme coordination in that protein complex. Similarly spaced histidine residues have also been implicated in heme binding by organelle b cytochromes with little overall sequence similarity to the plasma membrane b cytochromes. This bis-heme motif may play a role in transmembrane electron transport by distinct families of polytopic b cytochromes.
Alleles↗
The FRE1 ferric reductase of Saccharomyces cerevisiae is a cytochrome b similar to that of NADPH oxidase.
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.
Amino Acid Sequence↗
NADPH oxidase.
Superoxide is instrumental in the killing of microorganisms by phagocytic cells. It is generated by the NADPH oxidase system, a membrane-bound electron transport complex which pumps electrons from NADPH in the cytoplasm across the wall of the phagocytic vacuole to molecular oxygen. Superoxide deficiency results in the genetically inherited condition Chronic Granulomatous Disease (CGD), in which the patient is abnormally susceptible to infection. In recent years many of the underlying genetic defects in CGD have been identified and are providing important insights into the structure and mechanism of the NADPH oxidase complex.
Electron Transport↗
Cloning, sequencing, and expression of the araE gene of Klebsiella oxytoca 8017, which encodes arabinose-H+ symport activity.
Southern analysis of the genomic DNA from species of the family Enterobacteriaceae, using a probe derived from the Escherichia coli araE gene, which encodes an arabinose-H+ symporter, detected araE in Salmonella, Citrobacter, Klebsiella, and Enterobacter spp. The Klebsiella oxytoca araE gene was cloned, sequenced, and expressed to compare its properties with those of araE from E. coli.
Amino Acid Sequence↗
Influence of acetyl and pyruvate substituents on the solution properties of xanthan polysaccharide.
Xanthan, an exocellular polysaccharide produced by the plant pathogenic bacterium Xanthomonas campestris has been the subject of considerable interest in recent years because of its unusual rheological properties in solution ('weak gel') and consequent range of applications. The polymer consists of a cellulosic backbone with trisaccharide side chains linked to alternate backbone residues; acetyl and pyruvate substituents are carried in variable amounts on these side chains. In this study a series of xanthans differing in the percentage of substituent groups and in molecular weight range have been prepared by culturing a variety of different strains of X. campestris. All of the xanthans have been characterized by a range of physicochemical techniques. In particular, the intrinsic viscosities at low shear rates, and at a range of ionic strengths, have been determined and the geometric persistence lengths evaluated by the Smidsrød-Haug method. Intensity light scattering measurements have been made using the procedure of Coviello and co-workers to promote molecular dispersion. Despite significant differences in the acetyl and pyruvate contents, the molecular weight vs mean square radius behaviour of our samples did not differ substantially from each other or from those reported for other xanthan samples in the literature. The persistence length, determined by the method of Schmidt et al. (120 +/- 8 nm) was also, within experimental error, the same for all the samples measured. These values differed considerably from those calculated from the ionic strength dependence of intrinsic viscosity (the Smidsrød-Haug method) was reported by Tinland and Rinaudo and calculated for our samples.(ABSTRACT TRUNCATED AT 250 WORDS)
Acetates↗
Polysaccharide strong and weak gels.
Small deformation oscillatory shear measurements have enabled a distinction to be made between so-called "strong" and "weak" gels, in particular those formed from biologically significant polysaccharides. At small enough strains, both systems give essentially the same mechanical spectrum, with G' > G", and with both moduli largely independent of frequency. However, the deformation dependence of the two classes of materials is very different. Strong gels are essentially strain independent (linearly viscoelastic) for strains of greater than about 0.25, whereas weak gels show such a response only for strains of less than about 0.05. At large deformations strong gels will rupture and fail, and will never "heal" without melting and resetting. Conversely, weak gels will recover and can flow without fracture, giving a power law response, with an exponent approaching -1, so-called "yield stress" behavior. The rheological properties of a strong gel, agarose, derived from the Rhodophyceae (marine algae) and a weak gel xanthan, an exocellular slime exuded by bacteria of the genus Xanthomonas, are measured in vitro, and related to in vivo requirements.
Biopolymers↗