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M K Richards

Publications and source records attributed to M K Richards.

10 recordsLinked to original sources
PubMed1996

Characterization of C415 mutants of neuronal nitric oxide synthase.

Nitric oxide synthase (NOS) catalyzes the oxidation of L-arginine to citrulline and nitric oxide. C415H and C415A mutants of the neuronal isoform of NOS (nNOS) were expressed in a baculovirus system and purified to homogeneity for spectral analysis and activity measurements. UV-visible spectra of each mutant lacked an observable Soret peak, suggesting that neither mutant contained heme. When reduced in the presence of CO, however, a small Soret centered at 417 nm could be detected for the C415H mutant, further supporting the assignment of C415 as the axial ligand to the heme. In addition to a deficiency in bound heme, neither mutant had any detectable bound tetrahydrobiopterin, as compared to wild-type enzyme, which had a ratio of 0.84 mol of bound pteridine:1 mol of nNOS 160 kDa subunit. The C415H mutant contained bound FAD and FMN at levels of 1.0 +/- 0.1 and 0.9 +/- 0.1 mol/mol of nNOS subunit, respectively. UV-visible spectra of both nNOS mutants retained the distinctive absorbance due to tightly associated oxidized flavin prosthetic groups. Further, the spectra suggested the presence of a neutral flavin semiquinone. Ferricyanide oxidation of the C415A mutant yielded a spectrum that was essentially that of oxidized flavin. Ferricyanide titration showed that the C415A mutant contained approximately 1 reducing equiv. Circular dichroism spectra suggested that each mutant was folded properly, in that both spectra were found to be essentially identical to the spectrum of wild-type nNOS. Neither mutant could synthesize nitric oxide, and neither mutant had the ability to oxidize NADPH unless an exogenous electron acceptor was added. The rate of cytochrome c reduction by each mutant was found to be slightly less, but very similar to the rate (approximately 20 mumol mg-1 min-1) observed with wild-type nNOS. In all cases, the rate of cytochrome c reduction increased approximately 15-fold with the addition of calmodulin. Overall, these spectral and activity data suggest that C415 is the axial heme ligand and that a point mutation at C415 prevents binding of heme and tetrahydrobiopterin without interfering with the global folding or the reductase function of nNOS.

Amino Acid Sequence↗
PubMed1996

Stunting is associated with overweight in children of four nations that are undergoing the nutrition transition.

A higher risk of obesity in stunted children has been described in Hispanic-American, Jamaican and Andean populations, but little systematic exploration has been done concerning this area in nutrition. This paper examines the relationship between stunting and overweight status for children aged 3-6 and 7-9 y in nationally representative surveys in Russia, Brazil, and the Republic of South Africa and a large nationwide survey in China. Using identical cut-offs for body mass index, the prevalence of child overweight in these countries ranges from 10.5 to 25.6% (based on the 85th percentile); recent NHANES III results indicate that this prevalence is around 22% in the U.S. Stunting is also common in the surveyed countries affecting 9.2-30.6% of all children. Our results showed a significant association between stunting and overweight status in children of all countries. The income-adjusted risk ratios of being overweight for a stunted child ranged from 1.7 to 7.8. Clearly, there is an important association between stunting and high weight-for-height in a variety of ethnic environmental and social backgrounds. Although the underlying mechanisms remain unexplored, this association has serious public health implications particularly for lower income countries. As these countries enter the nutrition transition experiencing large changes in dietary and activity patterns, they may face, among other problems, additional difficulties in their fight against obesity.

Body Mass Index↗
PubMed1995

Lung sources and cytokine requirements for in vivo expression of inducible nitric oxide synthase.

Products of inducible nitric oxide synthase (iNOS) are known to be involved in lung injury following intrapulmonary deposition of immunoglobulin G immune complexes (IgG-ICx). In the current studies rat alveolar macrophages stimulated in vitro with murine interferon gamma (IFN-gamma), tumor necrosis factor alpha, interleukin 1 alpha, (IL-1 alpha), lipopolysaccharide (LPS), or IgG-ICx immunostained for iNOS and produced nitrite/nitrate- (NO2-/NO3-) in a dose- and time-dependent manner requiring availability of L-arginine. Under the same conditions, IL-4 and IL-10 reduced NO2-/NO3- generation. Type II alveolar epithelial cells, which were obtained from normal rat lungs and stimulated in vitro with IgG-ICx, LPS, or IFN-gamma, also immunostained for iNOS and generated NO2-/NO3-. Special techniques of bronchoalveolar lavage (BAL) were used to retrieve alveolar macrophages and type II alveolar epithelial cells. Under these conditions, intrapulmonary deposition of LPS yielded BAL fluids containing increased amounts of NO2-/NO3- and macrophages that spontaneously released NO2-/NO3- and stained for iNOS. After intrapulmonary deposition of IgG both macrophages as well as type II cells (retrieved by BAL) spontaneously produced NO2-/NO3- and both cell types immunostained for iNOS (approximately 20% of all type II cells and 35% of all alveolar macrophages). Using dual fluorescence staining for cell identification, frozen sections of lung tissue after IgG immune complex deposition revealed iNOS in both alveolar macrophages and type II cells. Finally, in the immune complex model of alveolitis, the appearance of iNOS in macrophages as well as macrophage production in vitro of NO2-/NO3- was dependent on the in vivo availability of tumor necrosis factor alpha, IL-1, and IFN-gamma. These studies suggest a dual cell source for nitric oxide in inflamed lungs and the requirements for iNOS of several cytokines.

Amino Acid Oxidoreductases↗
PubMed1994

Characterization of neuronal nitric oxide synthase and a C415H mutant, purified from a baculovirus overexpression system.

Nitric oxide synthase (NOS) catalyzes the conversion of L-arginine to citrulline and nitric oxide (.NO). A baculovirus overexpression system has been developed for a constitutive NOS isoform, cloned originally from rat cerebellum (B-NOS). Recombinant virus was used at a multiplicity of infection of 5 to infect Spodoptera frugiperda cells in culture, and NOS was expressed to 10% of the total soluble protein at 48 h postinfection. In order to express catalytically active enzyme, it was necessary to supplement the culture media with hemin. This increased the activity of the enzyme 7-fold. A two column affinity purification was developed for the recombinant enzyme, which gave homogeneous protein that migrated at 150 kDa on a denaturing polyacrylamide gel. A Km for L-arginine was determined to be 2.0 +/- 0.4 microM. As isolated, recombinant B-NOS exhibited a Soret maximum at 402 nm, which shifted to 394 nm in the presence of L-arginine. The Soret maximum of the reduced enzyme in the presence of CO was 444 nm. Initial rate steady-state kinetic analysis of the recombinant B-NOS showed evidence of substrate inhibition by L-arginine, which could also be seen in a partially purified preparation of B-NOS from rat cerebella. This substrate inhibition was not observed with the inducible isoform of NOS, purified from immunostimulated murine macrophages. A C415H mutant was overexpressed and purified using the same conditions established for the wild-type recombinant B-NOS. This C415H mutant exhibited no activity and did not bind heme, providing the first experimental evidence to support previously reported primary amino acid comparisons which suggest that C415 provides the coordinating thiolate to the heme moiety in B-NOS.

Amino Acid Oxidoreductases↗
PubMed1991

Inactivation of macrophage nitric oxide synthase activity by NG-methyl-L-arginine.

.N = O synthase catalyzes the oxidation of one of the two chemically equivalent guanido nitrogens of L-arginine to nitric oxide (.N = O). NG-Methyl-L-arginine has been previously characterized as a potent competitive inhibitor of both major types of .N = O synthases. Initial rate kinetics were performed with a spectrophotometric assay based on the oxidation of oxy- to methemoglobin by .N = O. NG-Methyl-L-arginine was a competitive inhibitor of .N = O synthase activity derived from activated murine macrophages with a Ki of 6.2 microM. When the enzyme was pre-incubated in the presence of the required cofactors NADPH and tetrahydrobiopterin, time- and concentration-dependent irreversible inactivation of the activity was observed. At 37 degrees C the kinact was 0.050 min-1. This inactivation process exhibited substrate protection, saturation kinetics and required the cofactors necessary for enzymatic turnover. These data indicate that NG-methyl-L-arginine acts as a mechanism-based enzyme inactivator of murine macrophage .N = O synthase.

Animals↗
PubMed1991

Rapid analysis of glycolipid anchors in amphiphilic dimers of acetylcholinesterases.

1. We describe two simple procedures for the rapid identification of certain structural features of glycolipid anchors in acetylcholinesterases (AChEs). 2. Treatment with alkaline hydroxylamine (that cleaves ester-linked acyl chains but not ether-linked alkyl chains) converts molecules possessing a diacylglycerol, but not those with an alkylacylglycerol, into hydrophilic derivatives. AChEs in human and bovine erythrocytes possess an alkylacylglycerol (Roberts et al., J. Biol. Chem. 263:18766-18775, 1988; Biochem. Biophys. Res. Commun. 150:271-277, 1988) and are not converted to hydrophilic dimers by alkaline hydroxylamine. Amphiphilic dimers of AChE from Drosophila, from mouse erythrocytes, and from the human erythroleukaemia cell line K562 also resist the treatment with hydroxylamine and likely possess a terminal alkylacylglycerol. This indicates that the cellular pool of free glycolipids used as precursors of protein anchors is distinct from the pool of membrane phosphatidylinositols (which contain diacylglycerols). 3. Pretreatment with alkaline hydroxylamine is required to render the amphiphilic AChE from human erythrocytes susceptible to digestion by Bacillus thuringiensis phosphatidylinositol-specific phospholipase C (PI-PLC) (Toutant et al., Eur. J. Biochem. 180:503-508, 1989). We show here that this is also the case for the AChE from mouse erythrocytes, which therefore likely possesses an additional acyl chain in the anchor that prevents the action of PI-PLC. 4. In two sublines of K562 cells (48 and 243), we observed that AChE either was directly susceptible to PI-PLC (243) or required a prior deacylation by alkaline hydroxylamine (48). This suggests that glycolipid anchors in AChE of K562-48 cells, but not those in AChE of K562-243 cells, contain the additional acylation demonstrated in AChE from human erythrocytes. These observations illustrate the cell specificity (and the lack of species-specificity) of the structure of glycolipid anchors.

Acetylcholinesterase↗
PubMed1991

Novel avermectins produced by mutational biosynthesis.

Avermectins with a wide range of novel C-25 substituents have been prepared by feeding carboxylic acids or their biosynthetic precursors to a Streptomyces avermitilis mutant strain ATCC 53568. This organism lacks the ability to form isobutyric and S-2-methylbutyric acids from their 2-oxo acid precursors and thus is unable to produce natural avermectins unless supplied with these acids. The novel avermectins produced by mutational biosynthesis possess broad-spectrum antiparasitic activity.

Animals↗
PubMed1990

Molecular forms of acetylcholinesterase in two sublines of human erythroleukemia K562 cells. Sensitivity or resistance to phosphatidylinositol-specific phospholipase C and biosynthesis.

Acetylcholinesterase (AChE) in K562 cells exists in two molecular forms. The major form, an amphiphilic dimer (G2a) which sediments at 5.3 S, and the minor form, an amphiphilic monomer (G1a) which sediments at 3.5 S. Extraction in the presence of the sulfhydryl alkylating agent N-ethylmaleimide was required to preserve the G2a form. In Triton X-100 extracts of the subline K562-243, phosphatidylinositol-specific phospholipase C (PtdIns-PLC) from Bacillus thuringiensis converted most of the G2a AChE into a hydrophilic dimer (G2h), indicating that the G2a form possessed a hydrophobic glycoinositol phospholipid that mediated its attachment to the membrane. Treatment of intact K562-243 cells with PtdIns-PLC released approximately 60% of the total AChE activity and provided an estimate of the externally exposed AChE. The direct conversion from an amphiphilic to a hydrophilic dimeric form by PtdIns-PLC was not obtained in extracts or intact cells of the subline K562-48. Instead, pretreatment with alkaline hydroxylamine was necessary to render the amphiphilic G2 form of this subline susceptible to digestion by the phospholipase. In this respect, the amphiphilic dimer of K562-48 AChE resembles the G2a form of human erythrocyte AChE, which is resistant to PtdIns-PLC because of the direct palmitoylation of an inositol hydroxyl group in the anchor [Roberts et al. (1988) J. Biol. Chem. 263, 18766-18775]. Release of this acyl chain by hydroxylamine renders the enzyme susceptible to PtdIns-PLC [Toutant et al. (1989) Eur. J. Biochem. 180, 503-508]. In both K562 sublines, sialidase decreased the migration of the G2a form but not of the G1a form of AChE. G1a forms thus appear to represent an intracellular pool of newly synthesized molecules residing in a compartment proximal to the trans-Golgi apparatus. The sialidase-resistant G1a molecules were also resistant to PtdIns-PLC digestion; possible explanations for this resistance are presented.

Acetylcholinesterase↗
PubMed1990

The immune response to myelin proteolipid protein in the Lewis rat: identification of the immunodominant B cell epitope.

The polyclonal antibody response of the Lewis rat to bovine myelin proteolipid protein (PLP) has been investigated following immunisation with either the purified protein or bovine central nervous system myelin. In both situations, the carboxyl-terminal sequence of PLP was identified as the immunodominant domain of this protein and epitope mapping demonstrated that the carboxyl-terminal amino acid, phenylalanine276, was a critical requirement for antibody recognition of this epitope. This single epitope accounted for approximately 78% and 56% of the antibody response to PLP in rats immunised with PLP or bovine myelin, respectively. Polyclonal rat antibodies specific for this carboxyl terminal epitope of PLP were also obtained following immunisation with a synthetic 20 amino acid oligopeptide analogue of the carboxyl-terminal sequence of PLP. Western blotting demonstrated this antibody response was specific for the PLP and DM-20 components of mammalian central nervous system myelin. In contrast, no major PLP epitopes were detected within the PLP amino acid sequences 35-58 and 91-150, the other major hydrophilic domains of this protein.

Amino Acid Sequence↗