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M E Murphy

Publications and source records attributed to M E Murphy.

At least 19 recordsLinked to original sources
PubMed1996

Site-directed mutagenesis of azurin from Pseudomonas aeruginosa enhances the formation of an electron-transfer complex with a copper-containing nitrite reductase from Alcaligenes faecalis S-6.

Kinetic analysis of electron transfer between azurin from Pseudomonas aeruginosa and copper-containing nitrite reductase (NIR) from Akaligenes faecalis S-6 was carried out to investigate the specificity of electron transfer between copper-containing proteins. Apparent values of kcat and Km of NIR for azurin were 300-fold smaller and 172-fold larger than those for the physiological redox partner, pseudoazurin from A. faecalis S-6, respectively, suggesting that the electron transfer between azurin and NIR was less specific than that between pseudoazurin and NIR. One of the major differences in 3-D structure between these redox proteins, azurin and pseudoazurin, is the absence and presence of lysine residues near their type 1 copper sites, respectively. Three mutated azurins, D11K, P36K, and D11K/P36K, were constructed to evaluate the importance of lysine residues in the interaction with NIR. The redox potentials of D11K, P36K, and D11K/P36K azurins were higher than that of wild-type azurin by 48, 7, and 55 mV, respectively. As suggested by the increase in the redox potential, kinetic analysis of electron transfer revealed reduced ability of electron transfer in the mutated azurins. On the other hand, although each of the single mutations caused modest effects on the decrease in the Km value, the simultaneous mutations of D11K and P36K caused significant decrease in the Km value when compared to that for wild-type azurin. These results suggest that the introduction of two lysine residues into azurin facilitated docking to NIR.

Alcaligenes↗
PubMed1995

Apamin-sensitive K+ channels mediate an endothelium-dependent hyperpolarization in rabbit mesenteric arteries.

1. Vascular endothelial cells release a variety of substances which affect the membrane potential and tone of underlying vascular smooth muscle. In the presence of N omega-nitro-L-arginine to inhibit nitric oxide synthase and indomethacin to inhibit cyclo-oxygenase, acetylcholine (ACh; EC50 approximately 1 microM) elicited the release of an endothelium-derived hyperpolarizing factor (EDHF) in rabbit mesenteric arteries. 2. The hyperpolarization due to EDHF was blocked by apamin (IC50 approximately 0.3 nM), and by other inhibitors of the apamin-sensitive K+ channel (10 nM scyllatoxin, 100 microM d-tubocurarine, 300 microM gallamine) in the presence of indomethacin and N omega-nitro-L-arginine. The hyperpolarization was not blocked by glibenclamide (5 microM), iberiotoxin (10 nM), tetraethylammonium (1 mM), barium (500 microM), 4-aminopyridine (500 microM), ouabain (10 microM), bumetanide (10 microM), or nimodipine (100 nM). 3. In the presence of apamin and N omega-nitro-L-arginine, but the absence of indomethacin, ACh triggered a hyperpolarization that was blocked by glibenclamide, an inhibitor of ATP-sensitive K+ (KATP) channels. A similar glibenclamide-sensitive hyperpolarization was caused by Iloprost, a stable analogue of prostacyclin. 4. In experiments which distinguished the effects of EDHF, prostanoids and nitric oxide, hyperpolarizations and/or relaxations triggered by ACh were antagonized by muscarinic antagonists, the relative potencies (atropine approximately 4-DAMP > pirenzepine) of which indicated that the release of all three endothelium-derived factors was mediated by M3 receptors. 5. Our results suggest that ACh stimulates M3 receptors on endothelial cells, triggering the release of nitric oxide and prostanoids, which hyperpolarize underlying smooth muscle by activation of KATP channels, and the release of an EDHF, which hyperpolarizes smooth muscle through the activation of apamin-sensitive K+ (KAS) channels.

Acetylcholine↗
PubMed1995

Structure of Alcaligenes faecalis nitrite reductase and a copper site mutant, M150E, that contains zinc.

The structures at 2.0 and 2.25 A resolution of native and recombinant nitrite reductase from Alcaligenes faecalis show that they are identical to each other and very similar to nitrite reductase from Achromobacter cycloclastes. The crystallographic structure of a mutant, M150E, which unlike the wild-type protein cannot be reduced by pseudoazurin, shows that the glutamate replacement for methionine binds to a metal at the type I Cu site via only one oxygen. Anomalous scattering data collected at wavelengths of 1.040 and 1.377 A reveal that the metal at the type I site is a Zn. No significant differences from the native structure other than local perturbations at the type I site are seen. A local pseudo 2-fold axis relates the two domains of different monomers which form the active site. The two residues, Asp98 and His255, believed to be involved in catalysis are related by this 2-fold. An unusual (+)-(+) charge interaction between Lys269, Glu279, and His100 helps to orient the active site Cu ligand, His100. A number of negatively charged surface residues create an electrostatic field whose shape suggests that it may serve to direct incoming negatively charged nitrite as well as to dock the electron donor partner, pseudoazurin.

Alcaligenes↗
PubMed1995

Nitric oxide hyperpolarizes rabbit mesenteric arteries via ATP-sensitive potassium channels.

1. Nitric oxide (NO) relaxes vascular smooth muscle (VSM) by mechanisms which are not fully understood. One possibility is that NO hyperpolarizes membranes, thereby diminishing Ca2+ entry through voltage-dependent Ca2+ channels. In the current study, the effects of NO on membrane potential of rabbit mesenteric arteries were recorded using intracellular microelectrodes. 2. NO, released by 3-morpholinosydnonimine (SIN-1, 3 microM), reversibly hyperpolarized arteries by -9.5 +/- 4.0 mV (means +/- S.D., n = 97) from a resting membrane potential of -53.1 +/- 5.7 mV. The hyperpolarization was blocked by oxyhaemoglobin (20 microM), and only occurred in arteries pre-treated with N omega-nitro-L-arginine (100 microM) or denuded of endothelium. 3. The effect of SIN-1 was concentration dependent (EC50 approximately 0.4 microM) and its dose response was shifted to the left by zaprinast (100 microM), an inhibitor of cGMP-specific phosphodiesterases. 4. The hyperpolarization due to SIN-1 was modified by changes in extracellular K+ concentration, but not by changes in Ca2+, Na+ or Cl-. The hyperpolarization was blocked by glibenclamide (IC50 approximately 0.15 microM), but not by apamin (3-300 nM), barium (5-150 microM), tetraethylammonium (0.1-10 mM), or 4-aminopyridine (5-500 microM). The hyperpolarization due to lemakalim (0.03-3 microM), an activator of ATP-sensitive potassium channels (KATP), displayed the same sensitivities to these K+ channel blocking agents, whereas the endothelium-derived hyperpolarizing factor, triggered by the addition of acetylcholine (3 microM), caused a hyperpolarization (-15.3 +/- 6.2 mV) that was blocked by apamin, but not by any other agent. 5. These results suggest that NO hyperpolarizes VSM in rabbit mesenteric arteries by activating KATP channels, with the accumulation of cGMP as an intermediate step.

Adenosine Triphosphate↗
PubMed1995

Replacements in a conserved leucine cluster in the hydrophobic heme pocket of cytochrome c.

A cluster of highly conserved leucine side chains from residues 9, 68, 85, 94, and 98 is located in the hydrophobic heme pocket of cytochrome c. The contributions of two of these, Leu 85 and Leu 94, have been studied using a protein structure-function-mutagenesis approach to probe their roles in the maintenance of overall structural integrity and electron transfer activity. Structural studies of the L85C, L85F, L85M, and L94S mutant proteins show that, in each case, the overall fold of cytochrome c is retained, but that localized conformational shifts are required to accommodate the introduced side chains. In particular, the side chains of Cys 85 and Phe 85 form energetically favorable interactions with Phe 82, whereas Met 85 takes on a more remote conformation to prevent an unfavorable interaction with the phenyl ring of Phe 82. In the case of the L94S mutant protein, the new polar group introduced is found to form hydrogen bonds to nearby carbonyl groups. In all proteins with substitutions at Leu 85, the hydrophobic nature of the heme pocket is preserved and no significant decrease in heme reduction potential is observed. Despite earlier predictions that Leu 85 is an important determinant in cytochrome c electron transfer partner complexation, our studies show this is unlikely to be the case because the considerable surface contour perturbations made by substitutions at this residue do not correspondingly translate into significant changes in electron transfer rates. For the L94S mutant protein, the substitution of a polar hydroxyl group directly into the hydrophobic heme pocket has a larger effect on heme reduction potential, but this is mitigated by two factors. First, the side chain of Ser 94 is rotated away from the heme group and, second, the side chain of Leu 98 shifts into a portion of the new space available, partially shielding the heme group. The Leu 94 Ser substitution does not perturb the highly conserved interface formed by the nearly perpendicular packing of the N- and C-terminal helices of cytochrome c, ruling this out as the cause of this mutant protein becoming thermally labile and having a lower functional activity. Our results show these effects are most likely attributable to disruption of the heme pocket region. Much of the ability of cytochrome c to absorb the introduction of mutations at Leu 85 and Leu 94 appears to be a consequence of the conformational flexibility afforded by the leucine cluster in this region as well as the presence of a nearby internal cavity.(ABSTRACT TRUNCATED AT 400 WORDS)

Crystallography, X-Ray↗
PubMed1994

X-ray structure and site-directed mutagenesis of a nitrite reductase from Alcaligenes faecalis S-6: roles of two copper atoms in nitrite reduction.

Nitrite reductase (NIR) from the denitrifying bacterium Alcaligenes faecalis S-6 is a copper-containing enzyme which requires pseudoazurin, a low molecular weight protein containing a single type I copper atom, as a direct electron donor in vivo. Crystallographic analysis shows that NIR is a trimer composed of three identical subunits, each of which contains one atom of type I copper and one atom of type II copper, and that the ligands to the type I and type II copper atoms are the same as those of the Achromobacter cycloclastes NIR. An efficient NIR expression-secretion system in Escherichia coli was constructed and used for site-directed mutagenesis. An NIR mutant with a replacement of the type II copper ligand, His135, by Lys still retained a type II copper site as well as a type I copper atom, but it completely lost nitrite-reducing activity as measured with methyl viologen as an electron donor. On the other hand, another mutant with a replacement of the type I copper ligand, Met150, by Glu contained only a type II copper atom, but it still retained significant nitrite-reducing activity with methyl viologen. When pseudoazurin was used as an electron donor for the reaction, however, Met150Glu failed to catalyze the reduction of nitrite. Kinetic analysis of the electron transfer between NIR and pseudoazurin revealed that the electron-transfer rate between Met150Glu and pseudoazurin was reduced 1000-fold relative to that of wild-type NIR.(ABSTRACT TRUNCATED AT 250 WORDS)

Alcaligenes↗
PubMed1994

Loss of chromosome 8p sequences in human breast carcinoma cell lines.

Cytogenetic and molecular analyses of human breast cancer cells have identified consistent losses of specific chromosomal regions in these tumors, suggesting that such regions harbor tumor suppressor genes whose homozygous loss or inactivation directly contributes to tumorigenesis. To date, deletions of chromosome 8 sequences have been described infrequently and only in low percentages of breast carcinomas. We report the identification of a new DNA marker on chromosome 8p that is deleted in 6 (75%) of 8 breast carcinoma cell lines and in 1 primary breast carcinoma examined. No deletion of this marker was detected in any normal or nonbreast carcinoma cell lines analyzed. Southern blot and fluorescence in situ hybridization studies indicate that this clone maps to chromosome 8 between bands p12 and p21. These observations suggest that a new gene, whose loss or inactivation may foster breast carcinoma tumorigenesis, may reside in this chromosome 8p region.

Base Sequence↗
PubMed1993

The structure and function of omega loop A replacements in cytochrome c.

The structural and functional consequences of replacing omega-loop A (residues 18-32) in yeast iso-1-cytochrome c with the corresponding loop of Rhodospirillum rubrum cytochrome c2 have been examined. The three-dimensional structure of this loop replacement mutant RepA2 cytochrome c, and a second mutant RepA2(Val 20) cytochrome c in which residue 20 was back substituted to valine, were determined using X-ray diffraction techniques. A change in the molecular packing is evident in the RepA2 mutant protein, which has a phenylalanine at position 20, a residue considerably larger than the valine found in wild-type yeast iso-1-cytochrome c. The side chain of Phe 20 is redirected toward the molecular surface, altering the packing of this region of omega-loop A with the hydrophobic core of the protein. In the RepA2(Val 20) structure, omega-loop A contains a valine at position 20, which restores the original wild-type packing arrangement of the hydrophobic core. Also, as a result of omega-loop A replacement, residue 26 is changed from a histidine to asparagine, which results in displacements of the main-chain atoms near residue 44 to which residue 26 is hydrogen bonded. In vivo studies of the growth rate of the mutant strains on nonfermentable media indicate that the RepA2(Val 20) cytochrome c behaves much like the wild-type yeast iso-1 protein, whereas the stability and function of the RepA2 cytochrome c showed a temperature dependence. The midpoint reduction potential measured by cyclic voltammetry of the RepA2 mutant is 271 mV at 25 degrees C. This is 19 mV less than the wild-type and RepA2(Val 20) proteins (290 mV) and may result from disruption of the hydrophobic packing in the heme pocket and increased mobility of omega-loop A in RepA2 cytochrome c. The temperature dependence of the reduction potential is also greatly enhanced in the RepA2 protein.

Amino Acid Sequence↗
PubMed1993

Dietary amino acid complementation as a foraging strategy for wild birds.

Foraging birds finding foods containing protein of various quality could satisfy their amino acid needs by either 1) choosing only those foods that contain a suitable array of essential amino acids, or 2) choosing foods in amounts that permit complementation of constituent amino acids. We studied the abilities of sparrows (Zonotrichia leuchophrys gambelii) to use dietary amino acid complementation as a foraging strategy. We conducted two series of tests: 1) to determine if sparrows could select adequate portions from food pairs in order to compensate for reciprocal dietary deficiencies of either valine and lysine or lysine and threonine, and 2) to evaluate to what extent fortuitous (passive) complementation of dietary amino acids was constrained in sparrows by the magnitude of the dietary amino acid deficiency and the schedule of daily intakes of complementary foods. Small birds appear to have limited abilities to actively exploit dietary amino acid complementation. Birds offered a choice of two foods deficient in either lysine, valine, or threonine but of complementary compositions, reduced their daily intakes of food and body masses, but to a lesser extent (ca. one-half to one-third, and ca. one-quarter as much, respectively) than when either of the deficient foods were offered alone. Even passive complementation of dietary amino acids was severely constrained by both the magnitude of the dietary amino acid deficiency and the time course of feeding. The greater the amino acid deficiency, the less effective the complementation of dietary amino acids. The time course for effective and efficient complementation of dietary essential amino acids in these small, metabolically active animals was less than 2 h.

Amino Acids↗
PubMed1993

Urinary oxalate and glycolate excretion patterns in the first year of life: a longitudinal study.

To determine the range of normal values, we studied urinary excretion of oxalate and glycolate prospectively and longitudinally in a cohort of 30 healthy term infants. Random urine samples were obtained at 2 days, 2 weeks, and 2, 4, 6, and 9 months of age. The results had a log-normal distribution. The mean oxalate/creatinine ratio, as determined by the oxalate oxidase method, was 0.08 (in milligrams of oxalate to milligrams of creatinine) with a normalized range of 0.02 to 0.31. The mean ratio when oxalates were measured by using the Olthuis assay was 0.13 (range 0.03 to 0.53). The mean glycolate/creatinine ratio was 0.07 (range 0.02 to 0.26). These values did not correlate with increasing age. The oxalate/creatinine ratios were higher in formula-fed infants than in those who were fed human milk (0.14 +/- 0.16 vs 0.08 +/- 0.04; p < 0.01).

Creatinine↗
PubMed1993

Urolithiasis in pediatric patients.

Urolithiasis in pediatric patients has been perceived as uncommon, and the appropriate evaluation and management have been controversial. To determine the clinical characteristics, types of stone problems, and outcomes of pediatric patients with urolithiasis encountered in a referral center, we retrospectively assessed 221 patients (113 girls and 108 boys) with urolithiasis examined at the Mayo Clinic between 1965 and 1987. The median age at onset of symptoms was 11 6/12 years among the female patients and 10 6/12 years among the male patients. Analysis of stone constituents in 122 patients showed the proportion of calcium oxalate (44.7%), calcium phosphate (23.6%), and cystine (8.1%) stones to be similar in all age-groups. Overall, struvite stones were found in 17.1% and uric acid stones in 1.6% of patients. Conditions that predisposed to metabolic urolithiasis were identified in 115 patients (52%). Hypercalciuria was confirmed in 49 of 145 patients (33.8%) and hyperoxaluria in 25 of 124 (20.2%). Eight of 96 patients had hyperuricosuria, and 5 of 54 had hypocitraturia. Forty-one patients (18.6%) had infection-related stones. Of 66 patients with structural anomalies of the genitourinary tract, 24 (36%) had metabolic abnormalities and 26 (39%) had chronic infection. Among patients with chronic infection, 29% had metabolic abnormalities. Of the 221 patients, 148 (67%) had two or more stones during a mean follow-up of 59 months. Among 140 patients with 12 months or more of follow-up, metabolic activity was present in 31 (22.1%) at the time of most recent examination. Overall, 166 of 221 children (75.1%) were found to have factors that predisposed to urolithiasis.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1993

Nitric oxide and superoxide in cultured cells: limited production and influence on DNA synthesis.

The ability of superoxide (O2-) and NO to influence DNA synthesis, as estimated by [3H]thymidine incorporation in logarithmically growing cells, was evaluated in three human cell types: embryonic lung fibroblasts, skin fibroblasts, and mesangial cells. Nontoxic rates of O2- generation (0.2 nM/min-0.2 microM/min) only slightly stimulated DNA synthesis in mesangial cells (10-13% increase) and did not affect fibroblast DNA synthesis. Nontoxic rates of NO generation (0.1-10 microM/min) also had only limited effects, inhibiting DNA synthesis in lung and skin fibroblasts slightly (10-20% decrease) but not affecting mesangial cells. In all three cell types, neither O2- nor NO was generated at high enough endogenous rates to support an autocrinic regulation of DNA synthesis. This and other lines of evidence indicate that a reaction between O2- and NO is unlikely to account for their opposing effects on DNA synthesis.

Cells↗
PubMed1992

Protection by glutathione and other thiol compounds against the loss of protein thiols and tocopherol homologs during microsomal lipid peroxidation.

Microsomes from rat liver were used to investigate the mechanisms by which thiol compounds protect cellular membranes against damage from oxidants. Glutathione (GSH), dihydrolipoate and dithioerythritol, but not cysteine, ameliorated the loss of thiol groups of microsomal proteins attacked by Fe/ADP/NADPH or Fe/ADP/ascorbate prooxidant systems. The protection by GSH, but not dihydrolipoate or dithioerythritol, appeared to be enzymic since it was lost after microsomes were heated or treated with trypsin. The blocking of microsomal protein thiols with N-ethylmaleimide also diminished the protective effect of GSH. Lipid peroxidation, as assessed by chemiluminescence and vitamin-E loss, was inhibited in parallel with the protection of protein thiols. In microsomes lacking vitamin E, the protection of protein thiols by exogenous thiols was diminished. However, the GSH-dependent protection of vitamin E showed no preference for alpha-tocopherol over other tocopherol homologs. It is suggested that a GSH-dependent enzyme maintains protein thiols in the face of oxidative damage during microsomal peroxidation. A maintenance of protein thiols might not only protect important metabolic functions, but may also afford an antioxidant capacity to membranes, and account for one facet of the GSH-dependent inhibition of lipid peroxidation.

Adenosine Diphosphate↗
PubMed1992

Structure determination and analysis of yeast iso-2-cytochrome c and a composite mutant protein.

As part of a study of protein folding and stability, the three-dimensional structures of yeast iso-2-cytochrome c and a composite protein (B-2036) composed of primary sequences of both iso-1 and iso-2-cytochromes c have been solved to 1.9 A and 1.95 A resolutions, respectively, using X-ray diffraction techniques. The sequences of iso-1 and iso-2-cytochrome c share approximately 84% identity and the B-2036 composite protein has residues 15 to 63 from iso-2-cytochrome c with the rest being derived form the iso-1 protein. Comparison of these structures reveals that amino acid substitutions result in alterations in the details of intramolecular interactions. Specifically, the substitution Leu98Met results in the filling of an internal cavity present in iso-1-cytochrome c. Further substitutions of Val20Ile and Cys102Ala alter the packing of secondary structure elements in the iso-2 protein. Blending the isozymic amino acid sequences in this latter area results in the expansion of the volume of an internal cavity in the B-2036 structure to relieve a steric clash between Ile20 and Cys102. Modification of hydrogen bonding and protein packing without disrupting the protein fold is illustrated by the His26Asn and Asn63Ser substitutions between iso-1 and iso-2-cytochromes c. Alternatively, a change in main-chain fold is observed at Gly37 apparently due to a remote amino acid substitution. Further structural changes occur at Phe82 and the amino terminus where a four residue extension is present in yeast iso-2-cytochrome c. An additional comparison with all other eukaryotic cytochrome c structures determined to date is presented, along with an analysis of conserved water molecules. Also determined are the midpoint reduction potentials of iso-2 and B-2036 cytochromes c using direct electrochemistry. The values obtained are 286 and 288 mV, respectively, indicating that the amino acid substitutions present have had only a small impact on the heme reduction potential in comparison to iso-1-cytochrome c, which has a reduction potential of 290 mV.

Amino Acid Sequence↗
PubMed1992

Antioxidant depletion in aortic crossclamping ischemia: increase of the plasma alpha-tocopheryl quinone/alpha-tocopherol ratio.

To assess whether oxidative stress contributes to the ischemia/reperfusion injury of aortic surgery, the contents of alpha-tocopherol, alpha-tocopheryl quinone, ascorbate, lipid-derived malondialdehyde, protein thiols, cholesterol, and lactate were analyzed in plasma samples from 24 patients subjected to aortic crossclamping. alpha-Tocopherol, ascorbate, and protein thiols decreased during ischemia, whereas alpha-tocopheryl quinone increased in all but two cases, doubling on average in proportion to alpha-tocopherol. Upon reperfusion alpha-tocopherol, ascorbate, and protein thiols remained low, whereas alpha-tocopheryl quinone returned to the preischemic level. Lipid-derived malondialdehyde (a measure of lipid hydroperoxides) increased significantly only during reperfusion. The results suggest that oxidative stress occurs simultaneously with ischemia/reperfusion during aortic surgery, and that measurement of the tocopheryl quinone/tocopherol ratio may shed new light on the underlying pathological events.

Aged↗
PubMed1991

Reversible conversion of nitroxyl anion to nitric oxide by superoxide dismutase.

Superoxide dismutase (SOD) rapidly scavenges superoxide (O2-) and also prolongs the vasorelaxant effects of nitric oxide (NO), thought to be the endothelium-derived relaxing factor. This prolongation has been ascribed to prevention of the reaction between O2- with NO. We report that SOD supports a reversible reduction of NO to NO-. When cyanamide and catalase were used to generate NO- in the presence of SOD, NO was measured by the conversion of HbO2 to MetHb. When SOD[Cu(I)] was exposed to NO anaerobically, NO- was trapped by MetHb forming nitrosylmyoglobin. When NO was generated by 3-morpholinosydnonimine hydrochloride in the presence of SOD, NO- or a similar reductant was formed, which reduced catalase compound II and promoted the formation of the catalase [Fe(III)]-NO complex. It is, therefore, conceivable that SOD may protect NO and endothelium-derived relaxing factor by a mechanism in addition to O2- scavenging and that NO- may be a physiologically important form of endothelium-derived relaxing factor.

Animals↗
PubMed1991

Nitric oxide production by cultured aortic endothelial cells in response to thiol depletion and replenishment.

The requirements and influence of thiols on the production of nitric oxide (NO) were examined in cultured porcine aortic endothelial cells. NO production was diminished when cells were pretreated with thiol-depleting agents (IC50: N-ethylmaleimide, 30 microM; 1-chloro-2,4-dinitrobenzene, 200 microM; diamide, 1.5 mM; diethyl maleate, 20 mM). The depletion of glutathione (45-99% loss at the various IC50 values) and protein thiols (3-25% loss at IC50) showed no consistent relationship to decreased NO production. The effects of the agents on NO production were not linked to altered sensitivity to the stimulant (calcium ionophore A23187; maximal effect at 10 microM), but roughly paralleled the appearance of cell damage (17-44% lactate dehydrogenase release at IC50). The decrease in NO production due to 1-chloro-2,4-dinitrobenzene was partially reversed by cysteine, dithioerythritol, and dihydrolipoate, whereas cystine partially reversed the decrease due to diamide or diethyl maleate. On the other hand, several thiols diminished NO production in control cells. Overall, alterations of NO production did not parallel the depletion or replenishment of either glutathione, protein thiol, or soluble thiol pools, and so the results argue against hypotheses that cellular thiols are either substrates or necessary cofactors in the pathway of NO synthesis in endothelial cells.

Animals↗