scholarly journals Secondary organic material formed by methylglyoxal in aqueous aerosol mimics

2010 ◽  
Vol 10 (3) ◽  
pp. 997-1016 ◽  
Author(s):  
N. Sareen ◽  
A. N. Schwier ◽  
E. L. Shapiro ◽  
D. Mitroo ◽  
V. F. McNeill
Keyword(s):  
Organic Material ◽  
Aldol Condensation ◽  
Bimolecular Reaction ◽  
Ionization Mass ◽  
Aerosol Formation ◽  
Hydronium Ion ◽  
Rate Limiting Step ◽  
Tropospheric Aerosol ◽  
Heterogeneous Processes ◽  
Rate Limiting

Abstract. We show that methylglyoxal forms light-absorbing secondary organic material in aqueous ammonium sulfate and ammonium nitrate solutions mimicking tropospheric aerosol particles. The kinetics were characterized using UV-Vis spectrophotometry. The results suggest that the bimolecular reaction of methylglyoxal with an ammonium or hydronium ion is the rate-limiting step for the formation of light-absorbing species, with kNH4+II=5×10−6 M−1 min−1 and kH3O+II≤10−3 M−1 min−1. Evidence of aldol condensation products and oligomeric species up to 759 amu was found using chemical ionization mass spectrometry with a volatilization flow tube inlet (Aerosol-CIMS). Tentative identifications of carbon-nitrogen species and a sulfur-containing compound were also made using Aerosol-CIMS. Aqueous solutions of methylglyoxal, with and without inorganic salts, exhibit significant surface tension depression. These observations add to the growing body of evidence that dicarbonyl compounds may form secondary organic material in the aerosol aqueous phase, and that secondary organic aerosol formation via heterogeneous processes may affect seed aerosol properties.

A Dynamic Substrate is Required for MhuD-catalyzed Degradation of Heme to Mycobilin

2021 ◽  
Author(s):  
Biswash Thakuri ◽  
Bruce O'Rourke ◽  
Amanda Graves ◽  
Matthew Liptak
Keyword(s):  
Dynamic Equilibrium ◽  
Ionization Mass ◽  
Esi Ms ◽  
Enzymatic Mechanism ◽  
Single Turnover ◽  
Rate Limiting Step ◽  
Planar Substrate ◽  
Out Of Plane ◽  
Substrate Conformation ◽  
Rate Limiting

The non-canoncial heme oxygenase MhuD from <i>Mycobacterium tuberculosis</i> binds a heme substrate that adopts a dynamic equilibrium between planar and out-of-plane ruffled conformations. MhuD degrades this substrate to an unusual mycobilin product via successive monooxygenation and dioxygenation reactions. This article establishes a causal relationship between heme substrate dynamics and MhuD-catalyzed heme degradation resulting in a refined enzymatic mechanism. UV/Vis absorption (Abs) and electrospray ionization mass spectrometry (ESI-MS) data demonstrated that a second-sphere substitution favoring population of the ruffled heme conformation changed the rate-limiting step of the reaction resulting in a measurable build-up of the monooxygenated meso-hydroxyheme intermediate. In addition, UV/Vis Abs and ESI-MS data for a second-sphere variant that favored the planar substrate conformation showed that this change altered the enzymatic mechanism resulting in an alpha-biliverdin product. Single-turnover kinetic analyses for three MhuD variants revealed that the rate of heme monooxygenation depends upon the population of the ruffled substrate conformation. These kinetic analyses also revealed that the rate of meso-hydroxyheme dioxygenation by MhuD depends upon the population of the planar substrate conformation. Thus, the ruffled haem conformation supports rapid heme monooxygenation by MhuD, but further oxygenation to the mycobilin product is inhibited. In contrast, the planar substrate conformation exhibits altered heme monooxygenation regiospecificity followed by rapid oxygenation of meso-hydroxyheme. Altogether, these data yielded a refined enzymatic mechanism for MhuD where access to both substrate conformations is needed for rapid incorporation of three oxygen atoms into heme yielding mycobilin.<br>

The Kinetics of Reactions in and Near the Cytochrome b/f Complex of Chloroplast Thylakoids. I. Proton Deposition

1988 ◽  
Vol 15 (5) ◽  
pp. 695 ◽  
Author(s):  
AB Hope ◽  
J Liggins ◽  
DB Matthews
Keyword(s):  
Rate Constant ◽  
Bimolecular Reaction ◽  
Plastoquinone Pool ◽  
Rate Limiting Step ◽  
Fixed Concentration ◽  
Wide Range ◽  
Entropy Of Activation ◽  
Electron Donation ◽  
Rate Limiting ◽  
Kinetics Of

The kinetics of proton deposition in the intrathylakoid spaces of pea chloroplasts were measured under a wide range of conditions. With duroquinol added to reduce the plastoquinone pool, and 3-(3,4-dichlorophenyl)-1,1-dimethylurea added to inhibit photosystem II, but no ionophore present, the proton deposition, attributed to plastoquinol oxidation, was biphasic. About half the deposition had an apparent rate constant (k) of 150-200 s-1, the other half about 10 s-1. Valinomycin or nonactin (<0.1 �M) plus potassium ions made the deposition almost monophasic, with k = 140 s-1. When the state of reduction of the plastoquinone pool was varied by the addition of varied concentrations of duroquinol, in the presence of 1 �M nonactin, k for proton deposition varied from about 20 (0.01 mM duroquinol) up to a maximum of 140 s-1 (0.5 mM duroquinol). When temperature was varied between 4 and 23°C, with 1 �M nonactin, an Arrhenius plot of ln(k) for proton deposition was linear; the activation enthalpy was 67 kJ mol-1, the entropy of activation, 23 J K-1 mol-1. The data are analysed in terms of a bimolecular reaction between a varying concentration of plastoquinol and a fixed concentration of oxidised Rieske centre. The results are consistent with a rate constant, for the first electron donation by plastoquinol, of 28 s-1 (the rate-limiting step), followed by a relatively fast second electron donation to cytochrome b563 (low potential), followed by deposition of two protons. The speed of the second proton deposition is dependent on the membrane potential difference.

A Dynamic Substrate is Required for MhuD-catalyzed Degradation of Heme to Mycobilin

2020 ◽  
Author(s):  
Biswash Thakuri ◽  
Bruce O'Rourke ◽  
Amanda Graves ◽  
Matthew Liptak
Keyword(s):  
Dynamic Equilibrium ◽  
Ionization Mass ◽  
Esi Ms ◽  
Enzymatic Mechanism ◽  
Single Turnover ◽  
Rate Limiting Step ◽  
Planar Substrate ◽  
Out Of Plane ◽  
Substrate Conformation ◽  
Rate Limiting

The non-canoncial heme oxygenase MhuD from <i>Mycobacterium tuberculosis</i> binds a heme substrate that adopts a dynamic equilibrium between planar and out-of-plane ruffled conformations. MhuD degrades this substrate to an unusual mycobilin product via successive monooxygenation and dioxygenation reactions. This article establishes a causal relationship between heme substrate dynamics and MhuD-catalyzed heme degradation resulting in a revised enzymatic mechanism. UV/Vis absorption (Abs) and electrospray ionization mass spectrometry (ESI-MS) data demonstrated that a second-sphere substitution favoring population of the ruffled heme conformation changed the rate-limiting step of the reaction resulting in a measurable build-up of the monooxygenated meso-hydroxyheme intermediate. In addition, UV/Vis Abs and ESI-MS data for a second-sphere variant that favored the planar substrate conformation showed that this change altered the enzymatic mechanism resulting in an alpha-biliverdin product. Single-turnover kinetic analyses for three MhuD variants revealed that the rate of heme monooxygenation depends upon the population of the ruffled substrate conformation. These kinetic analyses also revealed that the rate of meso-hydroxyheme dioxygenation by MhuD depends upon the population of the planar substrate conformation. Thus, the ruffled haem conformation supports rapid heme monooxygenation by MhuD, but further oxygenation to the mycobilin product is inhibited. In contrast, the planar substrate conformation exhibits altered heme monooxygenation regiospecificity followed by rapid oxygenation of meso-hydroxyheme. Altogether, these data yielded a revised enzymatic mechanism for MhuD where access to both substrate conformations is needed for rapid incorporation of three oxygen atoms into heme yielding mycobilin.<br>

scholarly journals A Dynamic Substrate is Required for MhuD-catalyzed Degradation of Heme to Mycobilin

2020 ◽  
Author(s):  
Biswash Thakuri ◽  
Bruce O'Rourke ◽  
Amanda Graves ◽  
Matthew Liptak
Keyword(s):  
Dynamic Equilibrium ◽  
Ionization Mass ◽  
Esi Ms ◽  
Enzymatic Mechanism ◽  
Single Turnover ◽  
Rate Limiting Step ◽  
Planar Substrate ◽  
Out Of Plane ◽  
Substrate Conformation ◽  
Rate Limiting

The non-canoncial heme oxygenase MhuD from <i>Mycobacterium tuberculosis</i> binds a heme substrate that adopts a dynamic equilibrium between planar and out-of-plane ruffled conformations. MhuD degrades this substrate to an unusual mycobilin product via successive monooxygenation and dioxygenation reactions. This article establishes a causal relationship between heme substrate dynamics and MhuD-catalyzed heme degradation resulting in a revised enzymatic mechanism. UV/Vis absorption (Abs) and electrospray ionization mass spectrometry (ESI-MS) data demonstrated that a second-sphere substitution favoring population of the ruffled heme conformation changed the rate-limiting step of the reaction resulting in a measurable build-up of the monooxygenated meso-hydroxyheme intermediate. In addition, UV/Vis Abs and ESI-MS data for a second-sphere variant that favored the planar substrate conformation showed that this change altered the enzymatic mechanism resulting in an alpha-biliverdin product. Single-turnover kinetic analyses for three MhuD variants revealed that the rate of heme monooxygenation depends upon the population of the ruffled substrate conformation. These kinetic analyses also revealed that the rate of meso-hydroxyheme dioxygenation by MhuD depends upon the population of the planar substrate conformation. Thus, the ruffled haem conformation supports rapid heme monooxygenation by MhuD, but further oxygenation to the mycobilin product is inhibited. In contrast, the planar substrate conformation exhibits altered heme monooxygenation regiospecificity followed by rapid oxygenation of meso-hydroxyheme. Altogether, these data yielded a revised enzymatic mechanism for MhuD where access to both substrate conformations is needed for rapid incorporation of three oxygen atoms into heme yielding mycobilin.<br>

scholarly journals Secondary organic material formed by methylglyoxal in aqueous aerosol mimics – Part 1: Surface tension depression and light-absorbing products

2009 ◽  
Vol 9 (4) ◽  
pp. 15541-15565 ◽  
Author(s):  
A. N. Schwier ◽  
E. L. Shapiro ◽  
N. Sareen ◽  
V. F. McNeill
Keyword(s):  
Surface Tension ◽  
Organic Material ◽  
Aldol Condensation ◽  
Aerosol Particles ◽  
Ammonium Ion ◽  
Inorganic Salts ◽  
Solution Composition ◽  
Tropospheric Aerosol ◽  
Seed Aerosol ◽  
Nitrate Solutions

Abstract. We show that methylglyoxal forms light-absorbing secondary organic material in aqueous ammonium sulfate and ammonium nitrate solutions mimicking tropospheric aerosol particles. The light-absorbing products form on the order of minutes, and solution composition continues to change over several days. The results suggest an aldol condensation pathway involving the participation of the ammonium ion. Aqueous solutions of methylglyoxal, with and without inorganic salts, exhibit surface tension depression. Methylglyoxal uptake could potentially change the optical properties, climate effects, and heterogeneous chemistry of the seed aerosol over its lifetime.

scholarly journals A Dynamic Substrate is Required for MhuD-catalyzed Degradation of Heme to Mycobilin

2021 ◽  
Author(s):  
Biswash Thakuri ◽  
Bruce O'Rourke ◽  
Amanda Graves ◽  
Matthew Liptak
Keyword(s):  
Dynamic Equilibrium ◽  
Ionization Mass ◽  
Esi Ms ◽  
Enzymatic Mechanism ◽  
Single Turnover ◽  
Rate Limiting Step ◽  
Planar Substrate ◽  
Out Of Plane ◽  
Substrate Conformation ◽  
Rate Limiting

The non-canoncial heme oxygenase MhuD from <i>Mycobacterium tuberculosis</i> binds a heme substrate that adopts a dynamic equilibrium between planar and out-of-plane ruffled conformations. MhuD degrades this substrate to an unusual mycobilin product via successive monooxygenation and dioxygenation reactions. This article establishes a causal relationship between heme substrate dynamics and MhuD-catalyzed heme degradation resulting in a refined enzymatic mechanism. UV/Vis absorption (Abs) and electrospray ionization mass spectrometry (ESI-MS) data demonstrated that a second-sphere substitution favoring population of the ruffled heme conformation changed the rate-limiting step of the reaction resulting in a measurable build-up of the monooxygenated meso-hydroxyheme intermediate. In addition, UV/Vis Abs and ESI-MS data for a second-sphere variant that favored the planar substrate conformation showed that this change altered the enzymatic mechanism resulting in an alpha-biliverdin product. Single-turnover kinetic analyses for three MhuD variants revealed that the rate of heme monooxygenation depends upon the population of the ruffled substrate conformation. These kinetic analyses also revealed that the rate of meso-hydroxyheme dioxygenation by MhuD depends upon the population of the planar substrate conformation. Thus, the ruffled haem conformation supports rapid heme monooxygenation by MhuD, but further oxygenation to the mycobilin product is inhibited. In contrast, the planar substrate conformation exhibits altered heme monooxygenation regiospecificity followed by rapid oxygenation of meso-hydroxyheme. Altogether, these data yielded a refined enzymatic mechanism for MhuD where access to both substrate conformations is needed for rapid incorporation of three oxygen atoms into heme yielding mycobilin.<br>

scholarly journals Secondary organic material formed by methylglyoxal in aqueous aerosol mimics – Part 2: Product identification using Aerosol-CIMS

2009 ◽  
Vol 9 (4) ◽  
pp. 15567-15594 ◽  
Author(s):  
N. Sareen ◽  
E. L. Shapiro ◽  
A. N. Schwier ◽  
V. F. McNeill
Keyword(s):  
Ammonium Sulfate ◽  
Organic Material ◽  
Aldol Condensation ◽  
Critical Role ◽  
Negative Ion ◽  
Ionization Mass ◽  
Bulk Reaction ◽  
Product Identification ◽  
Negative Ion Mode ◽  
Sulfur Containing

Abstract. We used chemical ionization mass spectrometry with a volatilization flow tube inlet (Aerosol-CIMS) to characterize secondary organic material formed by methylglyoxal with ammonium sulfate in aqueous aerosol mimics. Bulk reaction mixtures were diluted and atomized to form submicron aerosol particles. Organics were detected using Aerosol-CIMS in positive and negative ion mode using I− and H3O+·(H2O)n as reagent ions. The results are consistent with aldol condensation products, carbon-nitrogen species, sulfur-containing compounds, and oligomeric species up to 759 amu. These results support previous observations by us and others that ammonium sulfate plays a critical role in the SOA formation chemistry of dicarbonyl compounds.

Ornithine Decarboxylase Activity in Cultured Endothelial Cells Stimulated by Serum, Thrombin and Serotonin

1978 ◽  
Vol 39 (02) ◽  
pp. 496-503 ◽  
Author(s):  
P A D’Amore ◽  
H B Hechtman ◽  
D Shepro
Keyword(s):  
Endothelial Cells ◽  
Ornithine Decarboxylase ◽  
Decarboxylase Activity ◽  
Aortic Endothelial Cells ◽  
Ornithine Decarboxylase Activity ◽  
Rate Limiting Step ◽  
Bovine Aortic Endothelial Cells ◽  
Limiting Step ◽  
Rate Limiting ◽  
Serum Serotonin

SummaryOrnithine decarboxylase (ODC) activity, the rate-limiting step in the synthesis of polyamines, can be demonstrated in cultured, bovine, aortic endothelial cells (EC). Serum, serotonin and thrombin produce a rise in ODC activity. The serotonin-induced ODC activity is significantly blocked by imipramine (10-5 M) or Lilly 11 0140 (10-6M). Preincubation of EC with these blockers together almost completely depresses the 5-HT-stimulated ODC activity. These observations suggest a manner by which platelets may maintain EC structural and metabolic soundness.

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