Effect of Solution Viscosity on Intramolecular Electron Transfer in Sulfite Oxidase

Feng, Changjian; Kedia, Rohit V.; Hazzard, James T.; Hurley, John K.; Tollin, Gordon; Enemark, John H.

doi:10.1021/bi016059f

Cited by 116 publications

(189 citation statements)

References 46 publications

(54 reference statements)

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“…Recent studies of mammalian SOX kinetics showed that the IET rate was impacted by solution viscosity (13,14), confirming the hypothesis that the Cyt b domain was undergoing a large conformational change during catalysis relative to the Mo-MPT-containing sulfite-oxidizing module (9). NaR has a similar structure to SOX in that the Cyt b domain is tethered to the Mo-MPT-containing nitrate-reducing module via a flexible "hinge" sequence.…”

mentioning

confidence: 65%

“…The k cat values were calculated based on the Mo-MPT content when available or normalized to known values (1,2,11,12). No K m determinations were done, because it has been shown that this parameter was independent of the viscosity for some enzymes (14,17) and it was assumed that all of the forms would be impacted to the same degree.…”

Section: Resultsmentioning

confidence: 99%

“…1 and Table I), the interpretation of the results is clearly more difficult than for enzymes with a single flexible hinge region such as mammalian SOX and yeast flavocytochrome b 2 (13,14,31). However, it is clear that IET in NaR is gated by large conformational changes of the Cyt b domain relative to the electrondonating and nitrate-reducing modules of the enzyme, which is illustrated in Scheme 1, where the gating effects of the two hinges are grouped together.…”

Section: Resultsmentioning

confidence: 99%

“…As is described below, we have taken advantage of the collection of recombinant NaR fragments already available to characterize Hinge 2 effects in relation to viscosity. Laser flash photolysis has been used to directly study IET in mammalian SOX where the Cyt b heme-Fe was rapidly reduced and the effect of viscosity on the equilibration of the electron with the Mo-MPT center was observed (14). Although laser flash photolysis would be useful to show a direct effect of viscosity on NaR IET, there would be complexity to the results because NaR has more redox centers than SOX.…”

Section: Resultsmentioning

confidence: 99%

“…The k cat observed in the viscosity studies was shown to follow a linear dependence on the negative power of the viscosity and was described by Kramers equation (Equation 1) (14,(17)(18)(19)(20)(21),…”

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confidence: 99%

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Viscosity Effects on Eukaryotic Nitrate Reductase Activity

Barbier¹,

Campbell²

2005

Journal of Biological Chemistry

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Rate-limiting processes of catalysis by eukaryotic molybdenum-containing nitrate reductase (NaR, EC 1.7.1.1-3) were investigated using two viscosogens (glycerol and sucrose) and observing their impact on NAD-(P)H:NaR activity of corn leaf NaR and recombinant Arabidopsis and yeast NaR. Holo-NaR has two "hinge" sequences between stably folded regions housing its internal electron carriers: 1) Hinge 1 between the molybdenum-containing nitrate reducing module and cytochrome b domain containing heme and 2) Hinge 2 between cytochrome b and cytochrome b reductase (CbR) module containing FAD. Solution viscosity negatively impacted the activity of these holo-NaR forms, which suggests that the rate-limiting events in catalysis were likely to involve large conformational changes that restrict or "gate" internal electron-proton transfers (IET). Little effect of viscosity was observed on recombinant CbR module and methyl viologen nitrate reduction by holo-NaR, suggesting that these activities involved no large conformational changes. To determine whether Hinge 2 is involved in gating the first step in IET, the effects of viscosogen on cytochrome c and ferricyanide reductase activities of holo-NaR and ferricyanide reductase activity of the recombinant molybdenum reductase module (CbR, Hinge 2, and cytochrome b) were analyzed. Solution viscosity negatively impacted these partial activities, as if Hinge 2 were involved in gating IET in both enzyme forms. We concluded that both Hinges 1 and 2 appear to be involved in gating IET steps by restricting the movement of the cytochrome b domain relative to the larger nitrate-reducing and electron-donating modules of NaR.

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mentioning

confidence: 65%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

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Viscosity Effects on Eukaryotic Nitrate Reductase Activity

Barbier¹,

Campbell²

2005

Journal of Biological Chemistry

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Assembly ofMoco inMo/WEnzymes

Leimkühler

2017

Encyclopedia of Inorganic and Bioinorganic Chemistry

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The biosynthesis of the molybdenum cofactor (Moco) is ubiquitous and highly conserved in all organisms from bacteria to humans. In Moco, the molybdenum atom is coordinated to a dithiolene group present in the pterin‐based 6‐alkyl side chain of molybdopterin (MPT). In general, the biosynthesis of Moco can be divided into three steps in eukaryotes, and four steps in bacteria and archaea: (i) the starting point is the formation of the cPMP from 5′GTP, (ii) in the second step MPT is formed by the insertion of two sulfur molecules into cPMP, (iii) in the third step the molybdenum atom is inserted into MPT and Moco is formed, and (iv) additional modification of Moco occurs in bacteria and archaea in a fourth step by the attachment of nucleotides (CMP or GMP) to the phosphate group of MPT, forming the dinucleotide variants of Moco. Further, small differences exist in Moco formation among the different phyla. In higher eukaryotes Moco biosynthesis is located in different cellular compartments, many individual Moco biosynthesis proteins appear to have several cellular roles, and some proteins are shared between different biosynthetic pathways. Further, bacteria contain a large variety of more than 60 different molybdoenzymes being involved in specific, however, usually nonessential redox reactions. In contrast, in humans only four different molybdoenzymes have been identified, and a defect in Moco biosynthesis is lethal due to the loss of sulfite oxidase activity. This review will focus on the biosynthesis of Moco in bacteria and humans.

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Are Environmentally Coupled Enzymatic Hydrogen Tunneling Reactions Influenced by Changes in Solution Viscosity?

et al. 2007

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The role and importance of protein dynamics in enzymatic reactions remains a key question in enzymology. [1][2][3][4][5] Of great current interest is whether enzymes have evolved to use quantum tunneling to the best advantage by, when necessary, coupling specific protein motions (vibrations) to the tunneling reaction coordinate. It is now widely accepted that H tunneling (proton, hydrogen, or hydride) occurs in enzymecatalyzed reactions, [1,[6][7][8][9][10][11] but the role of promoting motions in modulating the tunneling barrier remains contentious. [3] Experimental identification of coupled (promoting) motions is challenging, with experimental evidence for environmentally coupled H-tunneling reactions mainly inferred from the unusual temperature dependence of primary kinetic isotope effects (KIEs). [12][13][14][15] In addition to temperature, [12,13] there are other intensive (bulk) properties that, in principle, can be used to probe these reactions, including pressure [10,16] and solution viscosity. [17][18][19][20][21] We have demonstrated the utility of combining pressure and temperature to study environmentally coupled H tunneling in the reductive half-reaction (RHR) of morphinone reductase (MR), involving hydride tunneling from the coenzyme NADH to the enzyme-bound cofactor flavin mononucleotide (FMN).[10] Although changes in solution viscosity have been used to probe protein rearrangement after CO dissociation from myoglobin, [21] configurational and conformational gating of interprotein electron-transfer (ET) reactions, [17][18][19][20] and conformational gating of intraprotein ET, [22] studies of the dynamical influence of solvent viscosity on enzymatic H-tunneling reactions are less common. Moreover, there has been no rigorous quantitative analysis of these effects.At a phenomenological level, we have shown that the magnitude and temperature dependence of the reaction rate and KIE measured for proton tunneling in the RHR of methylamine dehydrogenase (MADH) are unchanged following the addition of 30 % glycerol (viscosity increase ca. 2-3-fold) to the reaction solution.[12] Similarly, a decrease in KIE and increase in apparent enthalpy for the RHR of l-phenylalanine oxidase (PAO) upon the addition of 30 % glycerol has been reported.[23] Glycosylation of a protein surface can also affect the dynamic motion of a protein, and this approach has been used to study the rate of hydride transfer in glucose oxidase (GO) [24,25] by 1) using various glycoforms of the enzyme that differ in the extent of glycosylation [24] and 2) replacing the native polysaccharide with different polymeric forms of polyethylene glycol.[25] By both increasing and decreasing the apparent surface viscosity, decreases in the fitness of the enzyme were observed, reducing the Arrhenius pre-exponential ratio (A D /A T ) for deuterium and tritium transfer away from unity. [24,25] GO, MADH, and PAO do not have strongly temperature-dependent KIEs, suggesting a minor role (if any) for fast, non-equilibrated promoting motions coupled to the H-tr...

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Effect of Solution Viscosity on Intramolecular Electron Transfer in Sulfite Oxidase

Cited by 116 publications

References 46 publications

Viscosity Effects on Eukaryotic Nitrate Reductase Activity

Viscosity Effects on Eukaryotic Nitrate Reductase Activity

Assembly ofMoco inMo/WEnzymes

Are Environmentally Coupled Enzymatic Hydrogen Tunneling Reactions Influenced by Changes in Solution Viscosity?

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