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2 [methionine synthase]-methylcob(III)alamin + 2 S-adenosyl-L-homocysteine + NADP+ = 2 [methionine synthase]-cob(II)alamin + NADPH + H+ + 2 S-adenosyl-L-methionine
2 [methionine synthase]-methylcob(III)alamin + 2 S-adenosyl-L-homocysteine + NADP+ = 2 [methionine synthase]-cob(II)alamin + NADPH + H+ + 2 S-adenosyl-L-methionine

under anaerobic growth conditions, oxidized ferredoxin (flavodoxin):NADP+ oxidoreductase accepts a hydride from NADPH and transfers the electron to flavodoxin, generating primarily flavodoxin semiquinone. Under anaerobic conditions the decarboxylation of pyruvate is coupled to reduction of flavodoxin, forming the flavodoxin hydroquinone. These reduced forms of flavodoxin bind to inactive cob(II)alamin enzyme, causing a conformational change that is coupled with dissociation of His759 and protonation of the His759-Asp757-Ser810 triad. Although NADPH oxidation ultimately produces 2 equivalent of flavodoxin semiquinone, only one electron is transferred to methionine synthase during reductive methylation
-
2 [methionine synthase]-methylcob(III)alamin + 2 S-adenosyl-L-homocysteine + NADP+ = 2 [methionine synthase]-cob(II)alamin + NADPH + H+ + 2 S-adenosyl-L-methionine
mechanism for the NADPH-catalyzed reduction of diflavin oxidoreductases, overview
2 [methionine synthase]-methylcob(III)alamin + 2 S-adenosyl-L-homocysteine + NADP+ = 2 [methionine synthase]-cob(II)alamin + NADPH + H+ + 2 S-adenosyl-L-methionine
hydride transfer and interflavin electron transfer are two catalytic steps represented by two distinct kinetic phases leading to transient formation of the FAD hydroquinone
2 [methionine synthase]-methylcob(III)alamin + 2 S-adenosyl-L-homocysteine + NADP+ = 2 [methionine synthase]-cob(II)alamin + NADPH + H+ + 2 S-adenosyl-L-methionine
-
-
-
-
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2 [methionine synthase]-cob(II)alamin + NADPH + H+ + 2 S-adenosyl-L-methionine
2 [methionine synthase]-methylcob(I)alamin + 2 S-adenosylhomocysteine + NADP+
-
-
-
?
2 [methionine synthase]-methylcob(I)alamin + 2 S-adenosylhomocysteine + NADP+
2 [methionine synthase]-cob(II)alamin + NADPH + H+ + 2 S-adenosyl-L-methionine
[methionine synthase]-cob(II)alamin + NADH + S-adenosyl-L-methionine
[methionine synthase]methylcob(I)alamin + S-adenosylhomocysteine + NAD+
-
-
-
-
?
[Methionine synthase]-cob(II)alamin + NADPH + S-adenosyl-L-methionine
?
[Methionine synthase]-cob(II)alamin + NADPH + S-adenosyl-L-methionine
[Methionine synthase]methylcob(I)alamin + S-adenosylhomocysteine + NADP+
[methionine synthase]-cob(II)alamin + NADPH + S-adenosylmethionine
[methionine synthase]-methylcob(I)alamin + NADPH + S-adenosylhomocysteine
-
in presence of methionine synthase reductase, holoenzyme formation from apomethionine synthase and methylcobalamin is significantly enhanced due to stabilization of apomethionine synthase. In addition to reductase activity, methionine synthase reductase serves as a special chaperone for methionine synthase. It also has reductase activity for the reaction of aquacobalamin to cob(II)alamin
-
-
?
[methionine synthase]-cob(II)alamin + S-adenosyl-L-methionine + 2,6-dichlorophenolindophenol
[methionine synthase]methylcob(I)alamin + S-adenosylhomocysteine + ?
-
-
-
?
[methionine synthase]-cob(II)alamin + S-adenosyl-L-methionine + 3-acetylpyridine adenine dinucleotide phosphate
[methionine synthase]methylcob(I)alamin + S-adenosylhomocysteine + ?
-
-
-
?
[methionine synthase]-cob(II)alamin + S-adenosyl-L-methionine + doxorubicin
[methionine synthase]methylcob(I)alamin + S-adenosylhomocysteine + ?
-
-
-
?
[methionine synthase]-cob(II)alamin + S-adenosyl-L-methionine + ferricyanide
[methionine synthase]methylcob(I)alamin + S-adenosylhomocysteine + ?
-
-
-
?
[methionine synthase]-cob(II)alamin + S-adenosyl-L-methionine + menadione
[methionine synthase]methylcob(I)alamin + S-adenosylhomocysteine + ?
-
-
-
?
[methionine synthase]-methylcob(I)alamin + S-adenosylhomocysteine + NADP+
[methionine synthase]-cob(II)alamin + NADPH + S-adenosyl-L-methionine
additional information
?
-
2 [methionine synthase]-methylcob(I)alamin + 2 S-adenosylhomocysteine + NADP+

2 [methionine synthase]-cob(II)alamin + NADPH + H+ + 2 S-adenosyl-L-methionine
-
-
-
?
2 [methionine synthase]-methylcob(I)alamin + 2 S-adenosylhomocysteine + NADP+
2 [methionine synthase]-cob(II)alamin + NADPH + H+ + 2 S-adenosyl-L-methionine
the enzyme catalyzes the oxidation of NADPH and shuttles electrons via its FAD and FMN cofactors to inactive MScob(II)alamin
-
-
?
2 [methionine synthase]-methylcob(I)alamin + 2 S-adenosylhomocysteine + NADP+
2 [methionine synthase]-cob(II)alamin + NADPH + H+ + 2 S-adenosyl-L-methionine
the enzyme transfers reducing equivalents from NADPH via an FAD and FMN cofactor to a redox partner protein. hydride transfer from NADPH to FAD requires displacement of a conserved tryptophan that lies coplanar to the FAD isoalloxazine ring
-
-
?
[Methionine synthase]-cob(II)alamin + NADPH + S-adenosyl-L-methionine

?
-
the enzyme is involved in reductive activation of methionine synthase:
-
-
?
[Methionine synthase]-cob(II)alamin + NADPH + S-adenosyl-L-methionine
?
the enzyme is involved in reductive activation of methionine synthase:
-
-
?
[Methionine synthase]-cob(II)alamin + NADPH + S-adenosyl-L-methionine
?
patients of the cblE complementation group of disorders of folate/cobalamin metabolism who are defective in reductive activation of methionine synthase exhibit megablastic anemia, developmental delay, hyperhomocysteinemia, and hypomethioninemia
-
-
?
[Methionine synthase]-cob(II)alamin + NADPH + S-adenosyl-L-methionine

[Methionine synthase]methylcob(I)alamin + S-adenosylhomocysteine + NADP+
-
-
-
-
?
[Methionine synthase]-cob(II)alamin + NADPH + S-adenosyl-L-methionine
[Methionine synthase]methylcob(I)alamin + S-adenosylhomocysteine + NADP+
-
-
?
[methionine synthase]-methylcob(I)alamin + S-adenosylhomocysteine + NADP+

[methionine synthase]-cob(II)alamin + NADPH + S-adenosyl-L-methionine
-
-
-
-
r
[methionine synthase]-methylcob(I)alamin + S-adenosylhomocysteine + NADP+
[methionine synthase]-cob(II)alamin + NADPH + S-adenosyl-L-methionine
-
MSR is a NADPH-dependent diflavin oxidoreductase required for the reductive regeneration of catalytically inert cob(II)alamin to cob(I)alamin, complex formation between the substrate's activation domain and MSR, and the substrate's activation domain and the isolated FMN-binding domain of MSR. Weshow that the MS activation domain interacts directly with the FMN-binding domain of MSR, overview
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-
r
[methionine synthase]-methylcob(I)alamin + S-adenosylhomocysteine + NADP+
[methionine synthase]-cob(II)alamin + NADPH + S-adenosyl-L-methionine
-
interaction of the enzyme with the substrate enzyme methionine synthase via the C-terminal domain involves the residues K987 and K1071, interaction with substrate mutants K987T and K1071T is affected, structure-function relationship, overview
-
-
r
[methionine synthase]-methylcob(I)alamin + S-adenosylhomocysteine + NADP+
[methionine synthase]-cob(II)alamin + NADPH + S-adenosyl-L-methionine
-
MSR is a flavoprotein that regenerates the active form of cobalamin-dependent methionine synthase
-
-
r
additional information

?
-
difference in the relative efficiency of the very common polymorphic variant of the enzyme, I22M, suggests a molecular mechanism underlying the risk associated wiith the M22 allele for mild hyperhomocysteinemia
-
-
?
additional information
?
-
-
difference in the relative efficiency of the very common polymorphic variant of the enzyme, I22M, suggests a molecular mechanism underlying the risk associated wiith the M22 allele for mild hyperhomocysteinemia
-
-
?
additional information
?
-
-
biological implications of an attenuated mechanism of MS reactivation by MSR on methionine and folate metabolism, overview
-
-
?
additional information
?
-
-
the enzyme catalyzes also the inhibition of reduction of cytochrome c3+
-
-
?
additional information
?
-
the enzyme catalyzes the reduction of cytochrome c3+ with NADPH and NADH
-
-
?
additional information
?
-
-
the enzyme catalyzes the reduction of cytochrome c3+ with NADPH and NADH
-
-
?
additional information
?
-
the enzyme catalyzes the reduction of cytochrome c3+ with NADPH and NADH
-
-
?
additional information
?
-
fully reduced enzyme reaction with excess of cytochrome c, kinetics, overview. The NADPH-bound, fully reduced MSR completes most of its first turnover within the mixing dead time of the instrument, leaving only approximately 28% of the first turnover observable
-
-
?
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2 [methionine synthase]-cob(II)alamin + NADPH + H+ + 2 S-adenosyl-L-methionine
2 [methionine synthase]-methylcob(I)alamin + 2 S-adenosylhomocysteine + NADP+
-
-
-
?
2 [methionine synthase]-methylcob(I)alamin + 2 S-adenosylhomocysteine + NADP+
2 [methionine synthase]-cob(II)alamin + NADPH + H+ + 2 S-adenosyl-L-methionine
-
-
-
?
[Methionine synthase]-cob(II)alamin + NADPH + S-adenosyl-L-methionine
?
[methionine synthase]-methylcob(I)alamin + S-adenosylhomocysteine + NADP+
[methionine synthase]-cob(II)alamin + NADPH + S-adenosyl-L-methionine
additional information
?
-
[Methionine synthase]-cob(II)alamin + NADPH + S-adenosyl-L-methionine

?
-
the enzyme is involved in reductive activation of methionine synthase:
-
-
?
[Methionine synthase]-cob(II)alamin + NADPH + S-adenosyl-L-methionine
?
the enzyme is involved in reductive activation of methionine synthase:
-
-
?
[Methionine synthase]-cob(II)alamin + NADPH + S-adenosyl-L-methionine
?
patients of the cblE complementation group of disorders of folate/cobalamin metabolism who are defective in reductive activation of methionine synthase exhibit megablastic anemia, developmental delay, hyperhomocysteinemia, and hypomethioninemia
-
-
?
[methionine synthase]-methylcob(I)alamin + S-adenosylhomocysteine + NADP+

[methionine synthase]-cob(II)alamin + NADPH + S-adenosyl-L-methionine
-
-
-
-
r
[methionine synthase]-methylcob(I)alamin + S-adenosylhomocysteine + NADP+
[methionine synthase]-cob(II)alamin + NADPH + S-adenosyl-L-methionine
-
MSR is a NADPH-dependent diflavin oxidoreductase required for the reductive regeneration of catalytically inert cob(II)alamin to cob(I)alamin, complex formation between the substrate's activation domain and MSR, and the substrate's activation domain and the isolated FMN-binding domain of MSR. Weshow that the MS activation domain interacts directly with the FMN-binding domain of MSR, overview
-
-
r
additional information

?
-
difference in the relative efficiency of the very common polymorphic variant of the enzyme, I22M, suggests a molecular mechanism underlying the risk associated wiith the M22 allele for mild hyperhomocysteinemia
-
-
?
additional information
?
-
-
difference in the relative efficiency of the very common polymorphic variant of the enzyme, I22M, suggests a molecular mechanism underlying the risk associated wiith the M22 allele for mild hyperhomocysteinemia
-
-
?
additional information
?
-
-
biological implications of an attenuated mechanism of MS reactivation by MSR on methionine and folate metabolism, overview
-
-
?
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FAD

-
-
FAD
-
contains both FAD and FMN. The values of the midpoint potentials are -236 mV FAD oxidized/semiquinone and -264 mV FAD semiquinone/hydroquinone, variant M22/S175
FAD
-
contains both FAD and FMN. The values of the midpoint potentials are -252 mV FAD oxidized/semiquinone and -285 mV FAD semiquinone/hydroquinone, variant I22/L175
FAD
-
dual flavoprotein with an equimolar concentration of FAD, 0.9 mol per mol of enzyme, and FMN, 1.1 mol per mol of enzyme
FAD
-
midpoint reduction potential
FAD
-
MSR contains one FAD and one FMN cofactor per polypeptide and functions in the sequential transfer of reducing equivalents from NADPH to MS via its flavin centers
FAD
the enzyme is a diflavin oxidoreductase, binding structure, overview
FAD
a dual-flavin reductase
FAD
the C-terminal domain of MTRR binds FAD
FAD
the proximal FAD histidine residue accelerates proton-coupled electron transfer from FADH2 to the higher potential FMN
FMN

-
FMN
-
contains both FAD and FMN. The values of the midpoint potentials are -103 mV FMN oxidized/semiquinone and -175 mV FMN semiquinone/hydroquinone, variant I22/L175
FMN
-
contains both FAD and FMN. The values of the midpoint potentials are -114 mV FMN oxidized/semiquinone and -212 mV FMN semiquinone/hydroquinone, variant M22/S175
FMN
-
dual flavoprotein with an equimolar concentration of FAD, 0.9 mol per mol of enzyme, and FMN, 1.1 mol per mol of enzyme
FMN
-
midpoint reduction potential
FMN
-
MSR contains one FAD and one FMN cofactor per polypeptide and functions in the sequential transfer of reducing equivalents from NADPH to MS via its flavin centers
FMN
the enzyme is a diflavin oxidoreductase, binding structure, overview
FMN
a dual-flavin reductase
FMN
the N-terminal domain of MTRR binds flavin mononucleotide
FMN
the proximal FAD histidine residue accelerates proton-coupled electron transfer from FADH2 to the higher potential FMN
NADH

-
under anaerobic growth conditions, oxidized ferredoxin (flavodoxin):NADP+ oxidoreductase accepts a hydride from NADPH and transfers the electron to flavodoxin, generating primarily flavodoxin semiquinone. Under anaerobic conditions the decarboxylation of pyruvate is coupled to reduction of flavodoxin, forming the flavodoxin hydroquinone. These reduced forms of flavodoxin bind to inactive cob(II)alamin enzyme, leading to a conformational change that is coupled with dissociation of His759 and protonation of the His759-Asp757-Ser810 triad. Although NADPH oxidation ultimately produces 2 equivalent of flavodoxin semiquinone, only one electron is transferred to methionine synthase during reductive methylation
NADH
-
can replace NADPH but only at significantly higher and nonphysiological concentrations
NADP+

-
-
NADP+
binding structure, overview
NADP+
-
dependent on, binding structure, overview, the NADP+-bound FNR-like module of MSR spans the NADP(H)-binding domain, the FAD-binding domain, the connecting domain, and part of the extended hinge region
NADPH

-
-
NADPH
-
preferred electron donor
NADPH
-
dependent on, binding structure, overview, the NADP+-bound FNR-like module of MSR spans the NADP(H)-binding domain, the FAD-binding domain, the connecting domain, and part of the extended hinge region
additional information

-
NAD(H) is a poor cofactor
-
additional information
a riboflavin-dependent enzyme
-
additional information
mechanism of NADPH reduction of a diflavin enzyme, overview
-
additional information
-
mechanism of NADPH reduction of a diflavin enzyme, overview
-
additional information
structure-based analysis of the cofactor domain interfaces, overview
-
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0.0023 - 0.0038
2,6-dichlorophenolindophenol
0.0177 - 0.018
3-acetylpyridine adenine dinucleotide phosphate
0.0286 - 0.0366
doxorubicin
0.663 - 0.774
ferricyanide
additional information
additional information
-
0.0023
2,6-dichlorophenolindophenol

variant I22/S175
0.0038
2,6-dichlorophenolindophenol
variant I22/S175
0.0177
3-acetylpyridine adenine dinucleotide phosphate

variant I22/S175
0.018
3-acetylpyridine adenine dinucleotide phosphate
variant I22/S175
0.0286
doxorubicin

variant I22/S175
0.0366
doxorubicin
variant I22/S175
0.663
ferricyanide

variant I22/S175
0.774
ferricyanide
variant I22/S175
0.0177
menadione

variant I22/S175
0.018
menadione
variant I22/S175
0.0024
NADPH

pH 7.5, 25°C, recombinant wild-type enzyme
0.00289
NADPH
-
pH 7.5, 25°C
0.0062
NADPH
pH 7.5, 25°C, recombinant mutant A312Q
0.015
NADPH
pH 7.5, 25°C, recombinant mutant A312H
additional information
additional information

-
isothermal titration calorimetry reveals a binding constant of 0.037 and 0.002 mM for binding of NADP+ and 2',5'-ADP, respectively, for the ligand-protein complex formed with full-length MSR or the isolated FNR module
-
additional information
additional information
-
lack of control on the thermodynamics and kinetics of electron transfer in MSR, overview
-
additional information
additional information
steady-state kinetics analysis of wild-type and mutant enzymes with cytochrome c3+ and NADPH as substrates, overview
-
additional information
additional information
-
steady-state kinetics analysis of wild-type and mutant enzymes with cytochrome c3+ and NADPH as substrates, overview
-
additional information
additional information
steady-state kinetics analysis of wild-type and mutant enzymes with cytochrome c3+ and NADPH as substrates, overview
-
additional information
additional information
stopped-flow and steady-state kinetic analysis
-
additional information
additional information
-
stopped-flow and steady-state kinetic analysis
-
additional information
additional information
stopped-flow spectroscopy, single turnover methods and a kinetic model relating electron flux through the enzyme to its conformational setpoint and its rates of conformational switching, kinetic model for electron flux through a dual-flavin enzyme, overview
-
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0.0001 - 0.0014
2',5'-ADP
additional information
additional information
-
steady-state inhibition studies
-
0.0001
2',5'-ADP

pH 7.5, 25°C, mutant W697F, with cytochrome c3+
0.0007
2',5'-ADP
pH 7.5, 25°C, mutant W697Y, with cytochrome c3+
0.0014
2',5'-ADP
pH 7.5, 25°C, wild-type enzyme
0.0014
2',5'-ADP
-
inhibition of reduction of cytochrome c3+
0.003
NADP+

pH 7.5, 25°C, mutant W697F, with cytochrome c3+
0.0042
NADP+
pH 7.5, 25°C, mutant W697Y, with cytochrome c3+
0.0291
NADP+
pH 7.5, 25°C, recombinant mutant A312Q
0.036
NADP+
-
inhibition of reduction of cytochrome c3+
0.0369
NADP+
pH 7.5, 25°C, recombinant wild-type enzyme
0.037
NADP+
pH 7.5, 25°C, wild-type enzyme
0.0729
NADP+
pH 7.5, 25°C, recombinant mutant A312H
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malfunction

-
the c.56+781 A>C (rs326119) variant of intron-1 of MTRR significantly increases the risk of congenital heart disease in the Han Chinese population and is highly related to septation defects. The c.56+781 C allele profoundly decreases MTRR transcription. Phenotype, overview
malfunction
analysis of correlations of single nucleotide polymorphisms and various malformation anomalies, overview
metabolism

-
the MTRR gene is involved in tumorigenesis by regulating DNA methylation through activation of methionine synthase
metabolism
the enzyme enzyme plays a key role in homocysteine metabolism
physiological function

-
methionine synthase reductase is essential for the adequate remethylation of homocysteine, which is the dominant pathway for homocysteine removal during early embryonic development
physiological function
methionine synthase reductase, a diflavin oxidoreductase, plays a vital role in methionine and folate metabolism by sustaining methionine synthase activity
physiological function
roles of methionine synthase, MS, and methylenetetrahydrofolate reductase, MTHFR, and methionine synthase reductase, MTRR, in the folate cycle and homocysteine remethylation, overview
additional information

-
genotyping for the A66G polymorphism and analysis of the association with cancer risk reveals that the G allele and GG variant genotypes are associated with a significantly increased cancer risk
additional information
effects of the MTRR genotype on human status with respect to vitmain B6, plasma folate, homocysteine, and plasma cobalamine levels, modeling, detailed overview
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