MTR encodes methionine synthase (5-methyltetrahydrofolate-homocysteine methyltransferase; EC 2.1.1.13), the cytosolic, methylcobalamin (vitamin B12)-dependent enzyme that catalyses the remethylation of homocysteine to methionine: (6S)-5-methyltetrahydrofolate + L-homocysteine -> (6S)-tetrahydrofolate + L-methionine. This single reaction links the folate cycle (regenerating tetrahydrofolate from 5-methyltetrahydrofolate) with the methionine cycle (regenerating methionine, and hence S-adenosylmethionine for cellular methylation). It is one of only two cobalamin-dependent enzymes in humans. The enzyme is modular, with a homocysteine-binding domain carrying a catalytic zinc ion that activates the homocysteine thiol, a pterin-binding domain that binds 5-methyltetrahydrofolate, two cobalamin-binding domains that hold the methylcobalamin cofactor, and a C-terminal S-adenosylmethionine-binding activation domain. Catalysis proceeds by shuttling the methyl group through the enzyme-bound cobalamin, which cycles between methylcob(III)alamin and cob(I)alamin. The reactive cob(I)alamin is periodically oxidised to inactive cob(II)alamin and must be reductively reactivated; methionine synthase reductase (MTRR) provides this reactivation and also acts as a chaperone promoting cobalamin loading of the apoenzyme. In the cytosol, cobalamin is handed to methionine synthase within a multiprotein complex that also includes MTRR, MMACHC and MMADHC. Loss-of-function mutations cause cblG homocystinuria with megaloblastic anemia, hyperhomocysteinemia and hypomethioninemia.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005829 cytosol | IBA GO_REF:0000033 | ACCEPT | Summary: Methionine synthase is a cytosolic enzyme. This phylogenetic (IBA) cytosol annotation is consistent with the experimentally supported subcellular localization and with the cytosolic multiprotein cobalamin-processing complex it forms with MTRR, MMACHC and MMADHC. Reason: Cytosol is the correct and precise compartment for the enzyme's catalytic activity. UniProt lists the subcellular location as cytoplasm, and the human cobalamin-processing complex operates in the cytosol. Supporting Evidence: PMID:27771510 the processing of Cbl in cytoplasm occurs in a multiprotein complex composed of at least MS, MSR, MMACHC and MMADHC file:human/MTR/MTR-uniprot.txt SUBCELLULAR LOCATION: Cytoplasm |
| GO:0071265 L-methionine biosynthetic process | IBA GO_REF:0000033 | ACCEPT | Summary: MTR catalyses the terminal, committed step producing L-methionine from L-homocysteine, so participation in L-methionine biosynthesis is a core biological role. This IBA annotation is directly supported by experimental characterization of the human enzyme. Reason: The de novo/remethylation route to methionine (MetH route) is a defined UniPathway step catalysed solely by MTR; this is a central function. Supporting Evidence: PMID:8968737 Methionine synthase catalyzes the remethylation of homocysteine to methionine in a methylcobalamin-dependent reaction file:human/MTR/MTR-uniprot.txt L-methionine biosynthesis via de novo |
| GO:0046653 tetrahydrofolate metabolic process | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: The MTR reaction consumes 5-methyltetrahydrofolate and regenerates tetrahydrofolate, coupling the methionine cycle to the folate cycle. MTR is therefore a genuine participant in tetrahydrofolate metabolism, although this facet is downstream of its methyltransferase activity. Reason: The tetrahydrofolate metabolic aspect is a correct consequence of the catalysed reaction (THF is a product), but it describes a metabolic context rather than MTR's core molecular role, which is captured by methionine synthase activity and methionine biosynthesis. Supporting Evidence: file:human/MTR/MTR-uniprot.txt Reaction=(6S)-5-methyl-5,6,7,8-tetrahydrofolate + L-homocysteine = |
| GO:0008705 methionine synthase activity | IBA GO_REF:0000033 | ACCEPT | Summary: Methionine synthase activity (EC 2.1.1.13) is the defining molecular function of MTR and is supported by phylogenetic, experimental and structural evidence. This is the core molecular function. Reason: Directly corresponds to the enzyme's catalytic activity, well supported at protein level and consistent across IBA, IDA, EXP, IEA and TAS annotations. Supporting Evidence: PMID:17288554 catalyses the conversion of homocysteine to methionine by methyl group transfer |
| GO:0005737 cytoplasm | IEA GO_REF:0000044 | KEEP AS NON CORE | Summary: Cytoplasm is the UniProt subcellular-location-derived compartment for MTR. It is correct but is the less precise parent of the cytosol annotation. Reason: Correct localization but superseded in specificity by the cytosol (GO:0005829) annotation; retain as a broader, non-core localization statement. Supporting Evidence: file:human/MTR/MTR-uniprot.txt SUBCELLULAR LOCATION: Cytoplasm |
| GO:0008270 zinc ion binding | IEA GO_REF:0000002 | ACCEPT | Summary: MTR binds one catalytic zinc ion per subunit in its homocysteine-binding domain (Zn ligated by Cys/His at positions 260, 323 and 324); the zinc activates the homocysteine thiol for methyl transfer. This InterPro IEA is correct and functionally meaningful. Reason: Zinc binding is an experimentally/structurally grounded catalytic cofactor requirement (UniProt COFACTOR Zn(2+); explicit Zn BINDING sites), not a spurious metal annotation. Supporting Evidence: file:human/MTR/MTR-uniprot.txt Note=Binds 1 zinc ion per subunit. |
| GO:0008705 methionine synthase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Automated multi-method IEA (ARBA/InterPro/RHEA/EC 2.1.1.13) assignment of methionine synthase activity, redundant with and consistent with the experimental and IBA support for this molecular function. Reason: Correct core molecular function inferred from family membership, EC and RHEA mappings that match the experimentally verified activity. Supporting Evidence: file:human/MTR/MTR-uniprot.txt EC=2.1.1.13 |
| GO:0031419 cobalamin binding | IEA GO_REF:0000002 | ACCEPT | Summary: MTR binds methylcob(III)alamin as its essential catalytic cofactor via its B12-binding domains (multiple methylcobalamin BINDING residues, including the axial cobalt coordination). This InterPro IEA captures a core cofactor-binding function. Reason: Cobalamin binding is central to the enzyme mechanism (the methyl group is shuttled through enzyme-bound cobalamin); supported by UniProt cofactor and binding-site annotations. Supporting Evidence: file:human/MTR/MTR-uniprot.txt Name=methylcob(III)alamin; Xref=ChEBI:CHEBI:28115; |
| GO:0042558 pteridine-containing compound metabolic process | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: The folate substrate (5-methyltetrahydrofolate) and product (tetrahydrofolate) are pteridine-containing compounds, so this InterPro IEA is true but very broad and non-core. Reason: Correct as a parent metabolic context (folate/THF is a pteridine derivative), but too general to represent the core function; the tetrahydrofolate metabolic process annotation is the more specific parent already captured. Supporting Evidence: file:human/MTR/MTR-uniprot.txt Reaction=(6S)-5-methyl-5,6,7,8-tetrahydrofolate + L-homocysteine = |
| GO:0046872 metal ion binding | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: Generic metal ion binding, subsumed by the more specific and accurate zinc ion binding annotation (MTR's catalytic Zn2+). Retained as a broad, non-informative parent term. Reason: Correct but uninformative; zinc ion binding (GO:0008270) is the specific, preferred molecular function. Cobalt is also present (in cobalamin) but is captured by cobalamin binding. Supporting Evidence: file:human/MTR/MTR-uniprot.txt Name=Zn(2+); Xref=ChEBI:CHEBI:29105; |
| GO:0071267 L-methionine salvage | IEA GO_REF:0000108 | MARK AS OVER ANNOTATED | Summary: This IEA is an inter-ontology logical inference from methionine synthase activity (GO:0008705). L-methionine salvage refers to the methionine salvage (Yang) cycle that regenerates methionine from 5'-methylthioadenosine; MTR instead performs de novo remethylation of homocysteine, which is a distinct route. The inference is over-broad for MTR's biology. Reason: The logically inferred salvage annotation conflates two different routes to methionine. MTR is the de novo homocysteine-remethylation (MetH) step, not a component of the methylthioadenosine-based methionine salvage pathway; better captured by L-methionine biosynthetic process. Supporting Evidence: file:human/MTR/MTR-uniprot.txt L-methionine biosynthesis via de novo |
| GO:0005515 protein binding | IPI PMID:23825108 Interaction between methionine synthase isoforms and MMACHC:... | MARK AS OVER ANNOTATED | Summary: IntAct IPI recording a physical interaction between MTR and MMACHC (Q9Y4U1). The interaction is real and biologically meaningful (part of the cytosolic cobalamin-processing complex), but the bare "protein binding" term is uninformative about MTR's molecular function. Reason: Per curation policy, an experimental IPI is retained rather than removed, but "protein binding" is too generic to convey function. The MTR-MMACHC interaction is better represented by the complex-assembly / cobalamin-processing context. Supporting Evidence: PMID:23825108 the interaction of MS with MMACHC may play a role in the regulation of the cellular processing of Cbls that is required for Cbl cofactor synthesis |
| GO:0009235 cobalamin metabolic process | IEA GO_REF:0000107 | ACCEPT | Summary: MTR is a cobalamin-dependent enzyme that both uses and cycles its cobalamin cofactor and, per biochemical evidence, is the only source of methylcobalamin in mammalian cells; it participates in cobalamin metabolism within the cytosolic Cbl-processing complex. Reason: Correct participation in cobalamin metabolic process, supported by biochemical characterization of methylcobalamin generation and the Cbl-shuttling complex. Supporting Evidence: PMID:16769880 we believe that MS itself is the only source of MeCbl in mammalian cells |
| GO:0031103 axon regeneration | IEA GO_REF:0000107 | MARK AS OVER ANNOTATED | Summary: Electronic transfer (Ensembl Compara) from a rat ortholog. There is no human experimental support that methionine synthase acts directly in axon regeneration; this is a peripheral, weakly supported process attribution. Reason: Over-propagated ortholog-based process annotation not reflecting MTR's core metabolic role; any neuronal relevance is indirect (via methionine/SAM and methylation homeostasis) rather than a direct axon-regeneration function. Supporting Evidence: file:human/MTR/MTR-uniprot.txt FUNCTION: Catalyzes the transfer of a methyl group from |
| GO:0048678 response to axon injury | IEA GO_REF:0000107 | MARK AS OVER ANNOTATED | Summary: Electronic transfer (Ensembl Compara) from a rat ortholog. Not supported by human experimental evidence for a direct role in the response to axon injury. Reason: Over-propagated ortholog-based process annotation; MTR's documented function is the folate/cobalamin-dependent remethylation of homocysteine, not a direct axon-injury response. Supporting Evidence: file:human/MTR/MTR-uniprot.txt FUNCTION: Catalyzes the transfer of a methyl group from |
| GO:0071265 L-methionine biosynthetic process | IEA GO_REF:0000107 | ACCEPT | Summary: Electronic (Ensembl Compara) transfer of L-methionine biosynthetic process, redundant with and consistent with the experimentally supported IBA/IMP annotations to the same term. Reason: Correct core biological process; matches the experimentally validated role of MTR in producing methionine from homocysteine. Supporting Evidence: file:human/MTR/MTR-uniprot.txt L-methionine biosynthesis via de novo |
| GO:0071732 cellular response to nitric oxide | IEA GO_REF:0000107 | MARK AS OVER ANNOTATED | Summary: Electronic transfer (Ensembl Compara) from a rat ortholog. Methionine synthase cobalamin can be inactivated by nitric oxide, giving some rationale, but a direct human "cellular response to nitric oxide" role is not experimentally established here and is peripheral. Reason: Over-propagated ortholog-based process annotation; while cob(I)alamin is chemically NO-sensitive, this term overstates a dedicated NO-response function for MTR relative to its core metabolic role. Supporting Evidence: file:human/MTR/MTR-uniprot.txt Under aerobic |
| GO:0000096 sulfur amino acid metabolic process | TAS Reactome:R-HSA-1614635 | KEEP AS NON CORE | Summary: Homocysteine and methionine are sulfur amino acids, and the MTR reaction is part of sulfur amino acid metabolism. This Reactome TAS is correct but is a broad parent process. Reason: True but general; the more specific L-methionine biosynthetic process and homocysteine metabolic process better capture MTR's core role. Supporting Evidence: PMID:8968737 Methionine synthase catalyzes the remethylation of homocysteine to methionine in a methylcobalamin-dependent reaction |
| GO:0009235 cobalamin metabolic process | TAS Reactome:R-HSA-9759218 | ACCEPT | Summary: Reactome TAS placing MTR in cobalamin (Cbl) metabolism, consistent with its cobalamin-dependent mechanism and role in the cytosolic Cbl-processing complex. Reason: Correct participation in cobalamin metabolic process; MTR both consumes and regenerates its cobalamin cofactor and generates methylcobalamin. Supporting Evidence: PMID:16769880 we believe that MS itself is the only source of MeCbl in mammalian cells |
| GO:0032259 methylation | TAS Reactome:R-HSA-156581 | KEEP AS NON CORE | Summary: MTR is a methyltransferase (transfers a methyl group from methylcobalamin/ 5-methyltetrahydrofolate to homocysteine), so participation in methylation is correct but is a very broad process term. Reason: True but general; the specific molecular function (methionine synthase activity) and the methionine/homocysteine process terms are more informative. Supporting Evidence: PMID:17288554 catalyses the conversion of homocysteine to methionine by methyl group transfer |
| GO:0008705 methionine synthase activity | TAS Reactome:R-HSA-174374 | ACCEPT | Summary: Reactome TAS for methionine synthase activity, describing the half reaction in which the methyl group of methylcobalamin is transferred to homocysteine. Core molecular function. Reason: Correct core molecular function, redundant with the IDA/EXP/IBA/IEA support. Supporting Evidence: PMID:17288554 catalyses the conversion of homocysteine to methionine by methyl group transfer |
| GO:0008705 methionine synthase activity | TAS Reactome:R-HSA-3149539 | ACCEPT | Summary: Reactome TAS for methionine synthase activity, describing the half reaction in which cob(I)alamin is re-methylated by 5-methyltetrahydrofolate. Core molecular function. Reason: Correct core molecular function; complementary half-reaction of the same catalytic cycle. Supporting Evidence: PMID:17288554 catalyses the conversion of homocysteine to methionine by methyl group transfer |
| GO:0008705 methionine synthase activity | EXP PMID:17288554 Crystal structure and solution characterization of the activ... | ACCEPT | Summary: Experimental annotation of methionine synthase activity based on structural and solution characterization of the human enzyme's activation domain in the context of the catalytic homocysteine->methionine methyl-transfer reaction. Reason: Directly supports the core molecular function with experimental evidence on the human protein. Supporting Evidence: PMID:17288554 Human methionine synthase (hMS) is a multidomain cobalamin-dependent enzyme that catalyses the conversion of homocysteine to methionine by methyl group transfer |
| GO:0005515 protein binding | IPI PMID:27771510 Methionine synthase and methionine synthase reductase intera... | MARK AS OVER ANNOTATED | Summary: IPI recording physical interactions of MTR with MMADHC (Q9H3L0), MTRR (Q9UBK8) and MMACHC (Q9Y4U1), placing MTR in the cytosolic cobalamin-processing interactome. The interactions are real and functionally relevant, but the bare "protein binding" term is uninformative. Reason: Per curation policy the experimental IPI is retained rather than removed, but "protein binding" does not convey MTR's molecular function; the assembly into the MTR-MTRR-MMACHC-MMADHC complex is the biologically meaningful description. Supporting Evidence: PMID:27771510 we also observed novel interactions for MSR with MMACHC and with MMADHC and MS with MMADHC |
| GO:0005515 protein binding | IPI PMID:17288554 Crystal structure and solution characterization of the activ... | MARK AS OVER ANNOTATED | Summary: IPI recording interaction of MTR with MTRR (Q9UBK8); the activation domain of human methionine synthase interacts with the FMN-binding domain of MTRR, an interaction enhanced by S-adenosylmethionine. Real and functionally important (reductive reactivation), but the bare term is uninformative. Reason: Experimental IPI retained rather than removed, but "protein binding" is too generic; the MTR activation-domain / MTRR FMN-domain interaction underpins reductive reactivation of the cobalamin cofactor. Supporting Evidence: PMID:17288554 Fluorescence studies show that human activation domain interacts with the FMN-binding domain of human methionine synthase reductase (hMSR) |
| GO:0031103 axon regeneration | ISS GO_REF:0000024 | MARK AS OVER ANNOTATED | Summary: Curator sequence-similarity (ISS) transfer from a rat ortholog. As with the IEA counterpart, there is no human experimental support for a direct role of methionine synthase in axon regeneration. Reason: Ortholog-based process transfer that does not reflect MTR's documented core metabolic function; any neuronal effect is indirect via methionine/SAM homeostasis. Supporting Evidence: file:human/MTR/MTR-uniprot.txt FUNCTION: Catalyzes the transfer of a methyl group from |
| GO:0048678 response to axon injury | ISS GO_REF:0000024 | MARK AS OVER ANNOTATED | Summary: Curator sequence-similarity (ISS) transfer from a rat ortholog; not supported by human experimental evidence for a direct response-to-axon-injury role. Reason: Ortholog-based process transfer not reflecting MTR's core function. Supporting Evidence: file:human/MTR/MTR-uniprot.txt FUNCTION: Catalyzes the transfer of a methyl group from |
| GO:0071732 cellular response to nitric oxide | ISS GO_REF:0000024 | MARK AS OVER ANNOTATED | Summary: Curator sequence-similarity (ISS) transfer from a rat ortholog. Although methionine synthase cobalamin is chemically sensitive to nitric oxide, a dedicated human NO-response function is not experimentally established and is peripheral to the core catalytic role. Reason: Ortholog-based process transfer that overstates a dedicated NO-response role; MTR's core function is folate/cobalamin-dependent homocysteine remethylation. Supporting Evidence: file:human/MTR/MTR-uniprot.txt Under aerobic |
| GO:0008705 methionine synthase activity | IMP PMID:23825108 Interaction between methionine synthase isoforms and MMACHC:... | ACCEPT | Summary: IMP annotation of methionine synthase activity: cblG mutations in MTR decrease the cobalamin-dependent conversion, and cblG-variant cells expressing only a truncated MTR isoform have undetectable methionine synthase activity, tying the activity to the gene. Reason: Loss of MTR function (mutation) abolishing methionine synthase activity provides genetic support for the core molecular function. Supporting Evidence: PMID:23825108 In cblG, mutations in methionine synthase (MTR) decrease conversion of hydroxocobalamin |
| GO:0009235 cobalamin metabolic process | IMP PMID:23825108 Interaction between methionine synthase isoforms and MMACHC:... | ACCEPT | Summary: IMP annotation to cobalamin metabolic process: cblG mutations in MTR decrease the conversion of hydroxocobalamin to methylcobalamin, demonstrating MTR's role in cellular cobalamin processing. Reason: Genetic (mutation) evidence that MTR function is required for normal cobalamin (methylcobalamin) handling supports participation in cobalamin metabolism. Supporting Evidence: PMID:23825108 In cblG, mutations in methionine synthase (MTR) decrease conversion of hydroxocobalamin |
| GO:0071265 L-methionine biosynthetic process | IMP PMID:23825108 Interaction between methionine synthase isoforms and MMACHC:... | ACCEPT | Summary: IMP annotation to L-methionine biosynthetic process: MTR mutations in cblG impair the homocysteine-to-methionine remethylation, linking the gene to methionine biosynthesis by mutant phenotype. Reason: Genetic loss-of-function evidence supporting the core biological process of methionine biosynthesis. Supporting Evidence: PMID:23825108 In cblG, mutations in methionine synthase (MTR) decrease conversion of hydroxocobalamin |
| GO:0005829 cytosol | TAS Reactome:R-HSA-3321918 | ACCEPT | Summary: Reactome TAS localizing MTR to the cytosol (in the context of a defective-MTR reaction). Consistent with the established cytosolic localization. Reason: Correct, specific cytosolic localization. Supporting Evidence: file:human/MTR/MTR-uniprot.txt SUBCELLULAR LOCATION: Cytoplasm |
| GO:0005829 cytosol | TAS Reactome:R-HSA-3322140 | ACCEPT | Summary: Reactome TAS localizing MTR to the cytosol (defective-MTR reaction context). Consistent with the established cytosolic localization. Reason: Correct, specific cytosolic localization. Supporting Evidence: file:human/MTR/MTR-uniprot.txt SUBCELLULAR LOCATION: Cytoplasm |
| GO:0008705 methionine synthase activity | IDA PMID:16769880 Human methionine synthase reductase is a molecular chaperone... | ACCEPT | Summary: IDA for methionine synthase activity: recombinant purified human MS was shown to be an active EC 2.1.1.13 enzyme whose sustained activity requires MSR. This is direct experimental support for the core molecular function. Reason: Direct assay of purified human methionine synthase activity; strongest evidence class for the core molecular function. Supporting Evidence: PMID:16769880 Sustained activity of mammalian methionine synthase (MS) requires MS reductase |
| GO:0005829 cytosol | TAS Reactome:R-HSA-174374 | ACCEPT | Summary: Reactome TAS localizing MTR to the cytosol (methyl-transfer half reaction). Consistent with established cytosolic localization. Reason: Correct, specific cytosolic localization. Supporting Evidence: file:human/MTR/MTR-uniprot.txt SUBCELLULAR LOCATION: Cytoplasm |
| GO:0005829 cytosol | TAS Reactome:R-HSA-3149518 | ACCEPT | Summary: Reactome TAS localizing MTR to the cytosol (MTRR reductive-reactivation reaction context). Consistent with established cytosolic localization. Reason: Correct, specific cytosolic localization. Supporting Evidence: file:human/MTR/MTR-uniprot.txt SUBCELLULAR LOCATION: Cytoplasm |
| GO:0005829 cytosol | TAS Reactome:R-HSA-3149539 | ACCEPT | Summary: Reactome TAS localizing MTR to the cytosol (cob(I)alamin re-methylation half reaction). Consistent with established cytosolic localization. Reason: Correct, specific cytosolic localization. Supporting Evidence: file:human/MTR/MTR-uniprot.txt SUBCELLULAR LOCATION: Cytoplasm |
| GO:0005829 cytosol | TAS Reactome:R-HSA-3204318 | ACCEPT | Summary: Reactome TAS localizing MTR to the cytosol (cobalamin transfer from MMACHC:MMADHC complex to MTRR:MTR). Consistent with established cytosolic localization and the cytosolic Cbl-processing complex. Reason: Correct, specific cytosolic localization. Supporting Evidence: PMID:27771510 the processing of Cbl in cytoplasm occurs in a multiprotein complex composed of at least MS, MSR, MMACHC and MMADHC |
| GO:0005829 cytosol | TAS Reactome:R-HSA-3318563 | ACCEPT | Summary: Reactome TAS localizing MTR to the cytosol (defective-MTRR reaction context). Consistent with established cytosolic localization. Reason: Correct, specific cytosolic localization. Supporting Evidence: file:human/MTR/MTR-uniprot.txt SUBCELLULAR LOCATION: Cytoplasm |
| GO:0007399 nervous system development | TAS PMID:8968737 Human methionine synthase: cDNA cloning and identification o... | MARK AS OVER ANNOTATED | Summary: Legacy TAS to nervous system development citing the MTR cloning/cblG-mutation paper. That paper reports cloning and disease mutations and the neurological phenotype of deficiency, but does not establish a direct developmental role for MTR; the neurological consequences arise from impaired methionine/SAM and folate metabolism. Reason: Over-broad process attribution. The cited paper does not demonstrate MTR acting directly in nervous system development; developmental delay in cblG is a downstream consequence of the metabolic defect rather than a direct developmental function. Supporting Evidence: PMID:8968737 Methionine synthase catalyzes the remethylation of homocysteine to methionine in a methylcobalamin-dependent reaction |
| GO:0050667 homocysteine metabolic process | IMP PMID:23825108 Interaction between methionine synthase isoforms and MMACHC:... | NEW | Summary: MTR directly consumes L-homocysteine, remethylating it to L-methionine, so it is a central participant in homocysteine metabolism. This term is not present in the current GOA set but is well supported and captures a core biological process of the gene (loss of MTR function causes homocystinuria). Reason: Proposed new annotation. Homocysteine metabolic process is a specific, informative process term directly reflecting MTR's substrate; its clinical hallmark on loss of function is homocystinuria/hyperhomocysteinemia. Added to reflect the core_functions homocysteine-metabolism role. Supporting Evidence: PMID:8968737 Methionine synthase catalyzes the remethylation of homocysteine to methionine in a methylcobalamin-dependent reaction PMID:23825108 In cblG, mutations in methionine synthase (MTR) decrease conversion of hydroxocobalamin |
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