The methylcobalamin metabolism of cultured human fibroblasts

Chu, Richard C.; Begley, James A.; Colligan, Pamela D.; Hall, Charles A.

doi:10.1016/0026-0495(93)90080-8

Cited by 16 publications

(16 citation statements)

References 13 publications

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“…"ROS" formation and lipid peroxidation were prevented by methyl donors methionine, betaine, folic acid and methylcobalamine (Chu et al, 1993;DeLong et al, 2002;Friso and Choi, 2002) (Table 1). However, phenylimidazole, DPI, dicumarol or BCNU did not affect arsenite induced cytotoxicity ( Table 1).…”

Section: Resultsmentioning

confidence: 98%

A comparison of hepatocyte cytotoxic mechanisms for chromate and arsenite

et al. 2005

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Section: Resultsmentioning

confidence: 98%

A comparison of hepatocyte cytotoxic mechanisms for chromate and arsenite

et al. 2005

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“…MeCbl is the predominant form of the cofactor in human plasma [31], and following its entry into cells, it must be dealkylated by the action of CblC to be subsequently partitioned to meet cellular demands for the MeCbl and AdoCbl cofactor forms [19]. While the role of CblD is expected to be downstream of CblC, identification of the cbl D gene did not provide obvious insights into the role of the encoded protein.…”

Section: Discussionmentioning

confidence: 99%

The C-terminal domain of CblD interacts with CblC and influences intracellular cobalamin partitioning

et al. 2013

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Mutations in cobalamin or B12 trafficking genes needed for cofactor assimilation and targeting lead to inborn errors of cobalamin metabolism. The gene corresponding to one of these loci, cblD, affects both the mitochondrial and cytoplasmic pathways for B12 processing. We have demonstrated that fibroblast cell lines from patients with mutations in CblD, can dealkylate exogenously supplied methylcobalamin (MeCbl), an activity catalyzed by the CblC protein, but show imbalanced intracellular partitioning of the cofactor into the MeCbl and 5′-deoxyadenosylcobalamin (AdoCbl) pools. These results confirm that CblD functions downstream of CblC in the cofactor assimilation pathway and that it plays an important role in controlling the traffic of the cofactor between the competing cytoplasmic and mitochondrial routes for MeCbl and AdoCbl synthesis, respectively. In this study, we report the interaction of CblC with four CblD protein variants with variable N-terminal start sites. We demonstrate that a complex between CblC and CblD can be isolated particularly under conditions that permit dealkylation of alkylcobalamin by CblC or in the presence of the corresponding dealkylated and oxidized product, hydroxocobalamin (HOCbl). A weak CblC·CblD complex is also seen in the presence of cyanocobalamin. Formation of the CblC·CblD complex is observed with all four CblD variants tested suggesting that the N-terminal 115 residues missing in the shortest variant are not essential for this interaction. Furthermore, limited proteolysis of the CblD variants indicates the presence of a stable C-terminal domain spanning residues ~116–296. Our results are consistent with an adapter function for CblD, which in complex with CblC·HOCbl, or possibly the less oxidized CblC·cob(II)alamin, partitions the cofactor between AdoCbl and MeCbl assimilation pathways.

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“…Mutations in the genes that encode the enzymes or proteins involved in Cbl processing, trafficking and biosynthesis are defined by Cbl complementation groups ( cblA-cblG and mut ) [ 23 , 24 ]. A study by Chu et al suggested that dietary methylcobalamin (MeCbl) and adenosylcobalamin (AdoCbl) must undergo processing of their upper axial ligand prior to their incorporation into MS and MUT, respectively [ 25 ]. The first case report of functional Cbl deficiency caused by an inborn error of metabolism was provided by Harvey Mudd et al, more than 40 years ago [ 26 ].…”

Section: Cellular Processing Of B 12 : Mmachc (Cblc)mentioning

confidence: 99%

Proteomics of vitamin B12 processing

Hannibal

DiBello

Jacobsen³

2013

Clinical Chemistry and Laboratory Medicine

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The causes of cobalamin (B 12 , Cbl) deficiency are multifactorial. Whether nutritional due to poor dietary intake, or functional due to impairments in absorption or intracellular processing and trafficking events, the major symptoms of Cbl deficiency include megaloblastic anemia, neurological deterioration and in extreme cases, failure to thrive and death. The common biomarkers of Cbl deficiency (hyperhomocysteinemia and methylmalonic acidemia) are extremely valuable diagnostic indicators of the condition, but little is known about the changes that occur at the protein level. A mechanistic explanation bridging the physiological changes associated with functional B 12 deficiency with its intracellular processers and carriers is lacking. In this article, we will cover the effects of B 12 deficiency in a cblC -disrupted background (also referred to as MMACHC) as a model of functional Cbl deficiency. As will be shown, major protein changes involve the cytoskeleton, the neurological system as well as signaling and detoxification pathways. Supplementation of cultured MMACHC-mutant cells with hydroxocobalamin (HOCbl) failed to restore these variants to the normal phenotype, suggesting that a defective Cbl processing pathway produces irreversible changes at the protein level.

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The methylcobalamin metabolism of cultured human fibroblasts

Cited by 16 publications

References 13 publications

A comparison of hepatocyte cytotoxic mechanisms for chromate and arsenite

A comparison of hepatocyte cytotoxic mechanisms for chromate and arsenite

The C-terminal domain of CblD interacts with CblC and influences intracellular cobalamin partitioning

Proteomics of vitamin B12 processing

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