Component

Human transcobalamin-cobalamin complex

Human TCN2 carrying cobalamin (holo-TC); distinct from its measured serum concentration.

5 recorded relationships. Experimental role, claim status and evidence remain attached to each record.

Read recorded mechanisms Open recursive mind map

How nutrients influence it

Every nutrient with a recorded effect on this component, credited to the nutrient that acted rather than the chapter that recorded it. Open a nutrient to see the findings and the conditions they were measured under.

How nutrients reach it in more than one step

Chains of two or more recorded steps that end here, grouped by the nutrient they start from. Each step is a separate finding, so a chain is a route a mechanism could take, not proof that it does.

Tracing routes…

What it does

Every recorded relationship this component is part of, grouped by its role. Plain wording comes first; the technical statement follows.

Recorded relationships

What acts on it

  1. Purified human placental receptor and recombinant CD320 extracellular domain bound transcobalamin-cobalamin; high-affinity binding did not require the cytoplasmic domain or membrane orientation.

    Human transcobalamin receptor / CD320 → Human transcobalamin-cobalamin complex source_derived_draftungraded
    Experimental context and source evidence
    cross_nutrient
    false
    experimental_model
    Human placental protein purification and recombinant receptor-domain analysis
    exposure
    Holo-TC binding to native or recombinant CD320
    limitations
    Binding-domain result does not show the cytoplasmic tail is dispensable for endocytosis.
    nutrient_topic
    Vitamin B12 research collection; topical membership is not evidence of a direct dietary effect. · Vitamin B12 (cobalamins)
    organism
    Homo sapiens
    plain_language
    The outside portion of CD320 recognizes B12-loaded transcobalamin.
    primary_references
    [quadros-2009-cd320] The protein and the gene encoding the receptor for the cellular uptake of transcobalamin-bound cobalamin. (2009). https://pubmed.ncbi.nlm.nih.gov/18779389/ DOI: 10.1182/blood-2008-05-158949
    tissue_or_cell_type
    Placental plasma membrane/extracellular receptor domain

    Vitamin B12: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 361–372

    AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Human placental protein purification and recombinant receptor-domain analysis · source_derived_draft · unverified_draft

    ### b12-abs-cd320-holo-binding Purified human placental receptor and recombinant CD320 extracellular domain bound transcobalamin-cobalamin; high-affinity binding did not require the cytoplasmic domain or membrane orientation. Condition category: normal nutrient_topic: Vitamin B12 research collection; topical membership is not evidence of a direct dietary effect. plain_language: The outside portion of CD320 recognizes B12-loaded transcobalamin. organism: Homo sapiens tissue_or_cell_type: Placental plasma membrane/extracellular receptor domain experimental_model: Human placental protein purification and recombinant receptor-domain analysis limitations: Binding-domain result does not show the cytoplasmic tail is dispensable for endocytosis. exposure: Holo-TC binding to native or recombinant CD320 cross_nutrient: false [quadros-2009-cd320] The protein and the gene encoding the receptor for the cellular uptake of transcobalamin-bound cobalamin. (2009). https://pubmed.ncbi.nlm.nih.gov/18779389/ DOI: 10.1182/blood-2008-05-158949
    Complete structured claim and evidence

Where it participates (unsigned role)

  1. In the comparative diabetes study, adding oral calcium after three months of metformin reversed the decline in serum holo-transcobalamin.

    Calcium → Serum holotranscobalamin concentration source_derived_draftungraded
    Experimental context and source evidence
    cross_nutrient
    true
    experimental_model
    21 adults with type 2 diabetes; 14 switched to metformin, then received calcium
    exposure
    Oral calcium after three months of metformin; dose not specified in inspected abstract
    limitations
    Small sequential comparative intervention. Serum holo-TC is an indirect absorption readout and does not directly prove membrane calcium antagonism.
    nutrient_topic
    Vitamin B12 research collection; topical membership is not evidence of a direct dietary effect. · Vitamin B12 (cobalamins)
    organism
    Homo sapiens
    plain_language
    Calcium increased the circulating B12-carrier marker after metformin.
    primary_references
    [bauman-2000-calcium] Increased intake of calcium reverses vitamin B12 malabsorption induced by metformin. (2000). https://pubmed.ncbi.nlm.nih.gov/10977010/ DOI: 10.2337/diacare.23.9.1227
    tissue_or_cell_type
    Circulating holo-transcobalamin

    Vitamin B12: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 439–450

    AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · 21 adults with type 2 diabetes; 14 switched to metformin, then received calcium · source_derived_draft · unverified_draft

    ### b12-abs-bauman-calcium-holotc In the comparative diabetes study, adding oral calcium after three months of metformin reversed the decline in serum holo-transcobalamin. Condition category: normal nutrient_topic: Vitamin B12 research collection; topical membership is not evidence of a direct dietary effect. plain_language: Calcium increased the circulating B12-carrier marker after metformin. organism: Homo sapiens tissue_or_cell_type: Circulating holo-transcobalamin experimental_model: 21 adults with type 2 diabetes; 14 switched to metformin, then received calcium limitations: Small sequential comparative intervention. Serum holo-TC is an indirect absorption readout and does not directly prove membrane calcium antagonism. exposure: Oral calcium after three months of metformin; dose not specified in inspected abstract cross_nutrient: true [bauman-2000-calcium] Increased intake of calcium reverses vitamin B12 malabsorption induced by metformin. (2000). https://pubmed.ncbi.nlm.nih.gov/10977010/ DOI: 10.2337/diacare.23.9.1227
    Complete structured claim and evidence

  2. The human receptor identified as CD320 binds transcobalamin-cobalamin at the plasma membrane and internalizes the carrier-vitamin complex by endocytosis.

    Human transcobalamin receptor / CD320 → Cellular uptake of transcobalamin-bound cobalamin source_derived_draftungraded
    Experimental context and source evidence
    cross_nutrient
    false
    experimental_model
    Human receptor identification and functional characterization
    exposure
    TC-cobalamin complex presented to receptor
    limitations
    No universal uptake rate, tissue sufficiency threshold, or assertion that this is the sole B12 entry route.
    nutrient_topic
    Vitamin B12 research collection; topical membership is not evidence of a direct dietary effect. · Vitamin B12 (cobalamins)
    organism
    Homo sapiens
    plain_language
    CD320 brings carrier-bound B12 into cells.
    primary_references
    [quadros-2009-cd320] The protein and the gene encoding the receptor for the cellular uptake of transcobalamin-bound cobalamin. (2009). https://pubmed.ncbi.nlm.nih.gov/18779389/ DOI: 10.1182/blood-2008-05-158949
    tissue_or_cell_type
    Plasma-membrane endocytosis

    Vitamin B12: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 374–385

    AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Human receptor identification and functional characterization · source_derived_draft · unverified_draft

    ### b12-abs-cd320-cellular-delivery The human receptor identified as CD320 binds transcobalamin-cobalamin at the plasma membrane and internalizes the carrier-vitamin complex by endocytosis. Condition category: normal nutrient_topic: Vitamin B12 research collection; topical membership is not evidence of a direct dietary effect. plain_language: CD320 brings carrier-bound B12 into cells. organism: Homo sapiens tissue_or_cell_type: Plasma-membrane endocytosis experimental_model: Human receptor identification and functional characterization limitations: No universal uptake rate, tissue sufficiency threshold, or assertion that this is the sole B12 entry route. exposure: TC-cobalamin complex presented to receptor cross_nutrient: false [quadros-2009-cd320] The protein and the gene encoding the receptor for the cellular uptake of transcobalamin-bound cobalamin. (2009). https://pubmed.ncbi.nlm.nih.gov/18779389/ DOI: 10.1182/blood-2008-05-158949
    Complete structured claim and evidence

  3. Replacing the missing Glu88 codon by site-directed mutagenesis restored receptor function in the CD320 reconstruction experiments.

    Human transcobalamin receptor / CD320 → Cellular uptake of transcobalamin-bound cobalamin source_derived_draftungraded
    Experimental context and source evidence
    availability_state
    machinery_impairment Imported condition classification; unverified.
    cross_nutrient
    false
    experimental_model
    Reconstruction of human deletion-bearing CD320 followed by codon repair
    exposure
    Insertion of the missing Glu88 codon
    limitations
    Laboratory functional rescue, not a tested treatment in newborns; exact host cell is not specified in the inspected abstract.
    nutrient_topic
    Vitamin B12 research collection; topical membership is not evidence of a direct dietary effect. · Vitamin B12 (cobalamins)
    organism
    Homo sapiens
    plain_language
    Repairing the missing receptor codon restored function in the assay.
    primary_references
    [quadros-2010-e88del] Positive newborn screen for methylmalonic aciduria identifies the first mutation in TCblR/CD320, the gene for cellular uptake of transcobalamin-bound vitamin B(12). (2010). https://pubmed.ncbi.nlm.nih.gov/20524213/ DOI: 10.1002/humu.21297
    tissue_or_cell_type
    Recombinant cellular receptor assay
    trigger_kind
    machinery_impairment Imported condition classification; unverified.

    Vitamin B12: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 400–411

    AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Reconstruction of human deletion-bearing CD320 followed by codon repair · source_derived_draft · unverified_draft

    ### b12-abs-e88del-repair Replacing the missing Glu88 codon by site-directed mutagenesis restored receptor function in the CD320 reconstruction experiments. Condition category: machinery_impairment nutrient_topic: Vitamin B12 research collection; topical membership is not evidence of a direct dietary effect. plain_language: Repairing the missing receptor codon restored function in the assay. organism: Homo sapiens tissue_or_cell_type: Recombinant cellular receptor assay experimental_model: Reconstruction of human deletion-bearing CD320 followed by codon repair limitations: Laboratory functional rescue, not a tested treatment in newborns; exact host cell is not specified in the inspected abstract. exposure: Insertion of the missing Glu88 codon cross_nutrient: false [quadros-2010-e88del] Positive newborn screen for methylmalonic aciduria identifies the first mutation in TCblR/CD320, the gene for cellular uptake of transcobalamin-bound vitamin B(12). (2010). https://pubmed.ncbi.nlm.nih.gov/20524213/ DOI: 10.1002/humu.21297
    Complete structured claim and evidence

  4. Fibroblasts from five asymptomatic newborns with elevated methylmalonic acid and homozygous CD320 p.Glu88del showed reduced uptake of holo-transcobalamin.

    Human CD320 p.Glu88del variant → Cellular uptake of transcobalamin-bound cobalamin source_derived_draftungraded
    Experimental context and source evidence
    availability_state
    machinery_impairment Imported condition classification; unverified.
    cross_nutrient
    false
    experimental_model
    Five newborn-derived fibroblast lines with homozygous CD320 deletion
    exposure
    Homozygous c.262_264delGAG / p.Glu88del
    limitations
    Asymptomatic neonatal ascertainment does not establish later clinical severity. Cellular uptake does not isolate binding from receptor expression or trafficking.
    nutrient_topic
    Vitamin B12 research collection; topical membership is not evidence of a direct dietary effect. · Vitamin B12 (cobalamins)
    organism
    Homo sapiens
    plain_language
    A receptor deletion reduced B12 delivery in patient cells.
    primary_references
    [quadros-2010-e88del] Positive newborn screen for methylmalonic aciduria identifies the first mutation in TCblR/CD320, the gene for cellular uptake of transcobalamin-bound vitamin B(12). (2010). https://pubmed.ncbi.nlm.nih.gov/20524213/ DOI: 10.1002/humu.21297
    tissue_or_cell_type
    Human cultured fibroblasts
    trigger_kind
    machinery_impairment Imported condition classification; unverified.

    Vitamin B12: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 387–398

    AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Five newborn-derived fibroblast lines with homozygous CD320 deletion · source_derived_draft · unverified_draft

    ### b12-abs-e88del-uptake Fibroblasts from five asymptomatic newborns with elevated methylmalonic acid and homozygous CD320 p.Glu88del showed reduced uptake of holo-transcobalamin. Condition category: machinery_impairment nutrient_topic: Vitamin B12 research collection; topical membership is not evidence of a direct dietary effect. plain_language: A receptor deletion reduced B12 delivery in patient cells. organism: Homo sapiens tissue_or_cell_type: Human cultured fibroblasts experimental_model: Five newborn-derived fibroblast lines with homozygous CD320 deletion limitations: Asymptomatic neonatal ascertainment does not establish later clinical severity. Cellular uptake does not isolate binding from receptor expression or trafficking. exposure: Homozygous c.262_264delGAG / p.Glu88del cross_nutrient: false [quadros-2010-e88del] Positive newborn screen for methylmalonic aciduria identifies the first mutation in TCblR/CD320, the gene for cellular uptake of transcobalamin-bound vitamin B(12). (2010). https://pubmed.ncbi.nlm.nih.gov/20524213/ DOI: 10.1002/humu.21297
    Complete structured claim and evidence

In the sources

Preserved passages that mention this component, quoted exactly. Open one to read it in context.

    This is a research prototype built from draft material. It is not medical advice, and its statements still await verification against the original studies.

    Evidence, AI assistance and curation standards