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Cited by 899Retinoids in leukemia and cellular processesProtein Interaction Studies and Fluorescence AnalysisCholesterol and Lipid Metabolism

Retinol-binding protein: the transport protein for vitamin A in human plasma

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Kanai, Masamitsu, Raz, Amiram, Goodman, DeWitt S.·1968·Journal of Clinical Investigation
DOI 10.1172/jci105889PMC PMC297364
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Abstract

Vitamin A circulates in human plasma as retinol bound to a specific transport protein. This protein differs from the known low and high density plasma lipoproteins and has a hydrated density greater than 1.21. In order to study this protein, volunteers were injected intravenously with retinol-15-(14)C. Plasma was collected 1-3 days later, and the purification of retinol-binding protein (RBP) was monitored by assaying for (14)C and also by following the fluorescence of the protein-bound retinol. Purification of RBP was effected by the sequence: Cohn fractionation, chromatography on columns of Sephadex G-200 and diethylaminoethyl (DEAE)-Sephadex, preparative polyacrylamide gel electrophoresis, and finally chromatography on Sephadex G-100. These procedures resulted in a preparation of RBP which was at least 98% pure and which had been purified more than 1500-fold. Purified RBP has alpha(1) mobility on electrophoresis and has a molecular weight of approximately 21,000-22,000. There appears to be one binding site for retinol per molecule of RBP. Solutions of RBP are fluorescent (characteristic of retinol) and have ultraviolet absorption spectra with peaks at 330 mmu (resulting from the bound retinol) and at 280 mmu. There are no fatty acid or fatty acyl chains present in purified RBP. The usual concentration of RBP in plasma is of the order of 3-4 mg/100 ml. In plasma, RBP apparently circulates as a complex, together with another, larger protein with prealbumin mobility on electrophoresis. The RBP-prealbumin complex remains intact during Cohn fractionation and during chromatography on Sephadex and on DEAE-Sephadex columns. The complex dissociates during gel electrophoresis, permitting the isolation and subsequent purification of each of the components. The complex is again formed by mixing together solutions of the separated RBP and of prealbumin. Retinol transport in plasma thus appears to involve both a lipid-protein (retinol-RBP) interaction and a protein-protein (RBP-prealbumin) interaction.

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Crossref · 10.1172/jci105889

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  • Vitamin A released from hepatic storage sites in Stellate cells by retinyl ester hydrolysis is complexed with RBP4 to form holo-RBP4.

    “When required by the body, vitamin A liberated from its hepatic storage sites in Stellate cells by retinyl ester hydrolysis is complexed with a 21 kDa retinoid-binding protein belonging to the lipocalin family called retinol-binding protein 4 (RBP4) to form holo-RBP4.24”

    From Chemistry of the Retinoid (Visual) Cycle (2014) · cites this paper as [24]

    The Discussion (page not provided) identifies holo-RBP as retinol bound to RBP, and reports an RBP molecular weight of approximately 21–22 kDa. The paper does not establish the claim’s hepatic stellate-cell storage and retinyl ester hydrolysis steps, or identify RBP as RBP4 or a lipocalin. (LLM, conf=0.88)

    Experimental — accuracy not yet measured

  • In the blood circulation, vitamin A is transported in the form of all-trans-retinol bound to RBP4.

    “In the blood circulation, it is transported in the form of all-trans-retinol bound to a 21 kDa carrier plasma retinol-binding protein 4 (RBP4).”

    From The Role of Vitamin A in Retinal Diseases (2022) · cites this paper as [36]

    The Discussion (page not available in our copy) states that retinol circulates in plasma bound to retinol-binding protein and gives its molecular weight as approximately 21,000–22,000. The paper does not specify that the circulating retinol is the all-trans isomer. (LLM, conf=0.85)

    Experimental — accuracy not yet measured

  • To prevent loss of the low molecular weight RBP4 through renal filtration, holo-RBP4 forms a complex with transthyretin (TTR).

    “To prevent loss of the low molecular weight RBP4 through renal filtration, holo-RBP4 forms a complex with a 55 kDa transthyretin (TTR), that is also known for transporting thyroxine [35,36,37].”

    From The Role of Vitamin A in Retinal Diseases (2022) · cites this paper as [36]

    The Discussion says the RBP–prealbumin complex prevents filtration of the small RBP molecule and its loss in urine; it tentatively identifies that prealbumin with the thyroxine-binding protein. The full citing sentence’s 55 kDa figure is not supported by this copy, which instead reports molecular weights of 61,000 and 73,000 for prealbumin. (LLM, conf=0.86)

    Experimental — accuracy not yet measured

  • Holo-RBP4 circulates in plasma in complex with transthyretin, which prevents its urinary excretion by increasing molecular weight.

    “Holo-RBP4 circulates in the plasma in complex with a second protein called transthyretin, which by increasing the molecular weight of the overall complex prevents holo-RBP4 from being excreted in the urine.24,496”

    From Chemistry of the Retinoid (Visual) Cycle (2014) · cites this paper as [24]

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Cites

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Research works printed but not linked: 1

  1. Raz, A., M. Kanai, and DeW. S. Goodman. 1968. Retinol binding protein (RBP): a newly-recognized plasma lipoprotein. Federation Proc. 27: 594. (Abstr.)

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Authors
Kanai, M., Raz, A., & Goodman, D. S.
Affiliations
  • Shinshu University (JP)
  • Columbia University (US)
Venue
Journal of Clinical Investigation
Publisher
American Society for Clinical Investigation
Published
1968-09-01
Volume
47
Issue
9
Pages
2025-2044
ISSN
0021-9738 (ISSN-L)
DOI
10.1172/jci105889
PMC
PMC297364
OpenAlex
W2164579477
Cited by
899
References
41
Citations by year
2026: 8 · 2025: 14 · 2024: 24 · 2023: 12 · 2022: 23 · 2021: 12 · 2020: 16 · 2019: 14 · 2018: 9 · 2017: 16 · 2016: 19 · 2015: 21 · 2014: 22 · 2013: 15 · 2012: 8
FWCI
6.50
Type
journal article
Language
en
Open access
Locations
  • Journal of Clinical Investigation (publishedVersion)
  • PubMed Central (publishedVersion)
  • PubMed (publishedVersion)
Funders
  • Health Research Council of the City of New York
  • National Institutes of Health (5r01am005968-25)
Topics
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Retinoids in leukemia and cellular processes
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Protein Interaction Studies and Fluorescence Analysis
  • Health Sciences › Medicine › Surgery › Cholesterol and Lipid Metabolism
Keywords
retinol-binding protein, vitamin A transport, plasma retinol, prealbumin, protein-protein interaction, protein purification, molecular weight, serum lipoproteins
MeSH terms
Adult, Binding Sites, Biological Transport, Blood Proteins, Carbon Isotopes, Chromatography, Electrophoresis, Humans, Molecular Weight, Spectrum Analysis, Vitamin A

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