Retinol binding proteins

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Retinol-binding proteins (plasma), human.

Retinol-binding proteins (RBP) are transport proteins in the blood plasma and in the cytosol of vertebrate cells . They bind to free vitamin A ( retinol , retinal , retinoic acids ) and thus prevent the uncontrolled effects of these molecules. They also facilitate the transport of lipophilic molecules through the lipophobic cell interior and the blood. In humans there are at least four RBPs and two proteins that are specific for retinoic acid ( CRABP ). Mutations in RBP4 - gene can RBP deficiency with symptoms of vitamin A hypovitaminosis lead.

All RBPs consist of about 135 amino acids , with CRBP I and II being 56% identical in sequence. The four proteins have different tasks and are therefore distributed differently in the different body cells. RBPs are closely related to the lipocalins .

RBP1 (CRBP I)

The CRBP I promotes the conversion of retinol to retinylaldehyde or retinoic acid. It is mainly found in the pigment epithelial cells of the eye or the Kupffer stellate cells of the liver .

RBP2 (CRBP II)

CRBP II is required for the absorption of retinoids from the intestinal lumen and is found exclusively in the enterocytes of the small intestine .

CRABP

The exact function of the retinoic acid binding proteins CRABP I and CRABP II has not yet been clearly clarified. What is certain is that CRABP I lowers the retinoic acid level in the cell, while CRABP II forms a complex with retinoic acid and transports it into the cell nucleus. The CRABP I is present in most body cells, the CRABP II, however, mainly in skin cells .

Individual evidence

  1. ↑ a b Blomhoff R, Green MH, Berg T, Norum KR: transportation and storage of vitamin A . In: Science . 250, No. 4979, October 1990, pp. 399-404. PMID 2218545 .
  2. ↑ Retinol-binding proteins.  In: Online Mendelian Inheritance in Man . (English)
  3. ↑ Napoli JL: Retinoic acid biosynthesis and metabolism . In: FASEB J . . 10, No. 9, July 1996, pp. 993-1001. PMID 8801182 .
  4. ↑ Fogh K, Voorhees JJ, Aström A: Expression, purification, and binding properties of human cellular retinoic acid-binding protein type I and type II . (PDF) In: Arch. Biochem. Biophys. . 300, No. 2, February 1993, pp. 751-5. doi : 10.1006 / fig . 1993.1104 . PMID 8382035 .

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