Vitamin-A-dependent zinc-binding protein and intestinal absorption of Zn in chicks

Abstract

1. It was demonstrated that the development of experimental avitaminosis A in chicks led to secondary zinc deficiency. The balance of Zn in the chick became negative, while the Zn content of various tissues decreased. Thus in vitamin-A-deficient chicks the serum Zn content was 1258 (SD 26.3) μg/l which was considerably lower than 1652 (SD 97.8) μg/l in controls.2. Zn absorption was considerably reduced throughout the entire small intestine of vitamin-A-deficient chicks and most markedly in the ileal region. Within 72 h after retinyl acetate administration Zn absorption was fully restored in this region of the intestine.3. The 65Zn-binding capacity of soluble proteins, present in the supernatant fraction of ileal-mucosa homogenates of vitamin-A-deficient chicks, was found to increase 2.6 times by 72 h after the administration of a single dose of retinyl acetate.4. A vitamin-A-dependent Zn-binding protein (ZnBP), absent in vitamin-A-deficient chicks, was isolated from the ileal mucosa after their repletion with vitamin A. Competitive-binding studies (calcium, cadmium, copper) showed the protein to be highly specific for Zn ions.5. The molecular weight of ZnBP wa5 83 kDa. The association constant of the protein-Zn complex was 0.8 x 106/mol. The protein was acidic with approximately 20% of its amino acid residues belonging to dicarboxylic acids. ZnBP was found to be a glycoprotein, and it contained hexose as a carbohydrate component.6. It is suggested that ZnBP is involved in the binding of Zn in the ileal mucosa of chicks.

High-dose dietary supplementation of vitamin A induces brain-derived neurotrophic factor and nerve growth factor production in mice with simultaneous deficiency of vitamin A and zinc

“…Vitamin A can facilitate Zn absorption via involvement in the synthesis of a protein which binds to Zn at the ileal mucosa. 19 Moreover, it is worthy of note that several studies have shown that the serum retinol concentration is responsive to experimental Zn depletion and repletion. Zn affects many aspects of vitamin A metabolism possibly via involvement in the synthesis of a protein which contributes to inter-and intracellular transport of vitamin A.…”

“…Interestingly, vitamin A supplementation has been known to facilitate Zn absorption. 19 In consideration of these difficulties, the present study was aimed to clarify whether high vitamin A supplementation can improve production of the neurotrophins in such communities.…”

Increased Nerve Growth Factor by Zinc Supplementation with Concurrent Vitamin A Deficiency Does Not Improve Memory Performance in Mice

“…On the other hand, Vit. A is necessary for synthesis of a protein which binds to Zn at the ileal mucosa and facilitates its absorption (29). Taken together, it is speculated that change in the daily intake of one or both nutrients may alter the metabolism of the other.…”

Oxidative stress and innate immunity status in chickens exposed to high dose of ascorbic acid

“…The ice‐cold washed ileum (see above) was cut into 4‐cm segments and used for intestinal preparations. Transport of cadmium or iron through the apical membrane of enterocytes into mucosal cells was estimated by accumulating mucosal preparations (AMPs) . AMPs were incubated at 41 °C for 30 min in 6 ml of one of the following solutions: control buffer (145 mmol·l –1 of NaCl, 4 mmol·l –1 of KCl, 4 mmol·l –1 of Tris‐HCl, 20 mmol·l –1 of fructose, pH 7.4), buffer with 0·05 mmol·l –1 of cadmium (CdCl 2 , Sigma‐Aldrich); buffer with 0·05 mmol·l –1 of L‐AA; buffer with mixture of 0·05 mmol·l –1 of L‐AA and 0·512 mmol·l –1 of iron (AA + Fe1); buffer with mixture of 0·05 mmol·l –1 of L‐AA and 2·56 mmol·l –1 of iron (AA + Fe2).…”

“…Transport of cadmium or iron through the apical membrane of enterocytes into mucosal cells was estimated by accumulating mucosal preparations (AMPs). 12 AMPs were incubated at 41 C for 30 min in 6 ml of one of the following solutions: control buffer (145 mmolÁl -1 of NaCl, 4 mmolÁl -1 of KCl, 4 mmolÁl -1 of Tris-HCl, 20 mmolÁl -1 of fructose, pH 7.4), buffer with 0Á05 mmolÁl -1 of cadmium (CdCl 2 , Sigma-Aldrich); buffer with 0Á05 mmolÁl -1 of L-AA; buffer with mixture of 0Á05 mmolÁl -1 of L-AA and 0Á512 mmolÁl -1 of iron (AA + Fe1); buffer with mixture of 0Á05 mmolÁl -1 of L-AA and 2Á56 mmolÁl -1 of iron (AA + Fe2). After incubation, the concentration of Cd or Fe was estimated in AMP by atomic absorption spectrophotometry using a flame AAS (PerkinElmer, model AAnalyst 700.…”