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Zinc may be absorbed from diet via zinc transporter mediated pathways, or, when coupled with amino acids, via amino acid transporter pathways. When zinc is coupled with amino acids in diet, it may dissociate from those amino acids in the acidic environment of the stomach prior to entering the small intestine. An experimentally-determined value for any pre-absorptive dissociation of zinc from a zinc amino acid complex (ZnAA) is necessary for the accurate compartmental modeling of zinc metabolism when provided as ZnAA compared with ionic zinc, which we will perform in a future study.
The current study will allow us to determine the dissociation of zinc from ZnAA, while serving as a pilot test of a novel technique to determine for the first time an individual's zinc transport kinetics.
An experimentally-determined value for any pre-absorptive dissociation of zinc from ZnAA is necessary for the accurate compartmental modeling of zinc metabolism when provided as ZnAA compared with zinc chloride, which we will perform in a future study.
The current study will allow us to determine the pre-absorptive dissociation of zinc from ZnAA, while serving as a pilot test of a novel technique to determine for the first time an individual's zinc transport kinetics. Since zinc absorption kinetics follow a saturable process, the zinc transport maximum (Tr_max) and transport rate (K_Tr) can be determined by fitting Hill transport equation to measurements of absorbed zinc at 3 or more levels of zinc intake (mg zinc/d):
Total Absorbed Zinc (TAZ) = (Zinc Intake * Tr_max) / (Zinc Intake + K_Tr)
Although population data have been used to estimate zinc transport kinetics (Tran, et al. AJCN 2004), Tr_max and K_tr have never been determined in individual subjects. We plan to determine the fractional zinc absorption (FZA) from multiple levels of dietary zinc in rapid succession (Chung, et al. AJCN 2004) and, therefore, estimate an individual's transport maximum and rate, Tr_max and K_Tr. Once Tr_max and K_Tr are known, the FZA can be used to determine an unknown zinc intake from zinc chloride and any zinc dissociated from the ZnAA complex using the following equation:
Zinc Intake = (Tr_max / FZA) - K_Tr
Since zinc that dissociates from the ZnAA complex will compete for absorption with the inorganic zinc stable isotopic oral tracer (70-zinc chloride), reducing the amount of that tracer absorbed, we can therefore determine the total zinc intake (the sum of the known zinc in the controlled study diet and the unknown quantity of zinc dissociated from ZnAA pre-absorption) based on the transport kinetics (FZA, Tr_max and KTr).
In other words, for the meal with added ZnAA, the zinc intake is the sum of the zinc in the test meal (3.6 mg zinc and 0.4 mg 70-Zn tracer) and the zinc that dissociates from the ZnAA complex pre-absorption. Since the intact ZnAA (i.e. that zinc that does not dissociate pre-absorption from the ZnAA complex) is absorbed by a different transport mechanism (Sauer, et al. Biometals 2017), it does not compete with the stable isotope tracer for absorption via zinc cation transporters and is, therefore, not part of the "zinc intake" for the purpose of these calculations.
If the hypothesized 20% dissociation is correct (i.e. 3 mg zinc dissociated from an initial 15 mg ZnAA), the total amount of ionic zinc will be 7 mg (the 3.6 mg base diet, 0.4 mg zinc stable isotope tracer, and 3 mg dissociated zinc), and the FZA will therefore be the same as that from a 7 mg test diet (the 3.6 mg base diet, 0.4 mg zinc tracer, and 3 mg zinc as zinc chloride).
Chung CS, Stookey J, Dare D, Welch R, Nguyen TQ, Roehl R, Peerson JM, King JC, Brown KH. Current dietary zinc intake has a greater effect on fractional zinc absorption than does longer term zinc consumption in healthy adult men. Am J Clin Nutr 2008;87(5):1224-9.
Sauer AK, Pfaender S, Hagmeyer S, Tarana L, Mattes AK, Briel F, Kury S, Boeckers TM, Grabrucker AM. Characterization of zinc amino acid complexes for zinc delivery in vitro using Caco-2 cells and enterocytes from hiPSC. Biometals 2017;30(5):643-61.
Tran CD, Miller LV, Krebs NF, Lei S, Hambidge KM. Zinc absorption as a function of the dose of zinc sulfate in aqueous solution. Am J Clin Nutr 2004;80(6):1570-3.
Fractional Zinc Absorption
Zinc amino acid complex
Children's Hospital and Research Center Oakland
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Children's Hospital & Research Center Oakland
Published on BioPortfolio: 2019-05-06T17:20:30-0400
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A ZINC metalloenzyme that catalyzes the transfer of a methyl group from BETAINE to HOMOCYSTEINE to produce dimethylglycine and METHIONINE, respectively. This enzyme is a member of a family of ZINC-dependent METHYLTRANSFERASES that use THIOLS or selenols as methyl acceptors.
Carboxypeptidases that are primarily found the DIGESTIVE SYSTEM that catalyze the release of C-terminal amino acids. Carboxypeptidases A have little or no activity for hydrolysis of C-terminal ASPARTIC ACID; GLUTAMIC ACID; ARGININE; LYSINE; or PROLINE. This enzyme requires ZINC as a cofactor and was formerly listed as EC 18.104.22.168 and EC 22.214.171.124.
A family of zinc finger transcription factors that share homology with Kruppel protein, Drosophila. They contain a highly conserved seven amino acid spacer sequence in between their ZINC FINGER MOTIFS.
A DNA binding protein, transcriptional regulator, and proto-oncogene protein that contains 10 CYS2-HIS2 ZINC FINGERS. It functions as a positive or negative regulator of expression for target genes involved in organism development.
EXOPEPTIDASES which use a metal such as ZINC in the catalytic mechanism.
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