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Thread: Vitamin D metabolism pathways

  1. #1
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    Vitamin D metabolism pathways

    Hello fellows!

    while reading some cientific review on endocrine disrupters i came across some intresting informations about the vitamin d3 metabolism.

    you guys can find the whole paper here:
    http://www.oecd.org/officialdocument...doclanguage=en

    and this is the info i would like to share:

    "Vitamin D is an ancient molecule that is found in animals, plants, and zooplankton. While vitamin D is ubiquitous among organisms, VDR is only found in vertebrates.570 VDR and vitamin D signaling
    likely originated with stem vertebrates, as a functional VDR has been identified in the sea lamprey
    (Petromyzon marinus), a basal vertebrate lacking a calcified skeleton.571; 572 Comparisons of vertebrate
    VDR protein sequences demonstrate a high degree of conservation across species, suggesting that the
    vitamin D endocrine axis may be highly conserved throughout vertebrate evolution.573 In humans and
    rodents, 36 tissues express VDR, including tissues that are not associated with the classic vitamin D
    effects of calcium mobilization and ion homeostasis.569 In fact, recent investigation of VDR function
    suggests that VDR signaling has additional non-calcemic roles, including roles in immune system
    function, cell proliferation, and neurodevelopment"

    "Synthesis
    225. All vertebrates possess the vitamin D endocrine axis.574 Aquatic vertebrates obtain vitamin D
    solely from the diet, while terrestrial vertebrates can obtain vitamin D from both the diet and from the
    photolytic conversion of 7-dehydrocholesterol to pre-vitamin D3 in the skin. 7-dehydrocholesterol is
    present in large quantities in the skin of higher vertebrates and is a precursor molecule in the cholesterol
    biosynthesis pathway.569; 575 7-dehydrocholesterol absorbs UVB light in the 290315 nm wavelength,
    which breaks the bond between carbons 9 and 10, creating pre-vitamin D3. Pre-vitamin D3 is
    thermodynamically unstable and rapidly isomerizes to vitamin D3. 568; 576 This photochemical reaction
    does not involve any enzymes and is related to the amount of UVB exposure an individual receives.
    Factors such as latitude, sunscreen use, ethnicity, age, and nutritional status can affect vitamin D3
    production in the skin.577 Vitamin D3 is not biologically active and must be metabolized to its active form
    through two hydroxylation reactions.
    226. The first hydroxylation reaction takes place in the liver. Vitamin D3 is transported from the skin
    bound to transport proteins in the bloodstream. Most vitamin D3 is bound to vitamin D binding protein
    (VDBP), but some is also bound to albumin.568; 578 Once in the liver, the P450 enzyme 25-hydroxylase
    (CYP2R1) adds a hydroxyl group to carbon 25, creating 25-hydroxyvitamin D3. Several P450 enzymes
    have been shown to hydroxylate vitamin D on carbon 25, but only CYP2R1 is highly expressed in the
    liver, and mutations in CYP2R1 are linked to low vitamin D levels and rickets. 568; 579-581 Mutations in
    other candidate P450s do not alter 25-hydroxyvitamin D3 levels. This hydroxylation step is not well
    regulated and is dependent on vitamin D3 substrate availability. Because this reaction reflects the vitamin
    D3 status of an individual, measuring serum levels of 25-hydroxyvitamin D3 is a common method of
    determining the vitamin D status of patients.56

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    the last part of the text was in a bad formatation so i coudnt copy so a pic will do

    i hope you guys find the information usefull

  2. #2
    Snr Moderator dimzel's Avatar
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    Thank you very much. Very interesting information.
    My name is Irina. Sorry my mistakes in English.

  3. #3
    Super Moderator lucysfriend's Avatar
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    That is why some people get SAD in the winter they do not go out into the suns rays. Seasonal affective disorder.
    Phillip and E get that but I do not.
    Just because you have an animal that isn't dead yet, doesn't mean you know how to care for it.

  4. #4
    Snr Moderator dimzel's Avatar
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    A good topic to remember.
    My name is Irina. Sorry my mistakes in English.

  5. #5
    Administrator coolmoon's Avatar
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    This is very good information.
    Saving the world, one reptile at a time. They make me want to be a better person. My name is Ann.

  6. #6
    Snr Moderator dimzel's Avatar
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    It's amazing how difficult and delicate the process is in the organisms of living beings.
    My name is Irina. Sorry my mistakes in English.

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