synthesis: what are the group of compounds that possess the biological activity of all trans retinol
- all-trans retinol
- retinal
- retinoic acid
source: what form is vit a mostly found in
retinyl esters (retinyl palmitate)
requires the presence of _____ to be absorbed
bile salts and phospholipids
what 2 protein carries are needed at the brush border for absorption
- fatty acid binding proteins
2. fatty acid transport proteins
what three components are needed for metabolism of vit a inside the enterocyte
- albumin retinoic acid complex (to liver)
- CRBP II (cellular retinol binding protein II)
- LRAT (lecithin retinol acyl transferase)
what two enzymes are present in vit a
- retinal reductase (retinal -> retinol)
2. retinal oxidase (retinal -> retinoic acid)
metabolic pathway to liver: stored inside hepatic stellate cells
hypervitaminosis A occurs when stellate cells are full
metabolic pathway to liver: attached to _____ and released by exocytosis from the liver
retinol binding porteins (RBP)
metabolic pathway to liver: oxidized to ____ and enters the nucleus
retinoic acid
metabolic pathway to liver: conjugation with _______ for excretion in the bile
glucuronic acid (kiss of death)
what triggers metabolism in the liver cells
CRBP I - cellular retinol binding proteins I
where are the two cellular retinol binding proteins
- CRBP I - all tissues
2. CRBP II - small intestine
what is the rate limiting step for retinoic acid production
retinol dehydrogenase
adds glucuronic acid to both retinol and retinoic acid
glucuronidase
visual cycle: cellular retinol binding protein
CRBP
visual cycle: lecithin retinol acyl transferase
LRAT
visual cycle: cellular retinal binding protein
CRALBP
visual cycle: ______ dehydrogenase
11 - cis retinol
visual cycle: interphotoreceptor retinol binding protein
IRBP
visual cycle: ____ dehydrogenase
all-trans retinal
retinoic acid response promotor regions are activated by
RAR and RXR
all retinoic acid acts as ______ when in the presence of all-trans or 9-cis-retinoic acid
activators
all retinoic acid acts as _____ when in the absence of retinoic acid
repressors
cAMP dependent protein kinase activity ____ after exposure to retinoic acid
increases
retinoylation of proteins by retinoyl CoA (3):
- esterification to serine, theoinine, and tyrosine
- thio-ester to cysteine
- amide to lysine and arginine
retinoic acid increased synthesis of ______ (protein that makes gap junctions)
connexin 43
lack of gap junctions (connexin 43) can lead to
uncontrolled cell growth (cancer)
name 6 happenings of vit a deficiency
- proliferation of immature undifferentiated cells
- decreased apoptosis of cancer cells (decreased caspase 9 and BCL2)
- inactivation of tumor suppressor genes by RXR
- ethanol is a competitive inhibitor of retinol dehydrogenase
- night blindness may be first symptom
- microcytic anemia
vit a can treat acne and psoriasis
T
vit a can enhance macrophage and neutrophil ability to migrate to site of infection
T
antigen presenting cells may help carry out immune system functions of vit a
T
what mg dose would enhance hemoglobin concentrations, decrease the prevalence of anemia, and improve the phagocytic activity of neutrophils
60mg
what dose can increase the risk of birth defects in pregnant women
15,000 IU (teratogenic effect)