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27 Cards in this Set
- Front
- Back
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absorption
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two intestinal transporters: (1) hTHTR-1 apical and basolateral membrane (2) hTHTR-2 apical membrane
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thiamin responsive megaloblastic anemia
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autosomal recessive (rare), megaloblastic anemia, deafness, and diabetes - due to mutation in hTHTR-1. plasma thiamin levels normal. responsive to high levels of thiamin
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thiamin pyrophosphokinase
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enzyme that catalyzes the transfer of PPi from ATP to thiamin
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phosphatase
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removes PPi from thiamin pyrophosphate
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body cells where thiamin high
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liver, heart, kidney, and brain
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excretion
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mainly as thiamin in urine
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reactions
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cleavage of C-C bond of substrate, transfer of one cleavage product to acceptor. substrate always a 2-keto compound.
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types of rxns
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oxidative decarboxylation and transketolations
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oxidative decarboxylation
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pyruvate dehydrogenase (pyruvate to A-coA); alpha-ketoglutarate dehydrogenase (a-ketoglutarate to succinyl-CoA)
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branch chain alph-keto acid dehydrogenase
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(step after deamination)
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ylid
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a neutral molecule with a positive and negative charge on adjacent atoms
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why ylid good?
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allows thiamin to react with electropositive C-2 of substrate
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pyruvate dehydrogenase
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pyruvate (less CO2) binds to thiamin, fragment bound to thiamin transferred to lipoic acid, fragment then transferred to CoA-SH = pyruvate to A-CoA
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formation of ylid
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substrate binding to enzyme causes glutamate to move close to N-1 of pyrimidine ring, pulls electron through ring making N-4 more basic, basic N-4 removes proton from C-2 of thiazole ring
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summary of ylid formation
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(1) TPP protonated when bound to enzyme (2) binding of enzyme to substrate causes rapid deprotonation (3) ylid form of thiamin reacts w/ substrate (4) after release of product, TPP reprotonated
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transketolation
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cleavage of C-C bond of 2-keto sugars. catalyzes transfer of 2C unit from donor ketose to acceptor aldose
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PPP
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reducing power (NADPH); supply ribose-5-p for synthesis of nucleic acid; glycolytic intermediates
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transketolase
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rate limiting enzyme in PPP; thiamin bound to TK less tightly than other thiamin enzymes; first see deficiency in PPP
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deficiency
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Beri-beri: anorexia with weight loss; neurological symptoms, cardiovascular and respiratory symptoms,
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dry beriberi
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(neurotic) lower CHO diet and low energy intake; wasting of tissues; peripheral neuritis (foot and wrist drop)
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wet beriberi
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higher CHO intake and physical activity. cardiovascular and respiratory symptoms predominate - swelling of heart, tachycardia, edema of extremities
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thiamin deficiency in domesticated animals
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retracted head in sheep and chicks
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Wernicke-Korsakoff Syndrome
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acute deficiency associated with high energy intake usually seen in alcoholics. alcohol reduces thiamin absorption. CNS impairment. confused.
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assessment of status
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measure erythrocyte transketolase activity w/ and w/o addition of TPP. > 15% = marginal deficiency; > 25% = clinical deficiency
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toxicity
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relatively non-toxic
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sources
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pork, whole grains, legumes
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RDA
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males: 1.2mg/d
females: 1.1mg/d pregnant/lactating: 1.4mg/d |
