one carbon metabolism (16) Flashcards
what is the precursor for:
dopamine
epi
norepi
tryosine
what is the precursor for:
melanin
thryoxine
all trosine
what is the precursor for:
GABA
histidine
GABA- glutamate
histidine-histamine
what is the rate limiting step in the formation of Dopa?
tyrosine hydroxylation
what cofactor does tyrosine hydroxylase require?
tetrahydrobiopterin
what enzyme degrades catecholamines?
monoamine oxidase (MAO)
what enzyme does the conversion of dopamine to norepi?
dopamine b-hydroxylase
what 2 things does the enzyme dopamine b- hydroxylase require?
ascorbate (vit C) and molecular oxygen
what enzyme is need for norepi methylation to make epinephrine? what compound acts as the methyl donor?
enzyme: phenylethanolamine N methyltransferase
SAM is methyl donor
what is disease is the result of a defect in the melanin producing pathway?
albinism
what vitamin deficiency can result form a deficiency of tryptophan?
niacin deficiency- pellagra
true or false
glutamate decarboxylase is a pyridoxal phosphate dependent enzyme
true
needed to make GABA
what enzyme catalyzes the formation of histidine?
histidine decarboxylase
what does histidine decarboxylase require?
pyridoxal phosphate
list 4 reasons why the body needs single carbon fragments
o Formation of methionine form homocysteine
o Biosynthesis of purines
o Biosynthesis of pyrimidines
o Biosynthesis of glycine from CO2 and NH4+ by glycine synthase
what carrier is able to carry the most oxidized one carbon group? what is “the most oxidized one carbon group”?
biotin carrying CO2
when does THF act as a 1 carbon acceptor?
in degradative reactions
when does THF act as a 1 carbon donor?
in biosynthetic reactions
what precursor is the production of THF depend on?
dietary folate
what part of THF are humans unable to synthesize?
the pterin ring
what form of folate is normally seen in the diet?
polyglutamines with the glutamate moieties attached in y-peptidyl linkages
is folate normally in the oxidized or reduced state before absorption?
oxidized state
what enzyme is used to reduce folic acid to THF?
dihydrogolic acid reductase
what is the name of the THF in the most reduced state?
N-5 methyl THF
what is the name of the THF in the most oxidized state?
N-5 formyl THF
N-5 formino THF
N-5,N-10 methenyl THF
what is the name of the THF in the intermediate state?
N-5,N-10 methylene THF
what is the only reaction to use N5-methyl THF?
for the formation of methionine
what reaction is the main source for making N5, N10-methlene THF
the interconversion of serine and glycine
what are 3 drug classes that can cause folate deficiency?
- oral contraceptives
- barbiturates: impairs absorption & utilization
- methotrexate: antimetabolite used in cancer chemo
what are the two main drugs that are considered “anti folates”?
aminopterin
methotrexate
list 5 important methylation reactions that require SAM
- Norepi→epi
- Guanidinoacetate→creatine
- Acetylserotonin→melatonin
- Phosphatidylethanolamine to phosphatidylcholine
- Methaylation of DNA
what enzyme catalyzes the reaction of the regeneration of methionine from homocysteine?
homocysteine methyltransferase
what 2 cofactors does homocysteine methyltransferase use?
N5 methyl THF
B12
what disease process is elevated levels of homocysteine correlated with?
increased risk of athrosclerosis
vitamin supplementation with what 3 compounds has been shown to reduce the levels of homocysteine?
B12
folate
pyridoxal phosphate
what enzyme catalyzes the reaction:
homocysteine & serine condensing to form cystathionine?
what is the cofactor for this enzyme?
cystathionine synthase
cofactor: pyridoxal phosphate
what disease is caused by a deficiency in the enzyme cystathionine synthase?
homocystinuria
people with homocystinurea have a higher risk of ____ and a lower risk of _____
higher risk of heart attacks
lower risk of colon cancer
what version of cobalmin is seen in the MMAM reaction?
the adenosyl version
what version of cobalamin is seen in teh HMT reaction?
hydroxyl version
what two reactions in the body require cobalamin?
- Conversion of L-methylmalonyl coA to succinyl coA
2. the action of homocysteine methyltransferase
what type of anemia does a deficiency in THF and B12 lead to?
megablastic anemia aka pernicious anemia
what is a B12 deficiency associated with?
demyelination and degeneration of spinal cord
what is usually the cause of a B12 deficiency?
a problem with intrinsic factor in the gut
what is the name of the transporter for B12?
transcobalamine
in the folate trap, what form is THF getting stuck in?
in the N5 methyl form (the most oxidized form)
if a person is in a “folate trap” what does it manifest as?
anemia
