Riboflavin (B2) Flashcards
riboflavin is not an __, it does not have a __ function
riboflavin is not an active molecule, it does not have a biological function
riboflavin is a precursor of __ and __
riboflavin is a precursor of FMN and FAD
riboflavin in the form of __ is a __ in many rxns
riboflavin in the form of FAD is a coenzyme in many rxns
most enzymes use __ (75%) rather than __ (25%) and bind the cofactor covalently
most enzymes use FAD (75%) rather than FMN (25%) and bind the cofactor covalently
flavin groups transfer __ or __
flavin groups transfer electrons or protons
most flavin in our body is bound to
oxidoreductase enzymes
more than 90% of flavin-dependent enzymes are __
most use __ rather than __
more than 90% of flavin-dependent enzymes are oxidoreductases
most use FAD rather than FMN
food form of riboflavin
dairy
grains
meat, eggs
vegetables
high protein!
riboflavin is unstable with __ and __
riboflavin is unstable with light exposure and alkaline conditions (baking soda)
transporter of riboflavin
RFVT 1, 2, and 3
__ transporters uptake and excrete riboflavin
3 RFVT transporters uptake and excrete riboflavin
circulation of riboflavin is mostly attached to __ (mainly __)
circulation of riboflavin is mostly attached to proteins (mainly albumin)
dietary form
flavoprotein
which transporter has high affinity for riboflavin?
RFVT3
RFVT 1 and 2 __ riboflavin
RFVT 3 __ riboflavin to __
RFVT 1 and 2 uptake riboflavin
RFVT 3 send riboflavin to urine
immunoglobulins vs albumin
which has higher affinity?
which is main transporter?
immunoglobulins have higher affinity
BUT there is more albumin, so it is the main transporter
absorption, transport, and excretion
- dietary flavoprotein –> FAD (proteases)
- FAD –> FMN (pyrophosphatase)
- FMN –> riboflavin (phosphatase)
- RFVT3 on apical surface brings free riboflavin into cell
- free riboflavin enters blood through RFVT1+2 OR riboflavin in cell becomes FAD/FMN and is used by cell
- in portal blood, riboflavin binds immunoglobulins and albumin
- RBC uptake riboflavin
- remaining to liver and other cells
main riboflavin transporter?
albumin
95% of flavin intake is absorbed, at this point, plasma levels __ and absorption __
95% of flavin intake is absorbed, at this point, plasma levels peak and absorption plateaues
over-excess riboflavin excreted via
feces
4 factors that interfere with digestion and absorption of flavins
- alcohol consumption
- metals: copper, zinc, iron
- caffeine
- vitamins, nicotinamide, ascorbic acid
how does alcohol interrupt flavins
destroys vitamin transporters
metabolism of riboflavin in tissue (3 steps)
riboflavin –> FMN –> FAD
__ hormones impact expression and action of riboflavin enzymes
thyroid hormones impact expression and action of riboflavin enzymes
RFT1
expressed mostly in placenta, intestine, kidney
low transport activity
RFT2
expressed in most tissues, highest in brain, salivary glands, intestine, and colon
RFT2 is highly active with (3)
riboflavin, FAD, FMN
RFT2 is inhibited by
chlorpromazine (anti-psychotic drug)
RFT3
expressed in intestine, prostate, testis, stomach, pancreas
RFT3 is highly homogenous with
RFT1
riboflavin is found in most tissues mainly
liver kidneys and heart
riboflavin is secreted in
milk
almost all riboflavin in tissues is __
almost all riboflavin in tissues is enzyme bound
body stores enough riboflavin for
2-6 weeks
unbound flavins are rapidly __ to __ riboflavin which __ from cell
unbound flavins are rapidly hydrolyzed to free riboflavin which diffuses from cell
intracellular phosphorylation of riboflavin is a way to
trap riboflavin and maintain homeostasis
FMN and FAD are used in 2 types of rxns
- REDOX
- lipid and drug metabolism
FAD has a role in __ to donate __
FAD has a role in ETC to donate electrons
assessment of flavin status
erythrocyte glutathione reductase activity coeffiency (EGRAC) ratio
why use glutathione reductase to measure flavin activity
it uses riboflavin as a cofactor
groups at risk for riboflavin deficiency
- schoolchildren: low intake of milk and meat
- elderly
- athletes: vigorous exercise