biotin and pantothenic acid Flashcards
study reminder
be able to recognize biotin structure on an exam
what is free-biotin called
what is protein-bound biotin called
- biotin
- biocytin
biotin and raw egg diet
avidin binds biotin tightly, causing a deficiency leading to symptoms
biotin is bound to ____ in foods
protein
what is the name of the enzyme that cleaves biocytin to biotin plus lysine
biotinidase
where does the cleavage and absorption of biotin occur?
intestine
what inhibits biotin absorption
avidin
what are the metabolic functions or biotin
- functions as part of coenzyme for carboxylases
- serves as CO2 donor to substrates
- CO2 fixation reactions
- 4 unique enzymes that depend on biotin..all involved in macronutrient and energy metabolism
list the 4 biotin dependent enzymes
- pyruvate carboxylase
- acetyl CoA carboxylase
- propionyl CoA carboxylase
- 3-methylcrotonyl CoA carboxylase
see OH for pathways
these all end in carboxylase so only need to remember first part
what is the biotin dependent enzyme pyruvate carboxylase used in
- glucose metabolism
- important step for gluconeogenesis
- regenerates OAA for gluconeogenesis
what is the biotin dependent enzyme acetyl CoA carboxylase used for
FA synthesis
what is the biotin dependent enzyme propionyl CoA carboxylase used for
-source of energy; entry into TCA
what is the biotin dependent enzyme 3-methlycrotonyl used for
-AA metabolism; leucine degradation
what is the general term used to describe biotin-dependent enzymes
holocarboxylase
with all co-enzymes, there must be attachment to the enzyme. What is needed to attach biotin to the lysine residue of the enzyme
holocarboxylase synthase
once biotin is attached to the enzyme, the enzyme is classified as a holocarboxylase
how could a biotin deficiency occur
- decreased intake
- -> TPN solutions without biotin: bypass the gut and go right into blood
- dec absorption (Avidib)
- deficiency in key enzymes (genetic defects)
egg white injury disease
once biotin-avidin complex forms, it is irreversible, and excreted in feces, preventing absorption
this causes deficiencies in animals (depression hallucinations, muscle pain, dermatitis)
what happens to avidin when it is cooked
it is denatured and the affinity for biotin is therefore destroyed
what are symptoms of biotin deficiency
neurological problems (depression, lethargy, hallucinations, paresthesia of extremeties)
thinning of hair
rash
holocarboxylase synthase
attaches biotin to lysine of caboxylase enzymes
holocarboxylase synthase deficiency
in children=immunodeficiency diseases
biochemical results of biotin deficiency
- dec in biotin-dependent enzymes
- dec gluconeogenesis
- inc pyruvate and lactate
- less glucose produced
- dec Acetyl CoA carboxylase
- build up of acetyl CoA…risk of ketosis
- impaired serum lipids
biotin food sources
- liver
- whole grain cereals
- nuts legumes, peanut butter
- low in fruits and vegetables
bacterial synthesis of biotin
biotin can be synthesized by intestinal bacteria
what affects biotin requirement
- large amounts of raw egg white
- biotinidase deficiency (genetic)
- drug interactions, anticonvulsants, biotin depletion
- pregnancy
what are the two major coenzymes of pantothenic acid
Coenzyme A (CoA)
Acyl Carrier Protein (ACP)
both contains SH (thiol) group, which is where the actions of reactions happens
what is CoA synthesized from
pantothenic acid
cysteine
ATP
metabolic role of CoA
- transfer of Acetyl groups (2C)
- connect to SH groups
- central nutrient metbolism
- many anabolic and catabolic fates
list 5 examples of CoA transferring acetyl groups
- oxidative carboxylation
- pyruvate–>acetyl CoA
- FA oxidation
- complete degradation of acetyl CoA
- ketone body formation
- other carboxylic reactions
- AA catabolism - synthetic reactions
- cholesterol synthesis
Acyl carrier protein (ACP)
another coenzyme form of pantothenic acid, also has a reactive SH group from cysteine
metabolic role of ACP (acyl carrier protein)
- FA synthesis
- is an enzyme complex
- pantothenic acid is a prosthetic group of ACP
- ACP serves as chaperone for FA synthesis
Pantothenic acid deficiency
rare (since it is widespread in food)
- ->pant=greek for every/all
- burning feet syndrome!*
what is burning feed syndrome and what deficiency is it caused by
pain in toes and soles of feet
common in:
WWII prisoners of war
poorly nourished in the Far East
what other uses does pantothenic acid serve
wound treatment
-oral and topical (in rate)
cholesterol-lowering
