Biotin (mine)

biotin is found in what forms

free form and protein-bound form

Free form

biotin

Protein bound

Biocytin

protein bound is also known as what? 

biotinylysine

Biotin is also synthesized by....

intestinal bacteria (only vit that does this (SI))

what do raw egg whites include 

avidin

what does avidin do

irreversibly bind to biotin and prevent absorption

are egg whites always inhibiting biotin?

no, because avidin is heat-labile so when egg white is cooked it no longer affects absorption of biotin

Biotin structure

Ureido ring, Thiophene ring, and valeric acid side chain

structure of biocytin

biotin + lysine

will usually include peptides but they vary; lysine tail is what is always present 

absorption of biocytin (protein-bound) absorption

requires proteolytic digestion (breakdown)

after proteolytic digestion, what occurs in the small intestines 

biocytin or biotinyl peptides are further hydrolyzed into free biotin 

what enzyme is involved hydrozylation in small intestines 

biotinidase (in small intestines)

will biocytin always be digested down to free biotin?

no, it may not be hydrolyzed…

what can occur to undigested biocytin

absorbed and acted on by biotinidase present in plasma or liver, kidney, and adrenal glands

where does biotin absorption mainly occur

upper half of Small intestines (a little in ileum)

how does absorption in upper part of SI occur

via SMVT (small amount by passive diffusion)

Transport across basolateral occurs how?

SMVT but NOT Na dependent

Bacterial synthesized biotin absorbed where...

proximal & mid-segment of colon

Alcohol affect on absorption

inhibits in SI & colon

Activity of biotinidase related to pH

Active over a wide range of pH:

acidic: it cleaves biocytin to produce biotin and lysine

alkaline: it is biotinylated and attaches to biotin (no breakdown but transport)

What type of genetic inheritance is associated with biotinidase deficiency?

Autosomal recessive error of metabolism.

What are some symptoms of biotinidase deficiency in infants?

Developmental delays, dermatitis, alopecia, seizures, acidosis, etc.

What percentage of biotin in plasma is free biotin?

80%

What proteins bind biotin to carry it to tissue sites?

Albumin, globulins, and biotinidase

Where and how much is biotin stored in the body?

In small quantities in muscle, liver, and brain

What is the main influence of the rate and uptake of biotin in cells?

localization of carboxylases 

carboxylases require what (3)

biotin, presence of SMVT, and monocarboxylate transporter 1 (MCT1) 

MCT1

in cells—> because of relationship with carboxylase enzymes —> uniquely puts biotin directly to bind with those carboxylase enzymes (coenzyme role)

what enzymes is biotin associated with?

carboxylases

enzyme roles of Biotin (4- specific enzymes)

• pyruvate carboxylase 

• acetyl-CoA carboxylase 

• propionyl CoA carboxylase

• b-methylcronotyl-CoA carboxylase 

non-coenzyme roles

•Cell proliferation, gene silencing, & DNA repair

•Gene expression & cell signaling

how does biotin attach to carboxylases? what does it result in?

Combines with carboxylase enzymes with the action of holocarboxylase synthetase to form halocarboxylases or biotinylated carboxylases.

in those carboxylases with the biocytin, gets biotinylated to assist in reactions 

what enzyme is used to form halocarboxylases or biotinylated carboxylase

halocarboxylase synthetase

Biotin assist with the addition of what

It assists in the addition of CO2 to substances.

What is the role of biotin in fatty acid synthesis?

It carboxylates acetyl-CoA to form malonyl-CoA for the elongation of a fatty acid chain.

carboxylation of acetyl CoA

acetyl CoA + CO2 —> malonyl CoA = fatty acid synthesis (elongation)

What reaction does biotin facilitate involving pyruvate?

It adds CO2 to pyruvate to yield oxaloacetate.

pyruvate becomes what due to biotin 

pyruvate + Co2 —> OAA 

What amino acid does biotin help break down?

Leucine

Which essential amino acids can be oxidized for energy with the help of biotin?

Isoleucine, threonine, and methionine.

Biotin dependent enzymes (4)

Pyruvate carboxylase

Acetyl-CoA carboxylase

Propionyl-CoA carboxylase

B-methylcrotonyl-CoA carboxylase

Pyruvate decarboxylase role

Converts pyruvate to oxaloacetate

pyruvate decarboxylase function (why it does what it does)

Replenishes oxaloacetate for TCA cycle Necessary for gluconeogenesis

Acetyl-CoA carboxylase does what?

Forms malonyl-CoA from acetate

acetyl CoA + CO2—> Malonyl CoA

Acetyl-CoA carboxylase occurs why?

to commit acetate units to FA synthesis

propionyl-CoA carboxylase does what?

Converts propionyl-CoA to methylmalonyl-CoA

propionyl-CoA carboxylase does its job why?

Provides mechanism for metabolism of some AA and odd-chain FA

B-methylcrotonyl-CoA carboxylase does what?

Converts B- methylcrotonyl-CoA to B-methylglutaconyl-CoA

B-methylcrotonyl-CoA carboxylase does its job why?

Allows catabolism of leucine and certain isoprenoid compounds

remember biotin plays role in leucine catabolism 

Biotin in relation to carboxylase in structure

Byoticyn attaches to carboxylase enzyme through the lysine chain

biotin bound to the lysine residue of carboxylase relation to CO2

will have CO2 attached to biotin portion making it a carrier of activated CO2

CO2 biotin enzyme complex

biotin gains CO2 

how is oxaloacetate made?

pyruvate —> OAA via pyruvate carboxylase

biotin role in synthesis of oxaloacetate (steps, enzyme, co-substrate, biotin’s role)

pyruvate —> OAA 

enzyme: pyruvate carboxylase (biotin is coenzyme)

co-substrate: Mg2+ and ATP 

role: biotin donates CO2

how is biotin involved with propionyl CoA

it aids in coverting it to D-methylmalonyl CoA

what substrates are used to make propionyl CoA

odd chain FA’s and essential amino acids (threonine, methionine, isoleucine, valine)

how is propionyl CoA converted into D-methylmalonyl-CoA

via propionyl CoA carboxylase 

coenzyme: biotin

co-substrate: Mg, ATP

how is biotin involved with leucine

involved in leucine breakdown

what part of leucine breakdown in biotin involved in? 

b-methylcrotonyl CoA —> b-methylglutaconyl CoA 

what is the enzyme that biotin is attached to for leucine breakdown?

b-methylcrotonyl CoA carboxylase

what does biotin do in non-enzyme role? 

Influence cellular function through biotinylation of proteins (non-histone & histone)

(similar to CoA and acetylation)

How does biotin affect histones?

It influences DNA and chromatin structure.

Name a biotin-dependent transcription factor (most important one)

cGMP, nuclear factor (NFKappaB), or tyrosine kinase.

How many genes in humans are dependent on biotin for transcription activity?

Over 2000 genes.

What critical role may biotin play in cellular processes?

It may play a critical role in the cell cycle.

What enzymes break down biotin holocarboxylases?

Proteases

because break at the lysine (amino acid)

What are biotin holocarboxylases catabolized to?

Biotin oligopeptides→ biocytin

remember that biocytin includes biotin and lysine. Lysine may be attached to peptides which is when we have the biotin oligopeptides. 

one we have biocytin, what enzyme acts upon it

Biotinidase

what does biotinidase break biocytin Down to

biotin and lysine 

what happens to the lysine and biotin after breakdown?

excreted via urine, reutilized, or excreted 

What happens to biotin that is synthesized by intestinal bacteria that is not absorbed?

It is excreted in feces

What may the degradation of the vitamin ring structure yield?

Various metabolites

the ureido and thiophene ring

biotin degradation can result in what 2 metabolites

bisnorbiotin and biotin sulfoxide

B-oxidation of side chain in bisnorbiotin produces what

tetranorbiotin

oxidation of sulfur in biotin sulfoxide produces what

Biotin sulfone

What are some food sources of biotin?

Cauliflower, egg yolk, liver, peanuts, cheese

What is a source of biotin synthesis in the body?

Intestinal synthesis of biotin

Is biotin content widely available in foods?

Biotin content is only available for a small number of foods

What is uncertain about synthesized biotin?

Unsure as to bioavailability of synthesized biotin

biotin excretion vs consumption amount 

we excrete more than we consume

What substance inhibits the absorption of biotin?

Avidin inhibits absorption

AI

adult & preg: 30ug

lactation: 35ug

overestimate the amount needed

no UL

Who is at Risk For Deficiency?

rare

high raw egg white intake

biotinidase deficiency

anticonvulsant drug use

IBD

S/S of deficiency

skin rash

hair loss

convulsion

neurological dz

impaired growth in children

What are the most commonly assessed samples for nutritional assessment?

Blood and urine concentrations

what is not not representative of diet or storage

plasma levels 

What indicates a deficiency in biotin?

Decreased urine concentration of biotin and increased excretion of 3-hydroxyisovaleric acid