Biotin

Question 1

Where can biotin be synthesized?

Answer 1

• can be synthesized by human intestinal bacteria but still considered an essential micronutrient

Question 2

Explain biotins struture

Answer 2

• bicyclic ring structure
  -BIOTIN (free biotin)
• ureido ring
  *sulfur ring with Valerie acid side chain
• BIOCYTIN (bound to biotin)
• biotin + lysine
• step in proteolysis during biotin digestion

Question 3

Where does biotin bind to its enzymes

Answer 3

• lysine (holocarboxylase)

Question 4

Explain biotin absorption

Answer 4

• bound to proteins in foods
• PROTEASES cleave biocytin from the proteins (biotin + lysine)
• BIOTINIDASE: cleaves biocytin to biotin plus lysine
• free biotin is absorbed

Question 5

Where does biotin absorption occur?

Answer 5

• intestine because it hasn’t been absorbed yet

Question 6

What is the metabolic function of biotin

Answer 6

• functions aspart of coenzyme carboxylase
• serves as CO2 donor to substrates
• FOUR unique enzymes that depend on biotin (all involved in macronutrient and energy metabolism

Question 7

What are the 4 biotin-dependent enzymes

Answer 7

1. Pyruvate carboxylase
2. acetyl CoA carboxylase
3. propionyl CoA carboxylase
4. 3-methylcrotonyl CoA carboxylase

Question 8

Explain pyruvate carboxylase

Answer 8

• glucose metabolism
• important step for gluconeogenesis
• regenerates OAA for TCA cycle

Question 9

Explain acetyl CoA carboxylase

Answer 9

• fatty acid synthesis

Question 10

Explain propionyl CoA carboxylase

Answer 10

• source of energy; entry into TCA

Question 11

Explain 3-methylcrotonyl CoA carboxylase

Answer 11

• amino acid metabolism; leucine degradation

Question 12

What is holocarboxylase

Answer 12

• a general term to describe biotin-dependent enzymes with biotin attached to them
• as with all co-enzymes, there must be an attachment to the enzyme (physical interaction)

Question 13

What is holocaroxylase synthase?

Answer 13

• is needed to attach biotin to the lysine residue of the enzyme

Question 14

When is the enzyme classified as holocarboxylase?

Answer 14

• once biotin is attached to the enzyme

Question 15

What is the egg white injury disease

Answer 15

• historical studies of rats fed raw egg white developed syndrome of dermatitis hair loss and neurological abnormalities called egg white injury disease

Question 16

What is avidin

Answer 16

• is a glycoprotein in egg white that binds biotin very tightly

Question 17

What happens once biotin-avidin complex forms?

Answer 17

• it is irreversible not broken down, excreted in faces
• prevents absorption and causes deficiency

Question 18

What is the solution to not bind avidin to biotin

Answer 18

• avidin can be denatured by cooking so it will not bind to biotin

Question 19

What do studies show about biotin being synthesized by human intestinal bacteria

Answer 19

• studies show that urine and fecal amounts were greater than dietary amounts meaning that there was some other source of biotin

Question 20

what bacterial synthesis of biotin do?

Answer 20

• does not replace need from diet but can contribute to status
• implications for long-term antibiotic use

Question 21

What are the causes of biotin deficiency

Answer 21

• reduced dietary intake
• biotin free TPN (total parental nutrition) over long periods of time
• consumption of raw egg what ever long period of time

Question 22

What are the symptoms of biotin deficiency

Answer 22

• neurological symptoms; depression, lethargy, hallucinations, paresthesia of extremities
• hair, ski and nail problems; thinning of hair, dermatitis, brittle nails

Question 23

are deficiencies rare in biotin?

Answer 23

• yes due to bacterial synthesis

Question 24

What does biotinidase do?

Answer 24

• Biotinidase releases biotin from dietary proteins and recycles biotin from degraded biotin-containing enzymes, ensuring adequate free biotin for absorption and reuse.

Question 25

What would happen if there was a biotinidase deficiency?

Answer 25

1. Cannot absorb biotin from food Dietary biotin is mostly bound to proteins. Without biotinidase, the intestine cannot free biotin → poor absorption. 2. Cannot recycle biotin from old enzymes

Question 26

Why us biotinidase be a serious deficiency

Answer 26

Biotinidase deficiency is serious enough that many countries screen newborns for it, because early treatment prevents symptoms.

Question 27

What is holocarboxylase synthase deficiency

Answer 27

-carboxylase enzymes, leading to multiple carboxylase deficiency even when biotin intake is normal. - rare inborn error of biotin metabolism - deficiency often have immunodeficiency diseases

Question 28

What are the results biochemically of biotin deficiency

Answer 28

- decrease in biotin-dependent enzymes - decerase pyruvate carboxylase - accumulation of biotin substances in the urine (since enzymes not working)

Question 29

What would decrease in pyruvate carboxylase cause?

Answer 29

- decreased gluconeogenesis - increase pyruvate and lactate - less glucose produced

Question 30

what would decrease in acetyl CoA carboxylase (fatty acid synthesis) cause?

Answer 30

- build up of acetyl CoA risk of ketosis - could have an impact on impaired serum lipids

Question 31

How could biotin deficiency occur?

Answer 31

- DECREASED INTAKE: - DECREASED ABSORPTION: - DECREASED UTILIZATION:

Question 32

What does decreased intake mean?

Answer 32

- Not enough in the diet - TPN solutions without biotin

Question 33

What does decreased absorption mean

Answer 33

- deficiency in biotinidase - avidin - medications

Question 34

What does decreased utilization mean?

Answer 34

- deficiency in holocarboxylase synthase

Question 35

What are some biotin food sources

Answer 35

- not a lot of data from food composition tables - liver - whole grain cereals - nuts, legumes, peanut butter - low in fruits and veg

Question 36

What is the biotin requirement?

Answer 36

- Adult AI: 30 ug/day - not enough data for UL - requirement affected by: * large amounts of raw egg white * biotinidase deficiency (genetic) * drug interactions; anticonvulsants; biotin depletion * pregnancy

Question 37

What is TPN and biotin deficiency

Answer 37

- in 1980s a number of patents with malabsorption problems who needed TPN developed signs of biotin deficiency symptoms - the patients biochemistry showed abnormally high blood levels of beta-methycrotonate and beta-hydroxypropionate which is a characteristic of biotin deficiency - treatment w biotin corrected symptoms

Question 38

What happens when biotin is deficient, how does this affect biotin dependent enzymes

Answer 38

- the biotin-dependent enzyme will build up and will show elevated organic acids * LOOK AT BIOTIN PAPER*

Question 39

What are biotin medical pitfalls

Answer 39

- failure to diagnose biotin deficiency promptly - failure to include biotin in TPN solutions - failure to recognize that some anticonvulsants can interfere with with biotin absorption - failure to recognize that long-term use of antibiotics which can lead to biotin deficiency