THIAMINE (VITAMIN B1)RIBOFLAVIN (VITAMIN

B2)

Maryam Jamilah Binti Abdul Hamid082013100002IMS Bangalore

Learning outcome

Student should be able to know the

activity of both vitamins as

coenzyme

Student should be able to list down

the effect of deficiency in both

vitamins.

INTRODUCTIONThiamineSource: Aleurone layer of cerealsDaily requirement: 1-1.5 mg/day

RiboflavinSource: liver,dried yeast,egg,whole

milk,fish,cereals,legumes & green leafy vegetablesDaily requirement: 1.5 mg/day.Pregnant lady, lactation & old age needadditional 0.2-0.4 mg/day

THIAMINE (VITAMIN B1)

1. Pyruvate dehydrogenase› Coenzyme form: Thiamine pyrophosphate

(TPP)› Process: oxidative decarboxylation of

alpha keto acids

Pyruvate Acetyl CoA + CO2

Pyruvate dehydrogenase

TPP

2. Alpha ketoglutarate dehydrogenase› Coenzyme form: Thiamine

pyrophosphate (TPP)› Process: oxidative decarboxylation of

alpha ketoglutarate

Alpha ketoglutarate Succinyl CoA + CO2

Alpha ketoglutarate dehydrogenase

TPP

3. Transketolase› Coenzyme form: Thiamine pyrophosphate

(TPP)› Process: HMP shunt

Ribulose-5-phosphate Glyceraldehyde-3-phosphate

Xylulose-5-phosphate Sedoheptulose-7-phosphate

TransketolaseTPP

Deficiency Manifestations of Thiamine

Beriberi Early symptoms:

Anorexia Dyspepsia Heaviness Weakness

Easily exhausted

Wet Beriberi Cardiovascular

manifestation Edema

Leg Face Trunk Serous cavities

Palpitation Breathlessness Distended neck

veins

Dry Beriberi Central Nervous

System (CNS) manifestation

Difficulty in walking

Peripheral neuritis with sensory disturbance Complete paralysis

Infantile Beriberi

Mother is thiamine deficiency

Restlessness

Sleeplessness

Wernicke-Korsakoff

Syndrome /Cerebral beriberi

Encelopathy(malfunction of the brain) Ophthalmoplegia Nystagmus Cerebellar ataxia

Psychosis

Polyneuritis

Alcohol inhibits intestinal absorption of thiamine Impairment of

conversion of pyruvate to acetyl CoA

Increased plasma con. pyruvate and lactate

Lactic acidosis

Pregnancy

Old age

RIBOFLAVIN (VITAMIN B2)

2 types of coenzyme:-

Flavin mono nucleotide (FMN)

Flavin adenine dinucleotide (FAD)

Enzymes containing riboflavin are called

flavoprotein

FMN-dependent enzyme1. Amino acid oxidation

› FMN is reduced› Reoxidised by molecular O2 to produce H2O2

L-amino acid L-imino acid

FMN FMNH2

H20 + 1/2O2 H2O2 O2Catalase

2. Respiratory chain› Complex I› NADH dehydrogenase complex contain

FMN› e- are transported in the following manner› NAD+ FMN CoQ› FMN collect e- from NADH and pass to Fe-S› NADH + H+ + FMN FMNH2 + NAD+

FAD Accepts Hydrogen

FAD accepts 2H+ and 2e-

FAD + 2H+ FADH2

FAD is reduced.

FAD-dependent enzyme

Succinate fumarate

FAD FADH2

Acyl CoA α-β-unsaturated acyl CoA

FAD FADH2

succcinate dehydrogenase

acyl CoA dehydrogenase

CITRIC ACID

CYCLE

BETA OXIDATION

FAD-dependent enzyme (cont.)

DEGRADATION OF PURINE

NUCLEOTIDE

Riboflavin Deficiency

Uncommon because riboflavin is

synthesized by the intestinal flora but it

is possible !

Usually accompanies other deficiency

diseases:-

› Beriberi (deficiency of thiamine)

› Pellagra (deficiency of niacin)

› Kwashiorkor (protein-energy malnutrition)

Manifestations for Riboflavin Glossitis› inflammation with depapillation of the

dorsal surface of the tongue Magenta colored tongue

Cheilosis› dry scaling of the vermilion surface of the

lips and angles of the mouth

Angular stomatitis› inflammation in the mouth

Circumcorneal vascularization Proliferation of the bulbar

conjunctival capillaries

REFERENCE

Vasudevan, D., S, S., & Vaidyanathan, K. (2013).Textbook of biochemistry for medical students. (7th ed., pp. 477-480). New Delhi: Jaypee Brothers Medical Publishers (P) Ltd.

Thank you