Tyrosine

-Non essential: as it is synthesized in body from phenylalanine:

(PAH) BH4

BH4= tetrahydrobioptrine . It is the cofactor for all aromatic amino acid hydroxylases ( i.e cofactor for phenylalanine hydroxylase, tyrosine hydroxylase and tryptophan hydroxylase).

- Tyrosine is mixed glucogenic and ketogenic as it gives

fumarate ( so, glucogenic) and acetoacetate (so ketogenic)

-NB: Phenyl alanine is essential amino acid, not synthesized in

body.

-Phenyl alanine is mixed glucogenic and ketogenic as it is

converted into tyrosine which is mixed.

Functions of tyrosine: tyrosine enter in the synthesis of:

1- catecholamines

2- melanin pigment

3- thyroid hormones

1- Catecholamines: dopamine, epinephrine and nor epinephrine

Epinephrine and nor epinephrine are secreted from adrenal medulla

in response to fear, stress, anger, low blood glucose and

hypotension. They stimulate degradation of glycogen and TAG

(stimlate glycogenolysis and lipolysis).

Synthesis of catecholamines

also called tyrosinase

dopaquinone

2-Synthesis of melanin:Melanin is aromatic quinone. It is black or brown pigment present in skin, hair and eyes. Its function is to protect underlying cells from the harmful effects of sun light ( UV radiation).

Albinism: Genetic disease due to

genetic deficiency of tyrosinase

enzyme and lack of melanin synthesis.

This leads to hypopigmentation of skin,

hair and eyes making the albino are

sensitive to sun light (photophobia),

increasing the incidence of skin burns

and cancer.

3- Synthesis of thyroid hormones (T3 and T4):

- Tyrosine +I2 gives monoiodotyrosine (MIT) and diiodotyrosine (DIT) - one MIT + one DIT gives T3 - 2 DIT gives T4 (structures not required)

Tryptophan amino acid- Essential amino acid

- Both glucogenic and ketogenic (gives pyruvate and Acetyl CoA).

Functions:1- Synthesis of serotonin (5-hydroxy tryptamine) in gut, CNS, platelets

(BH4)

THB= BH4 (tetrahydrobioptrine)AAAO= aromatic amino acid decarboxylaseSerotonin is a neurotransmitter, vasoconstrictor. Regulate mood and sleeping.Its deficiency lead to depression. It is used as antidepressantResearch found that fruits (like dates, banana and papaya), turkey, peanuts, almonds, green leaves increase the synthesis of serotonin

Serotonin is popularly thought to be a contributor to feelings of well-being and happiness.

Approximately 90% of the human body's total serotonin is

located in the intestine, where it is used to regulate intestinal

movements. The remainder is synthesized in neurons of the

CNS, where it has various functions. These include the

regulation of mood, appetite, and sleep. Serotonin also has some

cognitive functions, including memory and learning. Increasing

serotonin is the mechanism of action of several classes of

antidepressants.

2- Synthesis of melatonin:

Melatonin is N-acetyl 5-methoxy tryptamine

-

Synthesis and secretion of melatonin is regulated by dark/light cycle. Production of melatonin by the pineal gland in brain is inhibited by light and stimulated by darkness. For this reason melatonin has been called "the hormone of darkness. - Melatonin is sleep-inducing molecule -So ingestion of food rich in tryptophan leads to sleepiness. It is powerful antioxidantIt has important role in protecting skin from damaging effect of UV radiation:

↓ ↓ 1) N-acetylation

2) O-methylation

3- Synthesis of nicotinic acid (niacin)

- Niacin (vitamin B3) is a member of vitamin B complex.-Coenzyme NAD and NADP are derived from niacin.

NAD (to remember the structure, not required)

- Deficiency of niacin leads to pellagra (dermatitis, diarrhea and Dementia). Insomnia and high sensitivity to sunlight.

- Pellagra occurs in case of deficiency of dietary tryptophan which converted into niacin

- Pellagra occurs in areas where people eat mainly maize (corn, the only grain low in digestible niacin)

- 4-Indole and skatole:

- are volatile oils derived from tryptophan metabolism in normal conditions and give stool its characteristic odor.

skatole