Tyrosine
-Non essential: as it is synthesized in body from phenylalanine:
BH4
(PAH)
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
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).
dopaquinone
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 decarboxylase
Serotonin is a neurotransmitter, vasoconstrictor. Regulate mood and sleeping.
Its deficiency lead to depression. It is used as antidepressant
Research 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
-
↓↓
1) N-acetylation
2) O-methylation
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 antioxidant
It has important role in protecting skin from damaging effect of UV radiation:
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