This document summarizes the metabolism of basic amino acids like histidine, arginine, and lysine. Histidine is metabolically glucogenic and can be converted to histamine. It regulates gastric acid secretion and synthesis of carnosine. Arginine is also glucogenic and can be converted to nitric oxide, which acts as a vasodilator. Lysine is a ketogenic amino acid that can be broken down to acetyl CoA. It is important for collagen and elastin cross-linking. Disorders of lysine metabolism can cause hyperlysinemia and associated issues.

1. METABOLISM OF BASIC
AMINO ACID
By
N. Santhosh Kumar
Asst. Professor
Department of Biochemistry
SIMS&RH, Tumkur

2. Basic, nutritionally semi essential,
metabolically glucogenic a.as
Basic, nutritionally essential,
metabolically Ketogenic a.a

3. Histidine
Basic, nutritionally semi essential,
metabolically Glucogenic a.a’s

5. IMPORTANCE OF HISTIDINE
Histidine Histamine + CO2
Decarboxylase
PLP
Tissue protein
synthesis
It removes heavy metals from the body
Excessive production of histamine causes asthma &
allergic reactions
Regulates HCl secretion by gastric mucosa
Synthesis of Imp Peptides: Carnosine & Anserine
(muscle), ergothionine (RBCs, liver & brain).
Act as protector for nerve cells

6. Transferase
Hydrolase
Mental retardation & defect in
speech

7. Significance of FIGLU
• Excretion of FIGLU provides diagnostic test for folic acid deficiency
• normal less than 30mg/day
Histidine Load Test / FIGLU test
• 5gm of Histidine given.
• Three times at 4 hr intervals & 24hrs urine collected.
• To differentiate the Folate deficiency from Vit B12 def in Megaloblastic
anemia (both Folate & Vit B12 def)
• In the folic acid deficiency (More than 30mg/day excreted in urine )

8. Arginine
Basic, nutritionally semi essential,
metabolically glucogenic a.a’s

9. Synthesis &
Degradation
Of
Arginine

10. Metabolic Fate of
Arginine
1
2
3
4
5
6 7
Stabilizes the collagen triple helix

11. Nitric oxide (NO)
Very short half-life (about 5 seconds).
Nitric Oxide Synthase
Guanidino
Group
NADPH, FMN,
FAD, Heme &
THB.

12. ISO-Enzymes of Nitric Oxide Synthase (NOS)
• 3 isoforms, these are products of 3 different genes and seen in almost
all tissues.
Neuronal NOS Macrophage NOS Endothelial NOS
NOS-1 or nNOS is seen
in central and peripheral
neurons.
-Especially in cerebellum
and gastrointestinal tract
NOS-2 , iNOS seen in
macrophages &
neutrophils.
- Induced by cytokines
(Interleukin-1 and
tumour necrosis factor).
NOS-3 or eNOS is seen
in endothelial cells,
platelets, endocardium
& myocardium
- In these sites, it act as
arterial relaxation.

13. Functions of Nitric
Oxide Act as a vasodilator & causes
relaxation of smooth muscles
Involved in the erectile function of
penis
mediates the bactericidal actions of
macrophages
Neurotransmitter
an inhibitor of platelet aggregation
and adhesion.
Regulates the Blood pressure
mediated through cGMP
& Protein kinase G.

14. Nitric Oxide in Diseases and Treatment
Angina pectoris Pulmonary hypertension:
-Nitroprusside (directly release
NO•) & Nitro-glycerin (requires
glutathione to produce NO•)
Dilute
Coronary arteries
- Inhalation of NO• is useful in the
treatment of pulmonary hypertension and
high altitude pulmonary edema.
- NO• produces pulmonary vasodilatation,
without lowering systemic blood pressure

15. Lysine
Basic, nutritionally essential,
metabolically Ketogenic a.a’s

16. • It contains two amino groups , can undergoes direct transamination
• In Degradation process, it produces intermediates Saccharopine, α-
Ketoadipate, Crotonyl CoA than ultimately generates Acetyl CoA
• Lysine & OH-lysine residues of collagen & elastin are imp in cross
linking
• Precursor of carnithin, which serves to shuttle fatty acyl groups across
mitochondrial membrane

17. Disorders
Periodic hyperlysinemia Persistent hyperlysinemia
Characterized by elevated plasma
lysine & ammonia
Lysine competitively inhibit liver
arginase causes hyperammonemia
leads to ammonia intoxication
Inherited as an autosomal
recessive trait.
Impaired conversion of lysine
toα-KG to saccharopine
Not associated with hyper
ammonemia
Mental retarded (rare conditions)