Amino acid and biological peptides for medical students

1. Class 3
Reactions
of
amino acids

2. COOH
HCH3N
+
R
COOH
HH2N
R
C
COO
_
HCH2N
R
Low pH
Acidic
High pH
Basic
Amino acid
Anionic form
Cationic form
Ionization of amino
acids

3. What is Zwitter ion?
What is Amphoteric molecule?
What is Isoelectric pH?

5. Peptide bondsPeptide bonds
 Different types of amino acidsDifferent types of amino acids
undergo polymerization byundergo polymerization by
peptide bond formationpeptide bond formation
 Peptide bonds are importantPeptide bonds are important
part of protein structure.part of protein structure.
 If they are broken orIf they are broken or
hydrolyzed it degradehydrolyzed it degrade
proteinprotein
Amino acids
Dipeptide
Tripeptides
Peptides
Polypeptides
(Proteins)

6. PeptidebondPeptidebond
formationformation
H
H2N
R
C C OH
OII
COOH
H
R
CN
H
H
H
H2N
R
C C
O
II
COOH
H
R
CN
H
HO H

7. PeptidesPeptides
 Composed of small number of amino acidsComposed of small number of amino acids
 Linkage is peptide bondsLinkage is peptide bonds
 Synthesized in bodySynthesized in body
 Have specific functionHave specific function
 Digestion of protein also leadsDigestion of protein also leads

8. Biologically IMP peptidesBiologically IMP peptides

9. Examples and BiomedicalExamples and Biomedical
importanceimportance
 HormoneHormone : Insulin, glucagon, Vasopressin,: Insulin, glucagon, Vasopressin,
OxytocinOxytocin
 AntioxidantAntioxidant : Glutathione: Glutathione
 AntibioticsAntibiotics : Gramicidin S: Gramicidin S
 Anti-tumor drugAnti-tumor drug : Bleomycin: Bleomycin
 Sweetening agentSweetening agent : Aspartame: Aspartame

10. Biologically IMP peptidesBiologically IMP peptides
 TripeptideTripeptide : Glutamic acid, Cysteine and Glycine: Glutamic acid, Cysteine and Glycine
 Reduced form asReduced form as GSHGSH
 Oxidised form asOxidised form as GS-SGGS-SG
 Characterised by Gama peptide bonds,Characterised by Gama peptide bonds,
 not digestednot digested by peptidaseby peptidase
 Found in all cell except nerve cellFound in all cell except nerve cell
 Biological antioxidant, Amino acid absorptionBiological antioxidant, Amino acid absorption
GlutathioneGlutathione

11. Biologically IMP peptidesBiologically IMP peptides
 FunctionsFunctions::
 1.1. CoenzymeCoenzyme in oxidation reduction reactionin oxidation reduction reaction
 2. Maintains Red Cell2. Maintains Red Cell Membrane integrityMembrane integrity
 3.3. Protects HBProtects HB against Oxidationagainst Oxidation
 4. Free radical and peroxide4. Free radical and peroxide scavangingscavanging
 5.5. DetoxicationDetoxication
GlutathioneGlutathione
Hemolytic anemia due to G6PD deficiency

12. InsulinInsulin
 fromfrom ββ cell ofcell of pancreaspancreas
 ContainsContains 30 + 2130 + 21 amino acidsamino acids
 Hypoglycemic HormoneHypoglycemic Hormone
GlucagonGlucagon
 fromfrom αα cell ofcell of pancreaspancreas
 Contains 29 amino acidsContains 29 amino acids
 Hyper glycemic hormoneHyper glycemic hormone

13. AngiotensinAngiotensin
 Angiotensinogen synthesized by liverAngiotensinogen synthesized by liver
 Angiotensinogen to angiotensin I by Renin (10 AAs)Angiotensinogen to angiotensin I by Renin (10 AAs)
 Angiotensin I to II by ACEAngiotensin I to II by ACE (Angiotensin converting enzyme)(Angiotensin converting enzyme)
 Angiotensin II active form Have 8 AAsAngiotensin II active form Have 8 AAs
 Vaso-constructor increase arterial pressureVaso-constructor increase arterial pressure
 Increase synthesis of Aldosteron -Na+ retentionIncrease synthesis of Aldosteron -Na+ retention
 ACE inhibitors used as antihypertensive & CCFACE inhibitors used as antihypertensive & CCF

14. OxytocinOxytocin
 Hormone of posterior pituitaryHormone of posterior pituitary
 ContainsContains 99 amino acidsamino acids
 Stimulates contraction of uterusStimulates contraction of uterus
 Hormone secreted by posterior pituitary
 Contains 9 amino acids
 Decreases GFR and retains body water
 Increases Blood pressure
Vasopressin (ADH)Vasopressin (ADH)

15. CorticotropinCorticotropin
 Hormone of Anterior pituitaryHormone of Anterior pituitary
 ContainsContains 3939 amino acidsamino acids
 Stimulates adrenal cortex for secretion of steroidStimulates adrenal cortex for secretion of steroid
hormoneshormones
TRHTRH
 Hypothalamic hormoneHypothalamic hormone
 ContainsContains 33 amino acidsamino acids
 Stimulates release of thyrotropin from anteriorStimulates release of thyrotropin from anterior
pituitarypituitary

16. GastrinGastrin
 Local hormone from StomachLocal hormone from Stomach
 Stimulates production of gastric juiceStimulates production of gastric juice
SecretinSecretin
 G I PeptideG I Peptide
 Stimulates secretion of pancreatic juiceStimulates secretion of pancreatic juice

17. BradykininBradykinin
 Contains 9 amino acidsContains 9 amino acids
 Formed in bloodFormed in blood
 Power full vasodilatorPower full vasodilator
 Causes contraction of smooth musclesCauses contraction of smooth muscles
 Stimulates pain receptorsStimulates pain receptors
EnkephalinsEnkephalins
 Peptide formed in CNSPeptide formed in CNS
 Binds to certain receptors in brain andBinds to certain receptors in brain and
induces analgesia (Killing pain sensation)induces analgesia (Killing pain sensation)

18. KallidinKallidin
 Contains 10 amino acidsContains 10 amino acids
 Power full vasodilatorPower full vasodilator
AspartameAspartame
 Di-peptide,Di-peptide,
 Neutra sweet, artificial sweetenerNeutra sweet, artificial sweetener
 L aspartyl phenylalanyl methyl esterL aspartyl phenylalanyl methyl ester
 Not suitable for phenylketourics.Not suitable for phenylketourics.

19. Important reactionsImportant reactions
ofof
Amino acidsAmino acids

20. DeaminationDeamination
 Removal of amino groupRemoval of amino group from amino acid byfrom amino acid by
enzyme to forms keto acidenzyme to forms keto acid
 Deamination:1.Deamination:1. OxidativeOxidative deaminationdeamination
2.2. Non oxidativeNon oxidative deaminationdeamination
Glutamate α keto glutarate
NH2
Amino acid deaminase

21. TransaminationTransamination
 Transfer of amino group of one amino acid to aTransfer of amino group of one amino acid to a
keto acidketo acid
 Result in formation of new amino acid and a ketoResult in formation of new amino acid and a keto
acidacid
 Enzymes : Transaminase orEnzymes : Transaminase or
Amino transferaseAmino transferase
 Coenzymes : Pyridoxal phosphateCoenzymes : Pyridoxal phosphate
 Advantage: Non essential amino acid synthesisAdvantage: Non essential amino acid synthesis
 Interconversion of amino acidsInterconversion of amino acids

22. Amino acid
α ketoacid Amino acid
α ketoacid
Amino transferase
Pyridoxal phosphate
General reaction
Alanine
α ketoglutarate
L- Glutamate
Pyruvate
Alanine
transaminase
Pyridoxal phosphate

23. Reaction with ammoniaReaction with ammonia
 Acidic amino acids reacts with NHAcidic amino acids reacts with NH33 to formto form
amide.amide.
 They are part of protein structureThey are part of protein structure
 Serve as source of NitrogenServe as source of Nitrogen
L- Glutamate
L- Glutamine
α keto glutarate
NH3NH3
Enzyme - Glutaminase

24. DesulphurationDesulphuration
 Sulphur containing amino acid during theirSulphur containing amino acid during their
catabolism oxidises sulph-hydryl group to formcatabolism oxidises sulph-hydryl group to form
keto acid.keto acid.
C
COOH
CH2
SH
NH2H
SH2
COOH
CH3
NHC
COOH
CH2
NH2C
COOH
CH3
C O
Cysteine
Desulphurase
Imino acid
Keto acid

25. DecarboxylationDecarboxylation
 Removal of coo group to form aminesRemoval of coo group to form amines
 EnzymesEnzymes : Amino acid decarboxylase: Amino acid decarboxylase
 CoenzymeCoenzyme : Pyridoxal phosphate: Pyridoxal phosphate
GlutamateGlutamate GABAGABA
NeurotransmitterNeurotransmitter
HistidineHistidine HistamineHistamine
Effect on BP, Allergic condEffect on BP, Allergic cond
TyrosineTyrosine TyramineTyramine
Contracts uterusContracts uterus
TryptophanTryptophan TryptamineTryptamine
Serotonin, NTSerotonin, NT
Decarboxylas
e
PLP
CO2

26. Colour reactions of amino acidsColour reactions of amino acids
Biuret reactionBiuret reaction Peptide bondsPeptide bonds
Ninhydrine reactionNinhydrine reaction Free amino groupsFree amino groups
Xanthoproteic reactionXanthoproteic reaction Aromatic amino acidsAromatic amino acids
Millon’s reactionMillon’s reaction TyrosineTyrosine
Hopkins – cole reactionHopkins – cole reaction Tryptophan – indole ringTryptophan – indole ring
Sakaguchi’s reactionSakaguchi’s reaction Arginine – guanidino groupArginine – guanidino group
Nitroprusside reactionNitroprusside reaction Free SH groupFree SH group
Pauly’s reactionPauly’s reaction Histidine – imidazole groupHistidine – imidazole group
Lead acetate reactionLead acetate reaction SH groupSH group

27. Biologically important compounds fromBiologically important compounds from
amino acidsamino acids
GlycineGlycine Heme, Purine base, Bile salt,Heme, Purine base, Bile salt,
GlutathioneGlutathione
Aspartic andAspartic and
Glutamic acidGlutamic acid
Purine, pyrimidine basesPurine, pyrimidine bases
TyrosineTyrosine Thyroxine, Adrenaline, Melaniine,Thyroxine, Adrenaline, Melaniine,
TryptamineTryptamine
TryptophaneTryptophane Niacin, SerotoninNiacin, Serotonin
Arginine,Arginine,
Methionine, GlycineMethionine, Glycine
CreatineCreatine

28. Last edited Nov 2018
1. Describe biomedical significance of five biologically active
peptides.
2. List two examples of dipeptide and their biomedical
importance.
3. List amino acids present in glutathione . Write its
significance.
4. What is ADH? Write its function.
5. Define Zwiter ion and write its significance.
6. Explain amphoteric nature of amino acid.
7. List Branched chain and Aromatic amino acids.
8. Describe classification of amino acids.

29. What is happening? Can you understand?