Glycine is an aliphatic amino acid which gives rise to many vital derivatives. This is a non-essential amino acid. This presentation is targeted for MBBS, MD, BDS and general Biochemistry students.

1. METABOLISM OF GLYCINE
Prof (Dr)Viyatprajna Acharya
MD, PhD (Biochemistry)

2. OverviewofAAMetabolism
 12 out of 20 AA- synthesised from intermediates of
Glycolysis &TCA cycle
 8 AA- essential AA; what are they?
(I Love & Like To Take Potato Very Much)
 Out of 12 NEAA- 9 from amphibolic intermediates
 Rest 3 NEAA- Cys,Tyr, Hyl - from essential AA

3. CatabolismofAA
 Amino group- Urea
 C-skeleton- 7 products
Pyruvate
Acetyl Co-A
Acetoacetyl-CoA
α-Ketoglutarate
Succinyl Co-A
Fumarate
Oxaloacetate

4. Summary of catabolism of AA

5. Ketogenic AA– AA that are degraded to Acetyl CoA or
acetoacetylCo-A→ Ketone bodies
Lysine & Leucine- Purely ketogenic

6. GlucogenicAA
AA that are degraded to Pyruvate, α- ketoglutarate,
Succinyl CoA, Fumarate or Oxaloacetate
Both Ketogenic & Glucogenic AA- Phe, Tyr, Trp & Ile

8. INDIVIDUAL AA

9. GLYCINE
 Simplest AA
 Non-essential
 Glucogenic

10. Synthesis
1. From serine- removal of hydroxymethyl group
from Ser
2. From Threonine- byThr aldolase activity
3. By Glycine synthase system- From CO2 , NH3
& 1-C unit; reversal of Gly cleavage system

12. 4. Aminotransferase reaction- from Glyoxylate,
Glutamate or alanine
5. From Choline
Choline
dehydrogenase Betaine
dehydrogenase
Methyltransferase
Sarcosine
demethylase
Sarcosine
oxidase

13. Catabolism
1. Oxidative deamination by Glycine cleavage
system- Multi-enzyme complex

14. 1. Glycine dehydrogenase (decarboxylating)
2. Aminomethyltransferase
GLYCINE CLEAVAGE SYSTEM OF LIVER MITOCHONDRIA

15. 2. Glucogenic pathway- first gets converted to Ser-
Reversal of serine hydroxymethyl transferase
reaction
Ser → Pyruvate

16. 3.Biosynthesisoffollowing-
Creatine, Creatine phosphate &
Creatinine
Heme
Purine nucleotides
Glutathione
Conjugating agent
Neurotransmitter

17. Creatine & creatine phosphate
(MAG)

18.  During muscle contraction, energy is first
derived from hydrolysis of ATP
 Creatine kinase is present in – muscle, brain &
liver
 ATP regenerated by hydrolysis of creatine
phosphate- LOHMANN’S REACTION
 CK- where utilised?

19.  Serum Creatinine level- 0.2-1.2 mg/dl
 Creatine:
• Dietary supplement
• Used to improve athletic performance
 Creatinine:
• Urinary excretion generally constant;
 proportional to muscle mass
 Creatinine Clearance Test:
• Compares the level of Creatinine in urine (24 hrs.)
with the Creatinine level in the blood
• Used to assess kidney function
• Important determinant in dosing of several drugs
in patients with impaired renal function

20. Heme synthesis

21. Purine nucleotides

22. 4. As a constituent of protein
Plays a vital role in protein structure- present in
turns & bends
Every 3rd AA in collagen is Glycine

23. GLUTATHIONE (GSH)
 Tripeptide
 Gamma-glutamyl-cysteinyl-glycine
 Widely distributed in all tissues
 GSH: GSSH (Reduced : oxidised) ratio is
maintained at 100:1 by glutathione reductase

25. Functionsofglutathione
 Component of antioxidant enzyme
glutathione peroxidase- scavenge free
radicals
 Maintains RBC membrane integrity. Protects
Hb from getting oxidised by H2O2
 Transport of AA- Meister cycle
 Detoxification of drugs by increasing their
solubility
 Disulfide linkages in protein structure
 Acts as a cofactor for some enzymes.

26. Conjugating agent
 Conjugating bile acids
 Detoxification of benzoic acid → Hippuric
acid

27. As neurotransmitter
 Modulates NMDA
neurotransmission
 Moderate qty- inhibitor
 High levels- over-excitation

28. Metabolic errors
1. Primary hyperoxaluria -
Glyoxylate pathway affected-hereditary
defect in the enzyme Glycine transaminase-
Glyoxylate accumulates- ↑ urinary oxalate
irrespective of dietary intake
Protein targeting defect – enz seen in
mitochondria instead of peroxisome
Nephrolithiasis, renal colic, hematuria
2. Nonketotic Hyperglycinemia –
Defect in Glycine cleavage system
Severe mental retardation & seizures

30. WWW.VPACHARYA.COM
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