It is the simplest amino acid. It is non-essential and is glucogenic.

1. GLYCINE
M.Prasad Naidu
MSc Medical Biochemistry,
Ph.D.Research Scholar

2. GLYCINE :
• It is simplest aminoacid
• Nonessential and glucogenic.
Formation of glycine:
1. From serine
2. From threonine
3. By glycine synthase reaction

3. By Glycine synthase:
NADH + + H+ NAD+
CO2 + NH4+ glycine
N5 , N10 –methylene THF THF
Glycine synthase is a multienzyme complex and
requires PLP , NAD and THF.

4. Metabolic functions of glycine:
Glycine is used for biosynthesis of
1. Heme
2. Purine ring
3. Creatine
4. Glutathione
5. As a conjugating agent
6. Glycine as neurotransmitter
7.Glycine as a constituent of protein

5. 1.Heme synthesis
ALA synthase
glycine + succinyl CoA δ-aminolevulinate
PLP
This is the rate limiting step in heme synthesis.

6. 2. Purine ring – the whole molecule of glycine is
incorporated into purine ring (C4 ,C5 and N7).
synthetase
5-phosphoribosyl-1-amine glycinamide ribonucleotide
+GLYCINE
ATP ADP + Pi

7. 3. Synthesis of creatine
Arginine + Glycine
Kidney Arginine- glycine
transamidinase
Guanidoacetate
Guanidoacetate methyltransferase Liver
Creatine
Creatine kinase
Creatine Phosphate
SAM
SAH
ATP
ADP
CREATININE
H2O
Pi
MUSCLE

8. Creatine is reversibly phosphorylated to creatine
phosphate by creatine kinase and stored in muscle as
high enegy phosphate.
Creatinine :
it is anhydride of creatine
it is formed by cyclisation of creatine.

9. Serum creatinine – 0.7 -1.4 mg/dl
Urine creatinine – 1- 2 g/day
Serum creatinine concentration is not influenced by
endogenous or exogenous factors, so used as a more
reliable indicator of renal function.

10. 4.Synthesis of glutathione

11. Superoxide dismutase Peroxidase
O2
- (superoxide) H2O2 H2O
i)Freeradical scavenging 2GSH GS– SG
Glutathione reductase
2NADP+ NADPH+H+
Glucose -6-phosphate GPD
By scavenging free radicals it maintains RBC
membrane integrity.

12. iii)Involved in amino acid transport – Meister cycle
iv)Insulin inactivation by
hepatic insulin glutathione transhydrogenase
Insulin(A+B chains)+ 2GSH GS—SG+A chain +B
chain
v) Activation of enzymes : Many enzymes having –SH in
active site are kept in the active form by glutathione.
Ex: glyceraldehyde -3-P dehydrogenase

13. vi)Met-hemoglobin: glutathione is necessary for the
reduction of met-Hb(ferric) normal Hb (ferrous state).
The met-Hb is can not transport oxygen .
2Met-Hb-(Fe3+ ) +2 GSH 2 Hb-(Fe2+) + 2H+ + GSSG

14. 5. Conjugating agent
It is used for conjugating bile acids so that their
amphipathic property is increased.
Cholic acid + Glycine glycocholic acid
Chenodeoxycholic acid glycochenodeoxycholic
+ Glycine acid
Glycine + Benzoic acid benzoyl glycine
( hippuric acid)

15. 6.Glycine as neurotransmitter:
 It is a neurotransmitter in the brainstem and spinal
cord.
 At moderate levels it disrupts neuronal traffic; but at
very high levels it causes overexcitation

16. 7.Glycine as a constituent of protein
 It is seen where the polypeptide chain bends or turns.
 In collagen , every third aminoacid is glycine.