Glycine

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 : From serine From threonine By glycine synthase reaction

3. By Glycine synthase : NADH + + H + NAD + CO2 + NH4 + glycine N 5 , N 10 –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 Heme Purine ring 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 H 2 O 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 O 2 - (superoxide) H 2 O 2 H 2 O 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-(Fe 3+ ) +2 GSH 2 Hb-(Fe 2+ ) + 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.