S TAGES OF A MINO A CIDS C ATABOLISM Dr. Samah Kotb Lecturer of Biochemistry 2015 Cellular Biochemistry and metabolism 2 CLS 333

S TAGES OF A MINO A CIDS C ATABOLISM C HAPTER 8

Amino acids are the building blocks of the proteins. Twenty amino acids are commonly found in proteins. INTRODUCTION

4 Amino acids are essentially α-amino acids:

 They differ from each other in their side chains, or R groups, which vary in structure, size, and electric charge, and which influence the solubility of the amino acids in water. INTRODUCTION

Arginine (Arg) Threonine (Thr) Lysine (Lys) Valine (Val) Phenylalanine (Phe) Tryptophan (Trp) Methionine (Met) Histidine (His) Leucine (Leu) Isoleucine (Ile) 6 Essential Amino Acids

Only 10 % of the daily energy requirements of an average adult are provided by amino acid degradation. This is not high when compared to monosaccharide (50%) and fatty acids (40%). Catabolism of Amino Acids in Animal Tissue

Amino acids entering cells are primarily used by the cells for synthesize of various structurally or biologically important proteins such as enzymes and hormones. Catabolism of Amino Acids in Animal Tissue

The remaining amounts of amino acids after sufficient proteins have been synthesized are now degraded to produce energy equal to 10 % of the daily requirements. Catabolism of Amino Acids in Animal Tissue

20 amino acids catabolism give 10 % of daily energy requirements. Catabolism of Amino Acids in Animal Tissue

There are 2 stages of amino acid catabolism:-  STAGE 1: Removal of the primary amino groups by an enzymatically catalyzed reaction known as TRANSAMINATION catalyzed by enzymes known as TRANSAMINASES. Stages of Amino Acids Catabolism

 STAGE 2: Degradation of the remaining keto-acids into acetyl- Co A or other TCA cycle intermediates. Stages of Amino Acids Catabolism

The α amino group of the amino acid is enzymatically transferred to an acceptor molecule namely α- ketoglutarate leaving behind the corresponding keto acid. α-ketoglutarate becomes aminated and yields glutamate:- Stage 1: TRANSAMINATION (Deamination)

α-ketoglutarate serves as the universal acceptor of amino groups during the transamination of all 20 amino acids. However a specific transaminase is required for each of the 20 amino acids. Eg:- Stage 1: TRANSAMINATION (Deamination)

Glutamate undergoes oxidative deamination to remove the amino groups which appears as ammonia. The reaction is catalyzed by the enzyme Glutamate Dehydrogenase which uses NAD + as a coenzyme. (a mitochondrial enzyme). Ammonia is formed from Glutamate (Fate of Glutamate):

 As a result of transamination 20 different ketoacids are formed.  Each of the 20 ketoacids is oxidized by a specific pathway and end up as either acetyl-CoA or one of the TCA cycle intermediates.  Some of these oxidative pathways are simple, whereas others are complex & multistep. Stage 2: Oxidation of Ketoacids

1. Examples of oxidation of Ketoacids:

2. Stage 2: Oxidation of Ketoacids:

3. Stage 2: Oxidation of Ketoacids:

4. Stage 2: Oxidation of Ketoacids:

Oxidation of ketoacids of corresponding amino acids