Dr. Satyendra K Sinha Asst. Prof. Zoology Ram Jaipal College, Jpu, Chapra Zoology M.Sc. Semester 2 Paper V AMINO ACID DETOXIFICATION Amino acid detoxification or protein Detoxification is the process by which proteins containing methylated arginine are broken down and removed from the body. Arginine (Arg) is a non-essential amino acid and one of the most commonly occurring natural amino acids. The Australian physician Trevor Tingate coined the term protein detoxification in 2010. Arginine (Arg) A Non/Semi-essential amino acid Methylated arginine is a modified version of arginine (Post Translational Modification). Methylation of protein arginine plays an important role in the regulation of many cell processes including gene transcription, cell signal transduction, DNA repair and RNA processing. Protein turnover releases the free methylated arginine derivatives- 1. Asymmetric Dimethyl arginine (ADMA) 2. Methyl arginine (L-NMMA) 3. Symmetrical dimethyl arginine (SDMA) Asymmetrically methylated forms of arginine are toxic released during protein turnover. The protein detoxification pathway Eliminates free methylated-arginine derivatives from the cell. Symmetrically methylated forms are not toxic and are excreted unchanged by the kidney. Asymmetrically methylated forms however are toxic and broken down by the enzyme dimethyl arginine dimethylaminohydrolase (DDAH). Impairment of DDAH function slows breakdown and increases the level of toxic asymmetrically methylated arginine forms. Long term exposure to these toxic amino acids is associated with endothelial dysfunction, arterial stiffness, insulin resistance, chronic kidney disease, heart disease, dementia and ageing Protein detoxification pathway aim to: • Reduce intracellular levels of free asymmetrically methylated arginine derivatives, • Slow the ageing process • Delay the development of disorders associated with ageing. PRMTs (Protein Arginine Methyl transferase) Protein arginine methyltransferase's (PRMTs) are activated by shear stress &LDL cholesterol. Two types of PMRTs have been characterized. Type 1 PRMTs Are found mainly in endothelial and smooth muscle cells and produce methylated proteins containing ADMA and L-NMMA. Type 2 PRMTs Produce proteins that contain SDMA and L-NMMA DDAH (Dimethyl Arginine Dimethylaminohydrolase) DDAH activity is inhibited by NO Reactive oxygen species (ROS) and L-arginine. Two isoforms of DDAH have been identified. 1.DDAH-1 is found in tissues expressing neuronal NOS (nNOS) and in the liver, kidney and lung. Expression is increased by IL-1β and Inhibited by oxLDL and TNF. Plasma levels of ADMA reflect DDAH-1 activity. DDAH-2 is found in tissues expressing endothelial NOS (eNOS) and inducible NOS (iNOS). Expression is increased by NADPHox, all trans retinoic acid, pioglitazone and estradiol Inhibited by hypoxia, hyper glycaemia and LPS. Schematic outlining the synthesis and metabolism of ADMA and SDMA. Protein arginine methylation is performed by a family of enzymes termed protein arginine methyltransferases (PRMTs), which methylate protein-incorporated L-arginine residues to generate protein- incorporated NG monomethyl-L-arginine. Type I PRMTs generate asymmetric dimethyl arginine ADMA and Type II PRMTs convert NMMA to symmetric dimethyl arginine SDMA. Protein-incorporated L-arginine residues can also be converted to citrulline by peptidylarginine deaminases (PADs), thereby blocking methylation on the arginine residue. Upon proteolytic cleavage of arginine-methylated proteins, free ADMA and SDMA are released into the cytoplasm. ADMA and SDMA can be moved out of the cells via cationic amino acid transporter (CAT) and transported to other organs or excreted in urine. ADMA can be converted to L-citrulline and dimethylamine by dimethylarginine dimethylaminohydrolase-1 (DDAH-1) and -2 (DDAH-2). Alanine-glyoxylate aminotransferase 2 (AGXT2), a mitochondrial aminotransferase expressed primarily in the kidney, can metabolize ADMA as well as SDMA. ADMA can be transaminated by the enzyme AGXT2 to α-keto-δ-(NG,NG-dimethylguanidino) valeric acid (DMGV) Role of Amino Acid detoxification in Diseases- Asymmetrically methylated arginine forms (AMAF) inhibit nitric oxide synthase and the formation of nitric oxide (NO), also known as 'endothelium-derived relaxing factor', or 'EDRF'. Nitric oxide is critical to blood vessel function and inhibition leads to an increase in arterial stiffness due to vasoconstriction. Indeed, by protecting the vessel against vasoconstriction nitric oxide has been referred to as the fountain of youth. It also protects blood vessels by inhibiting platelet activation, smooth muscle proliferation and endothelial cell activation. Reduced arterial stiffness protects the heart. Asymmetrically methylated arginine forms by contrast inhibit NOS, reduce nitric oxide and increase central arterial pressure. Long-standing arterial stiffness inevitably leads to heart failure, kidney failure and dementia; the three leading causes of death in later years. Protein detoxification removes free methylarginines that would otherwise inhibit the generation of nitric oxide. ---------------------------------------------------------------------------------------------------- .