Protein Metabolism YR1 Lecture 1H 2022 PDF

Protein Metabolism Dr. Victoria Mansour School of Medicine [email protected] COPYRIGHT COMMONWEALTH OF AUSTRALIA Copyright Regulations 1969 WARNING This material has been reproduced and communicated to you by or on behalf of University of Western Sydney pursuant to Part VB of the Copyri...

Protein Metabolism Dr. Victoria Mansour School of Medicine [email protected] COPYRIGHT COMMONWEALTH OF AUSTRALIA Copyright Regulations 1969 WARNING This material has been reproduced and communicated to you by or on behalf of University of Western Sydney pursuant to Part VB of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. Do not remove this notice. Learning Objectives Describe how amino acids can come from the digestion of dietary protein breakdown, ubiquitin-mediated proteolysis and endogenous synthesis Describe how the general structure of amino acids can be used in metabolism, with a focus on carbon skeleton reuse, the urea cycle and glucose-alanine cycle Proteins  Long polymers of amino acids  General structure  20 amino acids http://www.mun.ca/biology/scarr/iGen3_06-01_Figure-Lsmc.jpg  9 essential  diet  Not a primary energy reserve  Structural and Functional roles  So how do we use amino acids?  Used for de novo protein synthesis  Amino acid synthesis  Energy & storage  Excretion https://figures.boundless-cdn.com/18576/large/figure-03-04-09.jpeg Boron and Boulpaep. Medical Physiology (2nd Edition) (2012) Proteins to amino acids - exogenous  Dietary protein  Present in meat, poultry, fish, tofu, chia, quinoa  Digested in the small intestine  initiated by pepsin in stomach  luminal, brush border, and cytosolic peptidases  Can be absorbed as oligopeptides and single amino acids  Amino acids exit the basolateral membrane into bloodstream Boron and Boulpaep. Medical Physiology (2nd Edition) (2012) Proteins to amino acids - endogenous  Proteins are constantly being degraded and synthesized depending on body demands/cell requirements  Protein turnover  Polyubiquitination marks proteins for degradation  Ubiquitin: a small protein of 76 amino acid residues  Monoubiquitation stimulates transcriptional activation  Large cytoplasmic complex of proteolytic enzymes—the proteosome—degrades the ubiquitinated proteins Stewart H. Lecker et al. JASN 2006;17:1807-1819 Proteins to amino acids – endogenous Amino acid biosynthesis  General reaction for the synthesis of amino acid Amino acid – NH3 α-Keto acid α-Keto acid Amino acid – NH3  Usually glutamate is the primary donating amino acid  Transamination  Carried out by aminotransferases  vitamin B6  Their production can be classed by their precursor  3-Phosphoglycerate  Pyruvate  α-Ketoglutarate (α-KG)  Oxaloacetate (OAA) GLYCOLYTIC INTERMEDIATES KREBS CYCLE INTERMEDIATES Proteins to amino acids – endogenous Amino acid biosynthesis Glucose Arginine Glycine Cysteine Serine 3-PG Citrulline Pyruvate Alanine Ornithine Acetyl-CoA Asparagine Aspartate OAA α-KG Glutamate Glutamine Proline Abbreviations 3-PG – 3-phosphoglycerate OAA – oxaloacetate α-KG – alpha ketoglutarate DIET Phenylalanine Tyrosine Protein and amino acids When demand is met?  When amino acids are in excess Amino acid  Reuse of carbon skeletons  Gluconeogenesis Glucogenic  Fatty acid synthesis Ketogenic α-KG α-keto acid Carbon skeletons Glutamate Some are both – Ile, Phe, Tyr, Thr, Trp NH4+  Excretion of nitrogen  Why do we need to excrete excess nitrogen?  How do we excrete the excess nitrogen?  All occurs in the liver Urea Cycle Garret and Grisham, Biochemistry 4th edition (2010) Protein and amino acids Synthesis vs. Degradation Keto-acid Amino Acid Synthesis Amino acid Degradation Keto-Acid Pyruvate Alanine Glutamate Orthinine* Proline Glutamine Citrulline* Arginine Serine Glycine Tryptophan Pyruvate αlpha-ketoglutarate Alanine Cysteine Threonine Aspartate Asparagine Lysine Phenylalanine Acetyl-CoA Oxaloacetate Leucine Tyrosine 3-phosphoglycerate Serine Cysteine Glycine Isoleucine Threonine Leucine Tryptophan Acetoacetate Arginine Glutamate Histidine Glutamine Proline αlpha-ketoglutarate Synthesis is not equal to degradation Isoleucine Valine Methionine Succinyl-CoA Asparagine Phenylalanine Tyrosine Fumarate Asparagine Arginine Oxaloacetate Protein and amino acids When demand is met? AA – NH3 METABOLISM α-Keto acid EXCRETION Glutamate via urine AA – NH3 Mitochondrial matrix α-KG α-KG Glutamate SECRETION Deamination Glutamate dehydrogenase into Blood H2O 1 Carbamoyl-phosphate synthetase I (CPS-I) 2 Ornithine transcarbamoylase (OTC) 3 Argininosuccinate synthetase (ASS) 4 Argininosuccinate lyase (AL) 5 Arginase Arginine Fumarate 4 Argininosuccinate Cytosol NH3 + CO2 UREA 5 Ornithine UREA CYCLE 3 Aspartate Ornithine 2 Citrulline Citrulline 1 2ATP 2ADP + Pi Carbamoyl-P Proteins What role do they play when intake is low?  Small contributions can come from protein degradation to energy requirements  normal resting state  10% protein, 90% carbs & fats Any reason why we would limit the use of protein as a source for energy?  However, during specific circumstances proteins contribute somewhat to providing energy  Short-term starvation but not prolonged starvation  Primarily from muscle  The breakdown of muscle protein for energy  Transamination  alanine http://rlv.zcache.com/hungry_cartoon_pig_cartoon_starving_pig_tshirtp235689355928148085yxkr_400.jpg Proteins What role do they play when intake is low? Blood Muscle Liver UREA α-KG Alanine Alanine Transamination UREA Glutamate Deamination Glutamate dehydrogenase α-KG α-Keto acid Glutamate AA – NH3 Transamination Alanine transaminase (ALT) UREA CYCLE Alanine METABOLISM Alanine transaminase (ALT) Pyruvate Pyruvate Proteolysis Glucose Glucose Glucose Proteins Diet PROTEINS TAG breakdown Galactose Glucose Protein breakdown Glycogen G-6-P Adipose tissue Glycogenolysis/glycogenesis FA Glycerol DHAP Fructose G-3-P Fatty acid oxidation Fatty acid synthesis Glycolysis/gluconeogenesis CARBOHYDRATES FATS Protein synthesis AA 3-PG Lactate Pyruvate Acetyl-CoA Ketone bodies ATP Muscle Electron transport chain Abbreviations Krebs Cycle Urea G6P – glucose 6 phosphate DHAP – dihydroxyacetone phosphate G3P – glyceraldehyde 3 phosphate 3-PG – 3-phosphoglycerate FA- fatty acids AA – amino acids TAGs - triacylglycerides Clinical relevance: Nutrition and Health Urea cycle disorders (UCDs) Phenylketonuria (PKU) 1 Carbamoyl-phosphate synthetase I (CPS-I)^  Genetic mutation in the PKU gene (phenylalanine hydroxylase)^ 2 Ornithine transcarbamoylase (OTC) #  Phenylalanine cannot be converted to Tyrosine 3 Argininosuccinate synthetase (ASS) ^ 4 Argininosuccinate lyase (AL) ^ 5 Arginase ^ EXCRETION  Build up of phenylalanine  toxic into Blood  Is usually diagnosed early after birth  Neonatal screening test Mitochondrial matrix  Affects 1 in 10, 000 babies  Other diseases related to errors in phenylalanine/tyrosine catabolism  Alkaptonuria  Tyrosinemia (3 types)  Albinism Malnutrition/Malabsorption H2O KREBS Arginine Fumarate 4 Argininosuccinate 5 Ornithine UREA CYCLE 3 Key ^ - autosomal recessive # - X- linked Cytosol NH3 + CO2 UREA Aspartate Citrulline Ornithine 2 Citrulline 1 2ATP 2ADP + Pi Carbamoyl-P Summary  Amino acids can come from  Exogenous sources  diet  Endogenous sources – protein degradation and/or transamination (ketoacids/amino acids)  Amino acids can be used for amino acid/protein synthesis, as an energy source or stored  Excess amino acids – carbon skeletons are recovered  Gluconeogenesis  Lipogenesis  Amine group excreted  UREA CYCLE https://au.pinterest.com/pin/192317846561562980/  During short term starvation muscle can be used as a source to provide energy  GLUCOSE-ALANINE CYCLE Quiz Questions  Dietary protein can be broken down and absorbed in the small GIT. Which statement about this process is FALSE? A) B) C) D) E) Digestion begins in the mouth Gastric and pancreatic peptidases digest in the intestinal lumen Cytosolic peptidases degrade absorbed oligopeptides Amino acids and oligo peptides can be absorbed by enterocytes Amino acids leave basolaterally via transporters  What is the reaction that takes place for the synthesis of amino acids? A) B) C) D) Deamination Amination Transamination Cisamination Questions Links and Resources  Garret and Grisham, Biochemistry 4th edition (2010)  Boron and Boulpaep, Medical Physiology 2nd edition (2012)  Guyton and Hall, Textbook of Medical Physiology 13th edition (2016)  Berg JM, Tymoczko JL, Stryer L. Biochemistry. 5th edition. New York: W H Freeman; 2002. Section 30.2, Each Organ Has a Unique Metabolic Profile. Available from: https://www.ncbi.nlm.nih.gov/books/NBK22436/  Disorders of carnitine transport and the carnitine cycle. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2557099/ Extra reading for interest  http://www.newbornscreening.info/Parents/fattyaciddisorders/CTD.pdf Thank you  Lecture feedback Contact Details Dr. Victoria Mansour Associate Lecturer in Medical Education Medical Education Unit Year 1 PBL Coordinator PBL tutor Curriculum Roadmap Coordinator Western Sydney University [email protected] Phone 02 46203751 Office 30.3.14 Available Mon, Tues, Thurs & Fri