Monday July 27 2015 Exam 4 Lecture 31 1 Protein Degradation Dietary Cellular Amino acid Catabolism Inborn Errors of Metabolism Amino Acids Catabolism Notes 2 CATABOLISM OF DIETARY PROTEINS Pepsinogen Zymogen Pepsin Active enzyme Synthesized and released into stomach and activated by low pH Non specific cleavage of protein Proteolysis of Dietary Protein Begins in Stomach Low pH also denatures proteins Random coils accessible to protease Synthesized and released into the stomach as pepsinogen in low pH pepsinogen unfolds and cleaves itself autocatalytic 1 Monday July 27 2015 Notes Pepsin hydrolyzes proteins in a non specific manner Pepsinogen cleaves dietary proteins With the low pH proteases get access to the proteins when the zymogen unfolds it can clip 44 residues out of the inactive zymogen to for the active enzyme pepsin Pepsinogen become denatured in a pH of 5 or higher 3 CATABOLISM OF DIETARY PROTEINS Pancreatic Proteases Released as zymogens Cleave proteins at specific residues Enteropeptidase Activates pancreatic protease cascade Oligo peptides proteolyzed aminopeptides in luminal surface Di and Tri Peptides cleaved by peptidases in enterocytes Amino acids are used in synthetic reactions or catabolized Notes catabolism continues in the duodenum first part of small intestine this is done by proteases in the pancreas and zymogens that are released into the duodenum Pancreatic proteases cleave proteins at certain residues as part of a protolytic cascade Begins with peptidase which is in enterocytes line lumen of small intestine Peptidase turns the zymogens into active enzymes the enzymes cleave protein to make short oligo peptides Then cleaved more by amino peptidases and made into Di and Tri peptides to get into the cell Free amino acids can enter the cell easily 4 GASTRIC AND PANCREATIC ZYMOGENS Pancreas Zymogen Chymotrypsinogen Active Enzyme Chymotrypsin Zymogen Trypsinogen Active Enzyme Trypsin Zymogen Procarboxypeptidase Active Enzyme Carboxypeptidase 2 Monday July 27 2015 Zymogen Proelastase Active Enzyme Elastase Stomach Zymogen Pepsinogen Active Enzyme Pepsin Notes proteolytic cascade activated by enteropeptidase enzyme that is found on the lumen forms the zymogens that later can be activated to active enzymes KNOW THE PATHWAY AND NAMES OF THE ENZYMES Stomach pepsinogen is activated by low pH Pancreas zymogens are activated by proteolysis AMINO PEPTIDASE attack at amino end of protein to release amino acids one after another Carboxypeptidase cleave proteins are carboy terminus 5 Pepsin is active only in a low pH environment at pH values 6 5 and greater it becomes inactive Why is this characteristic important for proteolysis in the duodenum Pancreatic proteolytic zymogens enter the duodenum along with bicarbonate and mix with the dietary contents just leaving the stomach What effect does bicarbonate have Notes Bicarbonate ion raises the pH 7 Important for proteolysis because pepsin cleaves proteins randomly and by increasing the pH and deactiving pepsin it is prevented from proteolyzing the zymogens and enzymes in small intestine 6 CATABOLISM OF CELLULAR PROTEIN Regulation through turnover Quality control mistranslated misfolded oxidized 3 Monday July 27 2015 Source of amino acids Anabolic metabolites Source of fuel Notes Regulated by turnover by getting rid of the protein you can get rid of the activity either activating or inhibiting effect on pathway Quality control protein is wrong shape can lead to huntington disease alzheimers Source of amino acids 7 CATABOLISM OF CELLULAR PROTEIN Cellular proteins are ubiquitinated and degraded by the proteasome END ON VIEW Looking down into the proteasome through 19S opening Notes 8 Ubiquitin binds to proteins through formation of an isopeptide bond with Lysine residues Notes The more ubiquitin molecules bonded together the stronger the signal is to get the protein to the protosome 9 CATABOLISM OF CELLULAR PROTEIN Cellular proteins are ubiquitinated and degraded by the proteasome The whole proteasome is 26S END ON VIEW Looking down into the proteasome through 19S opening Notes 19S regions on top and bottom and 20S in middle 20S is catalytic region that breaks down the proteins 10 19S 4 Monday July 27 2015 ATPase Isopeptidase 20s conformational change Notes the ubiquinated protein binds to the 19S cap and the ATPase and 19S cap remove the uniquitin the ATPase and 19S cap unfold the protein and let it enter the 20S region They are attacked by Threonines to make peptide fragments peptides are cleaved to 7 9 amino acids and leave through other 19s region 11 Peptide Fragments TCA Cycle Notes peptide fragments are further broken down into amino acids that can be left intact for biosynthesis or broken down and exposed by urea cycle Or carbon skeletons are used in glucose or glycogen synthesis or fatty acid synthesis or cellular respiration 12 AMINO ACID CATABOLISM Where Liver Major site of amino acid catabolism Muscle Branched chain amino acids Basic Strategy Remove amino group NH4 Utilize the carbon skeletons Synthesis or energy Notes 13 Which three are branched chain amino acids 5 Monday July 27 2015 Notes Leu Ile and Val 14 AMINO ACID CATABOLISM Where Liver Major site of amino acid catabolism Muscle Branched chain amino acids Basic Strategy Remove amino group NH4 Utilize the carbon skeletons Synthesis or energy Notes 15 AMINO ACID CATABOLISM Fate of Amino Groups First of all be careful Amonium is toxic 50 umol L Normal High levels can cause lethargy gait disturbances headache vomiting seizures cognitive deficit NH4 Used for synthesis of nitrogen containing compounds Excess converted to urea cycle Notes 16 BASIC CATABOLIC PROGRESSION Transdeamination Amino Transfer Transfer amino group to an alpha ketoacid usually to alpha kteoglutarate to yield glutamate Deamination Oxidative deamination to remove the amino group as ammonium ion 6 Monday July 27 2015 Notes 17 USE OF CARBON SKELETONS 7 Carbon Skeleton Metabolites Anabolic precursors Energy production Glucose for brain RBCs Acetyl CoA TCA Cycle intermediates Notes What we are left with Pyruvate Acetyl CoA Acetoacetyl CoA alpha Ketoglutarate Succinyl CoA Fumarate Oxaloacetate KNOW THESE they can be used for anabolic precursusors or energy production 18 TRANSAMINATION Notes Aspartate comes in and loses amino group and becomes OAA then alpha Ketogluatarate comes in and accepts the amino group and become Glutamate 19 AMINOTRANSFERASE REACTION Prosthetic group Pyridoxal Phosphate PLP