BMS100 Amino Acid Metabolism PDF

Amino acids Overview Dr. Heisel BMS100 Objectives Define the properties of amino acids at pH=7 Provide an overview of the N-cycle Define what is meant by essential amino acid and list the EAA’s and BCAA’s Categorize the amino acids by polarity, describe the properties of each category and any u...

Amino acids Overview Dr. Heisel BMS100 Objectives Define the properties of amino acids at pH=7 Provide an overview of the N-cycle Define what is meant by essential amino acid and list the EAA’s and BCAA’s Categorize the amino acids by polarity, describe the properties of each category and any unique groups  - + At pH = 7 aa’s are: - “zwitterions”: no net charge across N- & C- terminals - “amphoteric”: can accept (which end?) or donate (which end?) H+ * Amino Acids: Classifications Essential amino acids (EAA) Not made de novo in mammals: required in diet Valine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan Infants: histidine and arginine are also considered essential in infants, but not in adults Infants do not yet make sufficient amounts 4 * Amino Acids: Classifications Any and Arg both EAA’s: Required in diet have only 1 “A” (alanine and aspartate have 2 or 3)  Any = Arginine – infants First 2 amino acids  Help = Histidine (H) – infants in list = “youngest”  In = Isoleucine (I) = infants  Learning = Leucine  These – Threonine (T) Both aa’s that start  Little = Lysine with “L” are  Molecules = Methionine (M) essential  Feels = phenylalanine (sounds like fenylalanine) (F)  Truly = Tryptophan  Valuable = Valine (V) 5  Classifications: Polarity and Charge Neutral - Non-polar - Aliphatic - Aromatic - Polar Charged - (-)ve - (+) ve Grey area = cys & tyr SH has borderline polarity Tyr has a polar OH group, but benzene ring is large and non- For Reference Amino Acid Only: Amino Acid Alanine Ala A Codes Asparagine Asn N Aspartate Asp D Arginine Arg R Won’t be Cysteine Cys C tested, but Glutamate Glutamine Glu Gln E Q 3-letter Glycine Gly G codes will Histidine His H Isoleucine Ile I be used in Leucine Leu L lectures Lysine Lys K Methionine Met M Phenylalanine Phe F Proline Pro P Serine Ser S Threonine Thr T Tryptophan Trp W Tyrosine Tyr Y Valine Val V Neutral Non-Polar Aromatic (benzene ring) or aliphatic (non-benzene hydrocarbon chain) Tyr sometimes Cys sometimes grouped with neutral grouped with neutral polar aa’s polar aa’s Neutral Non-Polar Unique groups - Proline Preview: Cannot rotate freely around α-C, so not found in protein structures that require rotation (ex α-helix) α- No C α- rotatio C n Rotation R Neutral Non-Polar Unique groups – Cysteine Thiol group can form disulfide bonds 2 H+ Part of many important proteins and peptides: Keratin (hair and nails) Insulin (lowers blood sugar) Glutathione (GSH): Gly-Cys- Glu Antioxidant Insulin From H2O + Cys H2O GSH + GSH 2 H2O GS-SG Held together by disulfide bond until regenerated NADP+ NADPH + H+ NADPH = coenzyme form of ? Neutral Non-Polar Unique groups - Methionine Has a S Met and Cys are the only 2 aa’s with a S Can it form disulfide bonds? Neutral Non-Polar In General: Food ingested/digested  nutrients absorbed BCAA’s: Val, Leu, Iso from small intestine  blood  liver  Branched chain amino acids blood  other Subset of the essential amino acids tissues Highly enriched in blood leaving liver Liver changes profile of ingested aa’s  increased proportion of BCAA’s BCAA’s carry N to other tissues for use Neutral Polar Hydroxy (OH) R- groups: Site for phosphorylation Preview: Important in regulation of enzyme Hydroxy andactivity amido R-groups: and signal Review: What type of non-covalent bonding transduction can both participate in? Charged: Acidic and Basic His often picks up an H+ to become charged At pH = 7: Acidic = negatively charged Charged molecules pKa range for a weak acid? participate Basic = positively chargedin what type pKa range for a weak base? of bonding? Amino acid Metabolism Anabolism and Catabolism Dr. Heisel BMS100 Objectives: Anabolism Describe the 2 ways N can be incorporated into amino acids List select amino acids in each anabolic family and outline their relationship to each other, including any important reactions Define PKU and its dietary considerations Outline the roles of histamine Amino Acid Anabolism Every amino acid includes at least 1 nitrogen There are 2 places this N can come from: NH4+ Directly incorporated, not transferred from another molecule An amino or an amido group Transferred over from a different molecule Direct Incorporation of an N Example: Creation of glutamine by directly adding an N (from NH4+) to glutamate NH4+ N replaces the O Glutamate Glutamine Transfer of an N Transfer of an amino or amido = transamination or transamidation, respectively For these reactions, you must recognize the relationship between select amino acids and alpha keto acids Amino acid R Keto acid O = R * Know these Amino amino/keto acids pairs!! Alanine Aspartate Glutamate Alpha ketoacids O= O = O = Pyruvate Oxaloacetate α- Transfer of an N to make amino acids Example: Creation of Ala and Asp by transamination Vitamin B6 coenzyme (PLP) helps transfer the amino group from amino acid “1” to keto acid “1” Amino Keto Keto Amino acid Results in acid creation of amino acid acid “2” and keto acid “1” acid “1” “2” ALT “2” “2” Glutamate + pyruvate alpha ketoglutarate + alanine AS T Glutamate + oxaloacetate alpha ketoglutarate + aspartate These 2 rxns typically happen in the liver ALT and AST = enzymes (Ala & Asp transaminases) Elevated levels of these enzymes in the blood Amino Acid Anabolism The 20 amino acids belong to one of 6 amino acid families that share a common precursor: Glutamate family Aspartate family Serine family Pyruvate family Aromatic family Histidine (no other aa’s in this family) Select Reactions: Glutamate family Glutamate Family Precursor = the keto acid partner of glutamate = ? Glu can then incorporate another N to become which amino acid? Select Reactions: Glutamate Family Alpha * Glutamate Glutamine ketoglutarate precursor O= * Important reaction in brain, see next slide FYI: Other family members = Pro and Arg Amino Acids: Glutamate Family * Enzyme for Glu to Gln = glutamine synthetase Highly concentrated in brain Neurotox ic Glutamin e Glu + NH4+ syntheta Gln se To liver for N-disposal via urea cycle Select Reactions: Aspartate family Aspartate Family Same pattern as Glu family Precursor = the keto acid partner of aspartate = ? Asp can incorporate another N to become what amino acid?   Same, except glutamate is glutinous/gre edy, has an extra CH2 Glutama Aspartat te e  Select Reactions: Aspartate Family Oxaloacetate Aspartate Asparagine precursor O =   Same, except glutamine is FYI: Other family glutinous/gre edy, has an members = Lys, Thr, extra CH2 Met Glutamine Asparagine  Amino Acids: Serine Family Vitamin Connection: B6 Vitamin Connection: - Coenzyme form = PLP B9 - Biochemical - Coenzyme form = function: transfer of folate sulfur - Biochemical (transulfhydration) Serine function: transfer of 1-C groups PLP transfers Folate picks up the a S from 1-C group from Ser another and transfers it molecule to something else, Ser to make turning Ser into Gly Cys Cysteine Glycine Select Reactions: Pyruvate and family Pyruvate is the precursor to: Pyruvate Its amino acid partner ? ? Isoleucin All BCAA’s (Iso, Val, Valine e Leu) Review: Leucine What is their main function? Which ones are essential? Select Reactions: Aromatic Family All aromatic aa’s are in this family Trp, Tyr, Phe Trp and Phe are EAA’s, but we can make Tyr from Phe Enzyme = phenylalanine hydroxylase Deficiency = PKU Aromatic Family: Application Clinical consideration: PKU (Phenylketonuria) Autosomal recessive disorder Deficiency in phenylalanine hydroxylase Build-up of Phe occurs Phe is converted to phenylketone, excreted in urine FYI: Symptoms include - Neurological problems such as progressive mental retardation and seizures Treatment Dietary: if caught early and stay on approved diet can have normal development What dietary recommendations would you make, and why? Objectives: Catabolism Describe the two main pathways for N to get from extra-hepatic tissues to the liver Outline the urea cycle, including: Location The names of the molecules involved Arginase enzyme Where the N’s for urea come from Amino Acids: Catabolism Not the opposite pathways to anabolism Requires deamination to produce a carbon skeleton and an ammonium ion Amino Acid Deaminatio n NH4+ Carbon Skeleton Urea Converted to Feeds into ketogenic (to urea in liver make ketone bodies) and/or and excreted in gluconeogenic (to make urine by glucose) cycles kidneys Amino Acids: Deamination 2 main deamination pathways: 1) General - Extrahepatic tissues* to liver: Glutamine synthetase reaction Results in glutamine carrying N to the liver to make urea Neurotox ic Glutamin e Glu + NH4+ syntheta Gln se To liver for N-disposal * In which tissue did we say this via urea rxn is particularly important, and cycle why? Amino Acids: Deamination 2 main deamination pathways: 2) Specific - Muscle to liver: Glucose-alanine cycle Results in alanine carrying N to the liver to make urea Other purpose of cycle: Results in liver making glucose for muscles Amino Acids: Deamination Glucose-alanine cycle What happens in working muscles: Glucose used for energy (glycolysis), makes pyruvate Pyruvate and glutamate undergo a transamination to make alanine and alpha ketoglutarate What happens in liver Reverse of previous transamination: Alanine and alpha ketoglutarate produce pyruvate and glutamate Pyruvate is used for GNG Glucose sent back to muscles for energy Glutamate releases nitrogen, nitrogen is excreted via urea cycle Glucose-alanine α KG Glu Working muscles breakdown Review: protein, use What glucose for vitamin energy helps with the trans- aminations ? N Why not incorporated into urea, just send travels to pyruvate to kidney, liver for excreted in GNG? urine NH + 4 C-skeleton α KG Glu Amino Acids: Urea cycle Urea cycle Occurs in liver Starts with carbamoyl phosphate Combines with ornithine to make citrulline A series of reactions then: Produces urea Regenerates ornithine: Urea Can be used to start cycle over again Amino Acids: Urea cycle Urea has 2 N’s; One from carbamoyl phosphate From where does the carbamoyl phosphate get the N? Glucose-alanine cycle or glutamine synthetase rxn result in N being transported to liver Deamination releases N  carbamoyl phosphate One from aspartate Glucose- alanine cycle Glutamin Aspartate N e transport synthetas ed to liver e reaction Urea  N from gln Urea synthetase rxn or Cycle glucose-ala cycle Arginase: only found in liver What is Cytosol the purpose of making urea: what happens to it next? From water Urea cycle * connects * to CAC via N from Aspartat fumarate carbamoyl N from e Phosphate Aspartate Amino Acids: Carbon skeletons Once the amino groups have been removed, the remaining C-skeletons can be classified as: Glucogenic (aka gluconeogenic) Used to make glucose Ketogenic Used to make ketone bodies Glucogenic and ketogenic – can fit into both groups Know * *Ala, Cys, pathwa Gly, Ser, ys Leu, Phe, Thr, Trp Ketogen Tyr Gluconeogen Pyruvate esis Acetoaceta esis te Acetoacyl Acetyl CoA CoA Trp, Lys *As Oxaloaceta te Thr, For any aa’s p only in blue Ile boxes, why *As Fumarate CAC Citrate are they not n also α-ketoglutarate glucogenic? Succinyl After all, *Asp, Phe, CoA acetyl CoA Tyr Propionyl leads to CoA *Glu oxaloacaetate Arg,to leads Ile, Met, *Gln, GNG… Val His, Pro42  Catabolism: C-skeletons Memorizing classifications Ketogenic only: the two “L’s” – lysine and leucine Both ketogenic and glucogenic: can you “fit” (FITTT) these 5 aa’s into your brain next? FITTT – phenylalanine (‘fenylalanine’, F), isoleucine (I), and all aa’s that start with “T” = tyrosine, threonine (T), tryptophan Any that you haven’t Review Material Amino Acids: Acid/Base review What is the pKa range for: An amino group An acid group Based on your answer above: Draw a carboxylic acid at pH = 7 Draw an amino group at pH = 7 Relate the above to the statements: “all amino acids are zwitterions at pH=7” Amino acids are amphoteric Amino acids Match the following amino acids with the structures below: Cys, Glu, Asn, Pro, Met, Ser, Val, Trp, Gly, His Amino acids Match the following amino acids with the appropriate description (one aa won’t be used): Asp Never found in an alpha helix Cys Essential amino acid in PKU His Main component of Glutathione Gln R-group contains a carboxylic acid Phe R-group contains an amido group Pro Can be decarboxylated to create a Ser molecule that mediates allergic Tyr responses Can be converted to Cys with the help of B6 Amino Acids Match the following amino acids with the correct keto acid: Amino acids: alanine, aspartate, glutamate Keto acids: alpha ketoglutarate, oxaloacetate, pyruvate Amino Acids Fill in the blanks: The urea cycle begins when ornithine combines with (A) to make (B). (A) has a nitrogen that comes from either the ( C ) cycle or the glutamine synthase reaction. Urea has two N’s. One comes from (A) as described above. The other comes from (D). The urea cycle only happens in the (E), as this is the only tissue that has the enzyme (F). Amino Acids Classify the following amino acids as either G (glucogenic only), K (ketogenic only), or GK (both gluco- and keto- genic): Iso Trp Asp Phe Lys His Leu Vitamins Name the coenzyme form of B6 and B9. Match each biochemical function on the left to the correct pathway on the right, and label each as belonging to either B6 or B9: Conversion of ser to gly One-carbon transfer Conversion of ser to cys Transamination Conversion of ala to Transulfhydration pyruvate