Protein and Amino Acid Metabolism

• These products directly enter the pathways of intermediary metabolism, resulting either in the synthesis of Glucose or lipids, or in the production of energy through their oxidation to CO2 and H2O by the citric acid cycle.
• Amino acids whose catabolism yields Pyruvate or one of the Intermediates of the citric acid cycle are termed glucogenic or glycogenic.
• Ornithine decarboxylase (ODC) is a PLP-dependent enzyme that catalyzes the decarboxylation of SAM to form putrescine.
• Glucogenic amino acids can give rise to the net formation of glucose or glycogen in the liver and glycogen in the muscle.
• Cysteine is the precursor of taurin.
• Important products derived from amino acids include Heme, Purines, Pyrimidines, Hormones, Neurotransmitters and Biologically active peptides.
• Methionin is the precursor of carnitine, spermin, spermidin, ansserin.
• Amino acids whose catabolism yields either Acetyl CoA or Acetoacetyl CoA are termed ketogenic.
• Spermine synthase catalyzes the formation of spermine from decarboxylated SAM and 5’-methylthioadenosine.
• The carbon skeletons of amino acids are converted to Pyruvate, Acetyl-CoA, Acetoacetyl-CoA, Oxaloacetate, Alpha-ketoglutarate, Fumarate, Succinyl-CoA.
• Glutamate is the precursor of glutatyon and GABA.
• The catabolism of amino acids found in the proteins involves the removal of alpha amino groups, followed by the breakdown of the resulting carbon skeletons.
• Histidine is the precursor of histamine, carnosine, ergothioneine, anserin, and homocarnosine.
• NH3 + + O2 CCH2 CH2 CHCO2 - NH3 + O2 CCH2 CH2 CH2 Glutamate Gamma-aminobutyrate (GABA) Glutamate decarboxylase CO2.
• Ornithine is a product of the urea cycle.
• Spermidine synthase catalyzes the formation of spermidine from decarboxylated SAM and 5’-methylthioadenosine.
• Examples of organic acidemias include Glutaric acidemia type I, Isovaleric acidemia, Methylmalonic acidemia, and Propionic acidemia.
• The metabolism of amino acids involves biosynthesis, catabolism, conversion to specialized products, and the conversion of amino acids to intermediates of metabolism.
• Plasma and urinary levels of leucine, isoleucine, valine, α-keto acids, and α-hydroxy acids (reduced α-keto acids) are elevated in maple syrup urine disease.
• The abnormal metabolism in phenylketonuric subjects involves pathway c.
• Phenylalanine is first converted to tyrosine in the body and Hyperphenylalaninemias arise from defects in phenylalanine hydroxylase itself (type I, classic phenylketonuria or PKU), in dihydrobiopterin reductase (types II and III), or in dihydrobiopterin biosynthesis (types IV and V).
• Early diagnosis of maple syrup urine disease, especially prior to 1 week of age, employs enzymatic analysis.
• Phenylketonuria (PKU) is the most common clinically encountered inborn error of amino acid metabolism and is characterized by Hyperphenylalaninemia.
• Maple syrup urine disease is characterized by the odor of urine in maple syrup urine disease (branched-chain ketonuria) and involves the -keto acid decarboxylase complex.
• Phenylalanine is found in dietary sources, particularly plant proteins.
• Aminoacidopathies are conditions where the parent amino acid accumulates in excess in blood and spills over into urine.
• Examples of aminoacidopathies include Phenylketonuria (PKU), Maple syrup urine disease, Homocystinuria, and Tyrosinemia type I.
• Agents, thought to be responsible for mental retardation in phenylketonuric subjects, include phenylalanine, dietary sources of phenylalanine, and products of phenylalanine catabolism.
• Prompt replacement of dietary protein by an amino acid mixture that lacks leucine, isoleucine, and valine averts brain damage and early mortality in maple syrup urine disease.
• Organic acidemias are conditions where products in the catabolic pathways of certain amino acids accumulate.
• The normal metabolism of phenylalanine involves pathways a and b.
• A diet low in phenylalanine can prevent the mental retardation of PKU.
• Ammonia is partly lost in the feces, and is partly reabsorbed into the blood.
• The metabolism of amino acids involves biosynthesis, catabolism, conversion to specialized products, and effects in amino acid metabolism.
• Protein turnover occurs in all forms of life.
• Amino acids synthesized from intermediates of metabolism include Alanine, Aspartate, Glutamate, which are synthesized by transfer of an amino group to the α-keto acids.
• Most proteins in the body are constantly being synthesized and then degraded, permitting the removal of abnormal or unneeded proteins.
• Nonessential amino acids are synthesized from intermediates of metabolism or, as in the case of tyrosine and cysteine, from essential amino acids.
• Glutamine, Asparagine, and Serine are synthesized from Glutamate, Aspartate, and 3-phosphoglycerate respectively.
• Each day humans turnover 1-2% of their total body protein, principally muscle protein.