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CONVERSION OF AMINO ACIDS TO SPECIALIZED PRODUCTS Jana Novotn nitrogen atom of amino acids is a primary source for many nitrogenous compounds: Heme Purines and pyrimidines Hormones Neurotransmitters Biologically active peptides

Glycine Glycine is used for heme, purine and creatin synthesis carbon and nitrogen atoms of glycine are used for synthesis of porphyrine, prosthetic group of heme. Take over: Synthesis of heme carbon and nitrogen athoms of glycine are used for synthesis of porphyrine, prosthetic group of heme. 1. Condensation of 1 glycine and 1 succinylCoA by the pyridoxal phosphate-containing enzyme, -aminolevulinic acid aminolevulinic acid

synthase (ALA synthase) in mitochondria. Take over: 2. -aminolevulinic acid (ALA) is transported to the cytosol. 3. Porfobilinogen synthase (ALA dehydratase) dimerizes 2 molecules of ALA to produce the pyrrole ring compound porphobilinogen. precursor for porphyrine synthesis Take over: Glycine is incorporated intact

as constituent of purines. Synthesis of Creatine and Creatinine Creatine nitrogenous organic acid - helps to supply energy to muscle. Creatine by way of conversion to and from phosphocreatine is present and functions in all vertebrates as energy buffer system. Kkeeps the ATP/ADP ratio high at subcellular places where ATP is needed. The amount of creatinine produced is related to muscle mass. The level of creatinine excretion (clearance rate) is a measure of renal function.

Take over Synthesis of glutathione (GSH) 1. 2. 3. 4. Glutathione serves as a reductant; is conjugated to drugs to make them more water soluble (detoxification). Reduces peroxides formed during oxygen transport. The resulting oxidized form of GSH consists of two molecules disulfide bonded together (abbreviated GSSG). Is involved in amino acid transport across cell membranes (the -glutamyl cycleglutamyl cycle).

Serves as a cofactor for some enzymatic reactions and as an aid in the rearrangement of protein disulfide bonds. Take over: Tyrosine The majority of tyrosine that does not get incorporated into proteins: is catabolized for energy production. is conversion to the catecholamines. The catecholamine neurotransmitters are dopamine norepinephrine, and epinephrine. Norepinephrine is the principal neurotransmitter of sympathetic postganglionic endings. Catecholamines are stored in synaptic knobs of neurons

that secrete it. Tyrosine is transported into catecholamine-secreting neurons and adrenal medullary cells where catecholamine synthesis takes place. ynthesis of the Catecholamines from Tyrosine 1. 2. 3. 4. 5. Tyrosine hydroxylase

requires tetrahydrobiopterin as cofactor. The hydroxylation reaction generates DOPA. (3,4dihydrophenylalanine) DOPA decarboxylase converts DOPA to dopamine. Dopamine b-glutamyl cyclehydroxylase converts dopamine to norepinephrine. Phenylethanolamine N-glutamyl cycle methyltransferase converts norepinephrine to epinephrine.

Take over: -aminobutyric acid (GABA) Inhibitory neurotransmitter (CNS). Directly regulates muscle tone. Its lack leads to convulsions, epilepsia. Involved in mechanism of memory. Tryptopha

n Tryptopan serves as the precursor for the synthesis of serotonin and melatonin Hydroxylation reaction (tryptophan-5-monooxygenase) Decarboxylation (aromatic Lamino acid decarboxylase) Acetylation (serotonin N-acetylase) Conversion to melatonin

(hydroxyindole-Omethyltransferase). Take of textbook: D. L. Nelson, M. M. Cox: Lehninger Principle of Biochemistry. Fourt Deition. Serotonin and melatonin Serotonin is present at highest concentrations in platelets and in the gastrointestinal tract. Lesser amounts are found in the brain and the retina. Serotonin containing neurons have their cell bodies in the midline raphe nuclei of the brain stem. Proportions of neurons are projected to the hypothalamus, the limbic system, the neocortex and the spinal cord. The released serotonin is recaptured by an active reuptake mechanism.

Antidepressant, Prozac is to inhibit this reuptake process. Synthesis and secretion of melatonin increases during the dark period of the day. Concentration maintained at a low level during daylight hours. Polyamine Biosynthesis 1. 2. Conversion of arginine to ornithine. Ornithine to putrescine (ornithine decarboxylase). 3. Putrescine to spermidine (spermidine

synthase, putrescine aminotransferase). 4. Spermidine to spermine(Spermidine aminotranspherase). SAM s-adenosyl methionine is donor of methyl group Polyamines are highly cationic and tend to bind nucleic acids with high affinity. Important participants in DNA

synthesis, or in the regulation of that process. Important modulators of a variety of ion channels (potassium channel) Growth factors in both eucaryotic and procaryotic cells. Take over: Histidine Carnosine is the dipeptide of the amino acids -alanine and histidine. Carnosine is highly concentrated in muscle and brain tissues.

Scavenger of ROS (radical oxygen species). Protection of the peroxidation of cell. Membrane fatty acids during oxidative stress. Possibly improving Alzheimers disease through inhibition of growing an aggregates of b-amiloid proteins in Carnosine Histamine Histamine is derived from the

decarboxylation of the amino acid histidine. Biogenic amine regulating physiological function in the gut and acting as a neurotransmitter. Causes several allergic symptoms. 1) It contributes to an inflammatory response. 2) It causes constriction of smooth muscle. 3) Is cause second type of allergic response (one of the major causes for asthma)

Nitric Oxide NO Nitric oxide (NO) is produced by vascular endothelium and smooth muscle, cardiac muscle, and many other cell types. The substrate for NO is L-arginine that is transported into the cell. Nitric oxide serves many important functions: Vasodilation (ligand mediated and flow dependent) Inhibition of vasoconstrictor influences (e.g.,

inhibits angiotensin II and sympathetic vasoconstriction) Inhibition of platelet adhesion to the vascular endothelium (anti-thrombotic) Inhibition of leukocyte adhesion to vascular endothelium (anti-inflammatory) Antiproliferative action (e.g., inhibits smooth muscle hyperplasia following vascular injury) Useful webe sites

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