analysis of amino acid and proteins - 4

analysis of amino acid and proteins - 4 - 4-1Cell and...

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Unformatted text preview: 4-1Cell and Molecular Biology (Biol. Chem. 410A)Lecture #4Harry R. Matthews, Ph.D.October 1, 1996Analysis of Amino Acids and ProteinsClinical correlations:phenylketonuriacystinuriaHartnups diseaseFanconis syndromediabetes insipidusLearning objectives:amino acid analysisprotein purificationprotein sequencingEdman degradationprotein:protein interactionspeptide synthesisOptional reading:Stryer IV:Chapter 3Alberts et al.:3rd Ed., Chapter 4, pp. 166-174.he following 4 aspects of amino acid and protein analysis have clinical importance:T1.amino acid analysis (of biological fluids such as urine or of protein hydrolyzates)2.protein purification (for example, as a preliminary to further study of possibly defective proteins)3.protein sequence studies (for example, in hemoglobinopathies or drugs derived from recombinant DNA)4.peptide synthesis (potential for drug production)Amino acid analysis can often diagnose a defect in amino acid transport. Here are 3 ex-amples:cystinuriagenetic defect in membrane transport sys-tem for cysteine, lysine, arginine and or-nithine in epithelial cellssymptoms: renal stones due to cysteine precipitation in the kidneyHartnup diseasegenetic defect in transport of neutral amino acidssymptoms: pellagra-like rash (like Trp de-ficiency); cerebellar ataxia (from indole produced by bacterial degradation of ex-cess Trp in the gut)Fanconis syndromegeneralized amino acid uria correlated with hypophosphatemia and high excre-tion of glucoseFigure 41. Phenylalanine hy-droxylase.A significant portion of people are born with a defect in the enzyme, phenylalanine hydroxylase. This enzyme is required for the 4-2conversion of phenylalanine to tyrosine (Fig-ure 41) and in the absence of phenylalanine hydroxylase, phenylalanine from the diet ac-cumulates to high levels and causes brain damage during early development. If detected at birth or just after, PKU can be treated by careful control of phenylalanine in the diet.A number of peptides act as hormones or extracellular signal molecules. Peptide syn-thesis can be used to synthesize such mo-lecules and to make alterations that improve their value as drugs. For example, a modified vasopressin, 1-desamino-8-D-arginine vaso-pressin is used to treat diabetes insipidus. It degrades slowly and does not increase blood pressure.Amino Acid Analysis.Amino acids can be released from proteins by heating to 110 C in 6N HCl for about 24 hr. The procedure destroys Trp and converts Gln and Asn to Glu and Asp but it is widely used. The different amino acids are then separated by ion-exchange chromatography on a sulfon-ated polystyrene resin. Each amino acid is ated polystyrene resin....
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