Chapter_24 - P1: PCX JWDD052-24 JWDD052-Solomons-v3...

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P1: PCX Printer: Hamilton JWDD052-24 JWDD052-Solomons-v3 May 4, 2007 14:20 24 AMINO ACIDS AND PROTEINS SOLUTIONS TO PROBLEMS 24.1 (a) (b) HO OH O O NH 3 + (c) predominates at the isoelectric point rather than because of the acid-strengthening inductive effect of the α -aminium group. HO O O O NH 3 + O OH O O NH 3 + O O O O NH 2 (d) Since glutamic acid is a dicarboxylic acid, acid must be added (i.e., the pH must be made lower) to suppress the ionization of the second carboxyl group and thus achieve the isoelectric point. Glutamine, with only one carboxyl group, is similar to glycine or phenylalanine and has its isoelectric point at a higher pH. 24.2 The conjugate acid is highly stabilized by resonance. HA NH NH 2 N R H NH 2 NH 2 N R + H NH 2 NH 2 N R + H NH 2 NH 2 N R + H 557
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P1: PCX Printer: Hamilton JWDD052-24 JWDD052-Solomons-v3 May 4, 2007 14:20 558 AMINO ACIDS AND PROTEINS 24.3 NK (a) + O O Br N O O O O EtO EtO EtO EtONa NaOH heat HCl heat OEt O O Br N O O O O OEt OEt O O O O O O OH O OH O DL -Leucine + + CO 2 O NH 3 + O (b) EtONa CH 3 I HCl heat ++ CO 2 NaOH heat N O OEt OEt O O O O NH 3 + O N O O O OEt OEt O O O O O O O H N H N O OH O OH DL -Alanine O O
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P1: PCX Printer: Hamilton JWDD052-24 JWDD052-Solomons-v3 May 4, 2007 14:20 AMINO ACIDS AND PROTEINS 559 (c) EtONa NaOH heat HCl heat N O OEt OEt O O O C 6 H 5 C 6 H 5 C 6 H 5 C 6 H 5 Br N O O O + + CO 2 OEt OEt O O O O O O N H DL -Phenylalanine O NH 3 + O O OH O OH O O 24.4 (a) O H Phenylacetaldehyde NH 2 CN DL -Phenylalanine DL -Methionine NH 3 + O O NH 3 HCN base NH 3 HCN H 3 O + H O H CH 3 S O H 3 O + NH 2 CH 3 S CN NH 3 + CH 3 S O O (b) CH 3 SH + 24.5 Because of the presence of an electron-withdrawing 2,4-dinitrophenyl group, the labeled amino acid is relatively nonbasic and is, therefore, insoluble in dilute aqueous acid. The other amino acids (those that are not labeled) dissolve in dilute aqueous acid.
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P1: PCX Printer: Hamilton JWDD052-24 JWDD052-Solomons-v3 May 4, 2007 14:20 560 AMINO ACIDS AND PROTEINS 24.6 H 3 O + heat N H VAG NO 2 O 2 N HCO 3 F H 3 N + O (a) (b) O O O N H N H O 2 N NO 2 O O O O N H N H OH + O 2 N NO 2 NH 3 + H 3 N + O N H Labeled valine (separate and identify) Alanine Glycine OH O 2 N NO 2 O + N H α -Labeled valine ε -Labeled lysine O O + O O O 2 N NO 2 NH 3 + N H O O Glycine + H 3 N + O O 24.7 N + OH N H O H 2 N SCH 3 O O O HN NH 2 N H H C Phenyl isothiocyanate MIR S N
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P1: PCX Printer: Hamilton JWDD052-24 JWDD052-Solomons-v3 May 4, 2007 14:20 AMINO ACIDS AND PROTEINS 561 H 3 O + N H O O S N H N H N H Phenylthiohydantoin derived from isoleucine N (1) C S (2) H 3 O + O O H 2 N NH + N S O + Phenylthiohydantoin derived from methionine H 2 N O O O N H N S O SCH 3 HN NH 2 H CH 3 S N HN NH 3 + H N HN NH 2 H N O O 24.8 (a) Two structures are possible with the sequence ECG. Glutamic acid may be linked to cysteine through its α -carboxyl group.
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This note was uploaded on 09/10/2008 for the course CHE 321 taught by Professor Fowler/sampson during the Spring '08 term at SUNY Stony Brook.

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Chapter_24 - P1: PCX JWDD052-24 JWDD052-Solomons-v3...

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