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Chapter 32: Problem 738

A pentapeptide on complete hydrolysis yields 3 moles of glycine, 1 mole of alanine, and 1 mole of phenylalanine. Among the products of partial hydrolysis are found \(\mathrm{H} \cdot \mathrm{Ala} \cdot \mathrm{Gly} \cdot \mathrm{OH}\) and \(\mathrm{H} \cdot \mathrm{Gly} \cdot \mathrm{Ala} \cdot \mathrm{OH}\). What structures are possible for this substance on the basis of its giving no nitrogen in the Van Slyke determination?

Short Answer

Expert verified
Considering the given conditions, there are two possible structures for the pentapeptide: 1. Gly-Gly-Ala-Gly-Phe 2. Gly-Gly-Gly-Ala-Phe These structures fit the requirements of no nitrogen detection in the Van Slyke determination and account for all amino acids and partial hydrolysis products given in the exercise.

Step by step solution

01

Understand the given information

We know there are a total of 5 amino acids in the pentapeptide - 3 Gly, 1 Ala, and 1 Phe. Two partial hydrolysis products are H·Ala·Gly·OH and H·Gly·Ala·OH. The substance doesn't produce any nitrogen in the Van Slyke determination, which means that there is no free amino group (-NH_2) at the N-terminal of the peptide.
02

Determine the N-terminal amino acid of the pentapeptide

Since no nitrogen is detected in the Van Slyke determination, the N-terminal amino acid can't have a free -NH_2 group. This suggests that the N-terminal amino acid must be one of the 3 moles of Glycine as it's the only amino acid that can create a residue without a free -NH_2 group when it forms a peptide bond with another Glycine. In other words, the N-terminal end must be Gly-Gly.
03

Formulate the possible structures considering the partial hydrolysis products

Since we know two partial hydrolysis products: H·Ala·Gly·OH and H·Gly·Ala·OH, it indicates that Gly and Ala residues can interchange positions in the middle of the peptide chain, while preserving the N-terminal Gly-Gly bond. Therefore, consider the following order of amino acids in the peptide chain: 1. Gly-Gly-Ala-Gly-Phe 2. Gly-Gly-Gly-Ala-Phe Both of these possible structures start with the N-terminal Gly-Gly and incorporate all 3 Gly residues, as well as 1 Ala and 1 Phe residue.
04

Provide the final possible pentapeptide structures

Considering the conditions given in the exercise, there are two possible structures for the pentapeptide: 1. Gly-Gly-Ala-Gly-Phe 2. Gly-Gly-Gly-Ala-Phe Note that these structures fit the requirements of no nitrogen detection in the Van Slyke determination and account for all amino acids and partial hydrolysis products given in the exercise.

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Most popular questions from this chapter

The complete structure of Gramicidin \(\mathrm{S}\), a polypeptide with antibiotic properties, has been worked out as follows: (a) Analysis of the hydrolysis products gave an empirical formula of Leu, Orn, Phe, Pro, Val. (Ornithine, Orn, is a rare amino acid of formula \(\left.{ }^{+} \mathrm{H}_{3} \mathrm{NCH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}\left(\mathrm{NH}_{2}\right) \mathrm{COO}^{-} .\right)\) It is interesting that the phenylalanine has the unusual D-configuration. Measurement of the molecular weight gave an approximate value of \(1300 .\) On this basis, what is the molecular formula of Gramicidin \(\mathrm{S} ?\) (b) Analysis for the C-terminal residue was negative; analysis for the N-terminal residue using DNFB yielded only DNP-NHCH \(_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}\left(\mathrm{N}^{+} \mathrm{H}_{3}\right) \mathrm{COO}^{-}\). What structural feature must the peptide chain possess? (c) Partial hydrolysis of Gramicidin \(\mathrm{S}\) gave the following di- and tripeptides: Leu.Phe Phe.Pro Phe.Pro.Val Val.Orn.Leu \(\begin{array}{lll}\text { Orn.Leu } & \text { Val.Orn } & \text { Pro. Val.Orn }\end{array}\) What is the structure of Gramicidin \(\mathrm{S} ?\)

Hemoglobin, the protein responsible for carrying oxygen from the lungs to the body tissues, contains \(0.355\) per cent iron. Hydrolysis of \(100 \mathrm{~g}\) of hemoglobin gives \(1.48 \mathrm{~g}\) of tryptphan; calculate the minimum molecular weight of hemoglobin which is consistent with these results.

Of what importance are proteins to biological svstems?

Show how each of the following substances can be synthesized starting with the individual amino acids. (a) glycylalanylcysteine (b) \(\mathrm{HO}_{2} \mathrm{C}\left(\mathrm{CH}_{2}\right)_{2} \mathrm{CH}\left(\mathrm{NH}_{2}\right) \mathrm{CONHCH}_{2} \mathrm{CO}_{2} \mathrm{H}\) (c) glutamine from glutamic acid

In quite alkaline solution, an amino acid contains two basic groups, \(-\mathrm{NH}_{2}\) and \(-\mathrm{COO}^{-}\). Which is the more basic? To which group will a proton preferentially go as acid is added to the solution? What will the product be?
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