Question

A tetrapeptide on complete hydrolysis yielded Val, Leu, Tyr, and Glu. The reaction on tetra peptide with DNFB reagent gave DNP derivative of Leucine. Selective hydrolysis of tetrapeptide resulted in the formation of peptides as Val-Glu, Leu-Tyr-Val, Tyr-Val-Glu, and Leu-Tyr. Identify the tetrapeptide.

Short answer

The tetrapeptide sequence is Leu-Tyr-Val-Glu.

Step-by-step solution

Understand the Problem

We are given a tetrapeptide that on complete hydrolysis breaks into Valine (Val), Leucine (Leu), Tyrosine (Tyr), and Glutamic Acid (Glu). The DNP (dinitrophenyl) derivative points to the N-terminus being Leucine. We need to find the sequence of the tetrapeptide.

Use DNFB Reaction Information

The reaction with DNFB indicates that Leucine forms the DNP derivative, which means Leucine is the N-terminal amino acid in the sequence.

Analyze Selective Hydrolysis Results

From the selective hydrolysis, we found some peptide fragments: Val-Glu, Leu-Tyr-Val, Tyr-Val-Glu, and Leu-Tyr. Analyze these fragments to gain insights about the peptide bonds and order. - Leu-Tyr-Val and Leu-Tyr share a common sequence, suggesting this segment. - Tyr-Val-Glu and Val-Glu share another common sequence, suggesting these segments.

Arrange the Sequence

Using the identified sequences and the common peptide patterns, arrange them: starting with Leu (from Step 2), the sequence can fit as Leu-Tyr-Val-Glu. The fragments support each other's continuity with Leu-Tyr and Tyr-Val-Glu.

Key concepts

Amino Acid Hydrolysis

Amino acid hydrolysis is a crucial process in determining the composition of peptide or protein sequences. During hydrolysis, peptide bonds within proteins are broken down into individual amino acids. This process involves the use of strong acids or bases to sever the bonds between amino acids.
In the exercise, the tetrapeptide undergoes complete hydrolysis, yielding the amino acids Valine (Val), Leucine (Leu), Tyrosine (Tyr), and Glutamic Acid (Glu). This result tells us that these four amino acids are the components of the original tetrapeptide.

• Complete Hydrolysis: It means breaking down the entire sequence into all its amino acids.
• Significance: Knowing the amino acids present helps in further analysis of the sequence.

DNFB Reagent

DNFB, or 1-fluoro-2,4-dinitrobenzene, is a chemical reagent used to help identify the N-terminal amino acid in a peptide sequence. DNFB reacts with the N-terminal amino acid to form a DNP derivative.
In the given exercise, when the tetrapeptide is treated with DNFB, Leucine forms a DNP derivative. This reaction confirms that Leucine is the amino acid at the N-terminus of the peptide.

• Purpose: Identify the first amino acid in the peptide chain.
• Reaction: Forms a stable derivative with the N-terminal amino acid.
• Outcome: Confirming Leucine is positioned at the start of the sequence.

Peptide Bond Analysis

Peptide bond analysis is a method to study the linkages between amino acids in peptides or proteins. By understanding which peptide bonds are cleaved during experiments like selective hydrolysis, we can determine the order of amino acids in a peptide chain.
In this exercise, analyzing the fragments produced by selective hydrolysis helps to piece together the tetrapeptide sequence. Each fragment provides clues about the neighboring amino acids.

• Peptide Fragments: Short segments resulting from bond cleavage.
• Fragment Analysis: Understand overlapping regions to determine sequence adjacency.
• Continuity: Fragments like Val-Glu and Leu-Tyr suggest bonds and order.

Selective Hydrolysis

Selective hydrolysis breaks specific peptide bonds under controlled conditions, providing insight into the sequence of peptides. It results in peptide fragments that reveal detailed information about the composition and order within the peptide.
In the exercise, selective hydrolysis yields fragments such as Val-Glu, Leu-Tyr-Val, Tyr-Val-Glu, and Leu-Tyr. When we look at these fragments:

• Common Sequences: Overlapping regions like Leu-Tyr-Val and Leu-Tyr help identify part of the sequence.
• Structural Insights: Combining all fragments shows the logical order of the sequence as Leu-Tyr-Val-Glu.
• Application: Helps in determining the order by combining known overlaps.