Problem 58 - General Chemistry: Principles and Modern Applications

Question

Bradykinin is a nonapeptide obtained by the partial hydrolysis of blood serum protein. It causes a lowering of blood pressure and an increase in capillary permeability. Complete hydrolysis of bradykinin yields three proline (Pro), two arginine (Arg), two phenylalanine (Phe), one glycine (Gly), and one serine (Ser) amino acid units. The N-terminal and C-terminal units are both arginine (Arg). In a hypothetical experiment, partial hydrolysis and sequence proof reveals the following fragments: Gly-Phe-Ser-Pro; Pro-Phe-Arg; Ser-Pro-Phe; Pro-Pro-Gly; Pro-Gly-Phe; Arg-Pro-Pro; Phe-Arg. Deduce the sequence of amino acid units in bradykinin.

Step-by-Step Solution

Answer

The sequence of amino acids in bradykinin is Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg.

Step 1: Identify the termini

First identify the N-terminal and C-terminal positions. As the exercise indicates, both the N-terminal and C-terminal units are arginine (Arg). It therefore means that our sequence will start and end with Arg.

Step 2: Start piecing together fragments

Next, start matching the sequence of amino acids in the fragments. Always ensure that the sequence fits together correctly. For example, Pro-Phe-Arg fits perfectly before Arg-Pro-Pro because Phe-Arg can connect to Arg-Pro-Pro to form Phe-Arg-Pro-Pro, and so on.

Step 3: Continue the sequence

The next piece in the sequence after Arg-Pro-Pro is Pro-Gly-Phe, this fragment can fit after Pro-Pro without overlap to form Arg-Pro-Pro-Gly-Phe.

Step 4: Add remaining fragments

Continue to add each fragment making sure there is no overlap. If you follow this methodology, you end up with a complete sequence of Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg. This matches with our initial terminal units and thus is the correct sequence of amino acids in bradykinin.

Key Concepts

Biochemistry and Amino Acid Sequence Determination

Biochemistry lies at the intersection of biology and chemistry, exploring the molecular mechanisms that underpin living organisms. In particular, the study of proteins—large molecules made up of amino acids—plays a central role in understanding biological processes.

Proteins perform vital functions, and the specific order of amino acids, known as the amino acid sequence, determines a protein's structure and function. Determining the amino acid sequence is a crucial step in biochemistry research because it provides insight into the protein's activity and interaction with other molecules.

For students tackling such problems, it's integral to understand the basic principle that the amino acid sequence determines a protein's characteristics. The exercise on deciphering the bradykinin sequence is a prime example, showcasing how biochemists deduce structure from experimental data, a vital skill in the discipline.

Proteins Hydrolysis in Understanding Protein Composition

Proteins are polymers of amino acids linked by peptide bonds, and hydrolysis is the process used to break these bonds. During protein hydrolysis, water molecules are added, cleaving the peptide bonds and releasing individual amino acids or smaller peptides.

Understanding proteins hydrolysis is essential for biochemists, as it allows them to determine the protein's composition by analyzing the resulting amino acids. For students, recognizing that complete hydrolysis yields the basic building blocks of proteins—amino acids—is the key takeaway. Meanwhile, partial hydrolysis, as used in the bradykinin exercise, helps to identify sequences within the protein by producing smaller peptide fragments. This analytical approach is foundational to piecing together protein structure.

Peptides Sequencing Techniques

Peptide sequencing involves the identification of the order of amino acids in a peptide, a short chain of amino acids. Step-by-step fragmentation, like in the exercise with bradykinin, is a proven strategy for deducing the sequence.

For a correct approach, fragments obtained from partial hydrolysis must be logically pieced together, ensuring they align with known information about the protein, such as terminal amino acids. The strategy of overlapping fragments, as used in the solution, is fundamental in sequencing work. Additionally, techniques such as Edman degradation or mass spectrometry may be employed in real-world scenarios to determine sequences more complex than bradykinin efficiently. However, the underlying concepts of careful analysis and pattern recognition remain consistent.

The Structure of Bradykinin

Bradykinin is a nonapeptide, meaning it consists of nine amino acids. Its biological role involves causing vasodilation, which can affect blood pressure and capillary permeability. The structure of bradykinin is crucial for its function; incorrect sequencing could lead to a loss of biological activity.

In our textbook exercise, understanding the biochemical properties of bradykinin, such as its specific amino acids and their counts, is fundamental. The sequence provided, Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg, reflects the correct arrangement of amino acids in bradykinin, ensuring that it can perform its role in the body. Learning how its structure directly impacts its function is a cornerstone concept of biochemistry that students must grasp.