Question

The octapeptide angiotensin II has the sequence Asp-Arg-Val-Tyr-Ile-His- ProPhe. What fragments would result if angiotensin II were cleaved with trypsin? With chymotrypsin?

Short answer

Trypsin: Asp-Arg, Val-Tyr-Ile-His-Pro-Phe. Chymotrypsin: Asp-Arg-Val-Tyr, Ile-His-Pro, Phe.

Step-by-step solution

Understanding Trypsin Cleavage

Trypsin is an enzyme that specifically cleaves peptide bonds at the carboxyl side of lysine (Lys, K) and arginine (Arg, R). In the sequence Asp-Arg-Val-Tyr-Ile-His-Pro-Phe, trypsin will cleave at Arg, resulting in two fragments.

Trypsin Cleavage Sites

The sequence Asp-Arg-Val-Tyr-Ile-His-Pro-Phe has an Arg at position 2. Therefore, cleaving after Arg by trypsin results in the fragments: Asp-Arg and Val-Tyr-Ile-His-Pro-Phe.

Understanding Chymotrypsin Cleavage

Chymotrypsin cleaves peptide bonds following aromatic amino acids such as phenylalanine (Phe, F), tyrosine (Tyr, Y), and tryptophan (Trp, W). In the provided sequence, chymotrypsin will potentially cleave after Tyr and Phe.

Chymotrypsin Cleavage Sites

In the sequence: Asp-Arg-Val-Tyr-Ile-His-Pro-Phe, the aromatic residues Tyr and Phe are at positions 4 and 8. Chymotrypsin will cleave after these residues, resulting in fragments: Asp-Arg-Val-Tyr, Ile-His-Pro, and Phe.

Key concepts

Angiotensin II: A Key Peptide in Blood Pressure Regulation

Angiotensin II is a small peptide consisting of eight amino acids. It plays a crucial role in the body by regulating blood pressure and fluid balance. This peptide is a part of the renin-angiotensin system, which helps control the constriction of blood vessels. This, in turn, influences how much blood your heart pumps and ultimately your blood pressure levels. When you hear about hypertension, or high blood pressure, angiotensin II often comes into discussion due to its vasoconstrictive properties. Its sequence, Asp-Arg-Val-Tyr-Ile-His-Pro-Phe, can be broken down to understand how enzymes interact with such molecules.

Trypsin: Specific Cleavage of Peptide Bonds

Trypsin is a digestive enzyme that comes into action primarily in the small intestine. It has a specific preference for cutting peptide bonds at the carboxyl side of lysine (Lys, K) and arginine (Arg, R) amino acids. This makes trypsin important for digesting proteins effectively. In the context of angiotensin II, which includes the sequence Asp-Arg, trypsin will cleave just after Arg. This cleavage results in two separate peptide fragments: Asp-Arg and Val-Tyr-Ile-His-Pro-Phe. Understanding trypsin’s selective process helps in studying enzymatic activities related to protein digestion and molecular biology research.

Chymotrypsin: Cleaving Aromatic Residues

Chymotrypsin is another enzyme often discussed alongside trypsin. Unlike trypsin, it targets peptide bonds following aromatic amino acids, such as phenylalanine (Phe, F), tyrosine (Tyr, Y), and tryptophan (Trp, W). This specific action makes it crucial for breaking down a variety of proteins into smaller peptides. In angiotensin II, the amino acids Tyr and Phe serve as cleavage points for chymotrypsin. The enzyme cuts the bonds after these residues, resulting in fragments: Asp-Arg-Val-Tyr, Ile-His-Pro, and Phe. Chymotrypsin's unique specificity is vital for understanding protein digestion, peptide analysis, and even certain pharmaceutical applications.

Peptide Bonds: The Backbone of Proteins

Peptide bonds link amino acids together to form the backbone of peptides and proteins. They are formed through a condensation reaction between the carboxyl group of one amino acid and the amino group of another. These bonds are stable under physiological conditions but can be broken by specific enzymes like trypsin and chymotrypsin, which cleave them at designated sites. Understanding peptide bonds is fundamental for anyone studying biochemistry, as they form the primary structure of proteins and peptides like angiotensin II.

Amino Acids: Building Blocks of Life

Amino acids are organic compounds that combine to form proteins, which are essential for all living organisms. Each amino acid contains an amino group, a carboxyl group, and a unique side chain (R group) that distinguishes it from others. With 20 different amino acids available in biology, they have varying properties and functions. Some are polar, others non-polar, and some carry positive or negative charges. This diversity allows proteins to have complex structures and functions. In our example, the sequence of amino acids in angiotensin II provides a specific and important function related to blood pressure regulation. Understanding the properties and roles of each amino acid is significant in fields like nutrition, medicine, and genetics.