Peptides: Why Do We Need Them?

Peptides, like proteins, are molecules formed by the binding of different amino acids; these amino acids are linked by bonds called peptides. Peptides have many functions in the organism, just as proteins can have them. These molecules are part of many metabolic processes. Generally, when many amino acids (more than 100) are joined together, very large molecules are formed, and these are what we call proteins. The smaller molecules or those in which fewer amino acids have been merged are what we know as peptides. They have less mass and are therefore smaller. Depending on the type of amino acids that are joined and the molecules that are formed, larger or smaller, they will be different and will have different functions. That is why we find so many types and names. We call them polypeptides when more than ten amino acids are joining together. We know them as oligopeptides when the number of amino acids is less than 10, and from there, we see the known ones or at least those that sound more familiar: hexapeptides (6 amino acids), pentapeptides (5), tetrapeptides (4), tripeptides (3), etc.

In the body, peptides have very different functions. They can be from hormones, such as insulin or glucagon, to substances that can become antimicrobial agents with the ability to alter the development of some microbes.

Some of their functions are: 

1. Stimulation Vessel: The most powerful hypertensive agent known as angiotensin II, an octapeptide that is formed by the hydrolysis of a precursor protein called angiotensinogen, which has no vasopressor activity. On the other hand, other peptides are hypotensive agents (they have vasodilatory activity). One of the best known is bradykinin, a biologically active peptide that is released from damaged tissues as a signal of pain and might act as a neurotransmitter.

2. Hormones: Hormones are chemical signals that exert their action on organs and tissues located far from the site where they have been synthesized. Many hormones have a peptide structure, for example:

• Oxytocin: Non-peptide secreted by the pituitary gland It causes the uterine contraction and the secretion of milk by the mammary gland, facilitating the delivery and feeding of the newborn
• Vasopressin: non-peptide which induces water reabsorption in the kidney (also called antidiuretic hormone)
• Somatostatin: a tetrapeptide that inhibits growth hormone release
• Insulin: Hormone composed of 51 AA synthesized in the pancreas. It stimulates the abortion of glucose by the cells. Its absence causes diabetes. Insulin was the first peptide to be sequenced by chemical methods. For this work, Frederick Sanger received the Nobel Prize in Chemistry in 1958. It consists of two polypeptide chains linked by three disulfide bridges.
• Glucagon: Hormone composed of 29 AA released by the pancreas when blood sugar levels are high. It causes glycogen in the liver to hydrolyze to generate glucose. Its effects are the opposite of those of insulin.

3. Neurotransmission: Neurotransmitters are chemical signals produced in a presynaptic nerve terminal, which through a specific receptor exert their action on the post-synaptic neuron. The peptide neurotransmitters are enkephalins (pentapeptides), endorphins (of 31 amino acids), and substance P.

4. Antibiotic: Valinomycin and gramicidin S are two cyclic peptides with an antibiotic action. Both contain D-series amino acids, as well as other non-protein amino acids. Valinomycin is an ionophore: it is able to transport potassium ions through the biological membranes.

5. Antioxidants: Glutathione is a tripeptide that acts as a cellular antioxidant. It reduces reactive oxygen species (such as H-peroxide) thanks to the enzyme glutathione peroxidase. Antioxidant classifications:

• Inhibitors of Neurotransmitters: Acting as a biological competitor, decreases the release of neurotransmitters. This leads to muscle relaxation and reduces facial wrinkles that are produced by muscle movement. In short, it reduces wrinkles due to expression.
• Signal Peptides: Those that will stimulate fibroblasts and in turn stimulate the production of collagen and elastin fibers, keratin, fibronectin, as well as boosting skin hydration by improving the production of hyaluronic acid.
• Transport Peptides: They improve the production and repair of collagen fibers by capturing metals such as copper and transporting them to metabolic processes in the enzymatic synthesis of these processes.

From a certain age (mainly from around the age of 30), the skin stops working so actively. Its regenerative activity starts to decrease, a decrease that accelerates when the body reaches 40 years old. Collagen and elastin deteriorate, and fibroblast activity diminishes. Therefore, the skin loses its firmness, and expression lines appear. It is the peptides that can help the skin to produce the substances it needs (such as collagen, which is fundamental for elasticity) to remain firm and look good. They help us fight very effectively against skin aging by correcting expression wrinkles that are difficult to conceal. Every time we laugh, cry, blink, etc., the skin is subjected to micro-tensions. As the years go by, the dermis becomes less elastic and more sensitive to the contractions and stretching to which it is exposed. Therefore, the well-known facial expression wrinkles are formed (crows feet at the corners of the eyes, frown lines, etc.), deepening as time goes by and leaving a mark that is increasingly deep and difficult to remedy.