Enzymes (enzymes) are a unique type of protein that possess high catalytic activity and specificity. The synthesis and degradation of proteins, fats, sugars, and many complex chemical reactions in life processes are all closely related to enzymes. Approximately 700 types of enzymes have been discovered, which can be classified into six categories based on their functions: transferases, hydrolases, oxidoreductases, lyases, isomerases, ligases, or synthetases. Some enzymes in the body have different structures and sizes but share the same catalytic function, and these enzymes are called isozymes. For example, isocitrate dehydrogenase, malate dehydrogenase, and RNAase all belong to isozymes. Non-protein organic molecules or metals that bind to the enzyme structure are collectively referred to as co-enzymes. Some enzymes have been used in clinical treatments, such as amylase and pepsin which can aid digestion, streptokinase which can dissolve blood clots and abscesses, and ficin protease which can kill parasites and anti-inflammatory drugs.
The properties and identification reactions of enzymes are the same as those of proteins.
Peptides are the intermediate products of protein hydrolysis. Generally, they refer to substances composed of 2 to 20 amino acids, with a linear or cyclic structure. There is no clear boundary between polypeptides and proteins. Many polypeptides have biological activity. For example, leech peptides can coagulate blood, frog skin peptides can dilate blood vessels, and sea hare inhibitory substances can fight tumors. Some plant polypeptides are cyclic peptides with -S- chains, such as toxic cyclic peptides. Some peptides with phenolic compounds can lower blood pressure. There are also oxytocin peptides in the stems of the white flower licorice and anti-lipid breakdown peptides in ginseng.
The main difference between protein molecules and polypeptides lies in the more complex spatial layout of proteins. Polypeptides are α-amino acid compounds connected by peptide bonds and are also intermediate products of protein hydrolysis. Compounds formed by the dehydration contraction of two amino acid molecules are called dipeptides, and similarly, there are also tripeptides, tetrapeptides, pentapeptides, etc. Compounds formed by the dehydration condensation of three or more amino acid molecules can be called polypeptides. Polypeptides have a clear definition based on advanced organic chemistry. Proteins are an important component of all cells and tissues in the human body. Proteins must participate in all important components of the body. Generally speaking, proteins account for approximately 18% of all body qualities, and the most important thing is that they are related to life phenomena. Proteins are formed by polypeptide chains of amino acids "dehydrating and contracting" through coiling and folding, and have a certain spatial layout. In addition, protein is a highly non-specific macromolecule that is not easily absorbed and needs to be decomposed into amino acids or small peptides during digestion before it can be absorbed. When small peptides are absorbed intact into the circulation, there are no waste products or metabolites, and can be fully utilized by the body.
The protein content is high, usually above 10,000. The larger the molecular weight, the more surface antigenic determinants there are, the more stable the chemical structure, and it is less likely to be destroyed or eliminated by the body. They remain in the body for a long time, giving sufficient opportunity to come into contact with cells that produce antibodies and stimulating the body's immune response. Small molecule peptides have low antigenicity or no antigenicity at all.
Post time: 2025-08-21