Peptides can be classified into distinct categories based on their production processes. One such category is ribosomal peptides, which are synthesized through the translation of mRNA. Ribosomal peptides often function as hormones and signaling molecules within organisms. Examples include tachykinin peptides, vasoactive intestinal peptides, opioid peptides, pancreatic peptides, and calcitonin peptides. Organisms also produce ribosomal peptide antibiotics like microcins. To achieve their mature form, ribosomal peptides often undergo proteolysis, which involves the breakdown of proteins into smaller peptides or amino acids.
In contrast, nonribosomal peptides are synthesized by peptide-specific enzymes rather than by the ribosome. Nonribosomal peptides are frequently cyclic in nature, although linear nonribosomal peptides can also exist. These peptides can have highly intricate cyclic structures and are commonly found in plants, fungi, and single-celled organisms. Glutathione, a crucial component of antioxidant defenses in aerobic organisms, represents a prominent example of a nonribosomal peptide.
Milk peptides are derived from milk proteins and can be generated through enzymatic breakdown by digestive enzymes or by the proteinases produced by lactobacilli during milk fermentation. Additionally, peptones are peptides obtained from animal milk or meat that have undergone proteolytic digestion. Peptones are often employed as nutrient sources in laboratory settings for the cultivation of fungi and bacteria.
Furthermore, peptide fragments are typically generated as a result of enzymatic degradation performed in controlled laboratory conditions. However, natural degradation processes can also lead to the formation of peptide fragments.