1. Different ingredients
Amino acids are the basic substances that constitute the protein required for animal nutrition. It is an organic compound containing basic amino groups and acidic carboxyl groups. The amino group attached to the α-carbon is an α-amino acid. Most of the amino acids that make up proteins are α-amino acids.
Free amino acids are organic compounds containing both amino groups (-NH2) and carboxyl groups (-COOH). Amino acids also contain cyclic compounds (imino acids) in which the hydrogen of an amino group is substituted with other parts of the molecule to form an imine.
2. Different characteristics
The free amino acid has an amino group on the α-carbon atom adjacent to the carboxyl group, so it is called α-amino acid. Natural protein is a complex polymer compound composed of different α-amino acids through peptide bonds, and its structure and composition are very complicated.
Most amino acids are soluble in water. The solubility of different amino acids in water is different, such as lysine, arginine, proline solubility is greater, tyrosine, cysteine, histidine solubility is very small. Various amino acids can be dissolved in strong alkali and strong acid. But amino acids are insoluble or slightly soluble in ethanol.
3. Different synthesis principles
The amino and carboxyl groups are combined on the same carbon atom and are called α-amino acids. Most of the naturally-derived amino acids are α-amino acids (R-CHNH2-COOH), and the compounds where the α-amino acids lose water to form a peptide bond are proteins or peptides. Because amino groups move from α to adjacent carbon atoms in sequence, they are called β-, γ-, δ-amino acids, etc., but they do not exist in proteins.