Protein content = nitrogen content of protein sample *6.25

Protein can be hydrolyzed by acids, alkalis, and proteases to release more than 20 amino acids.

Configuration and optical activity

All are α-amino acids (except Pro). All are L-α-amino acids. All are optically active (except Gly). Different α-amino acids have different R side chains.

The pH of a solution at which the net charge of an amino acid is zero *pH<pI, positive charge *pH=pI, no charge *pH>pI, negative charge

Commonly used methods to separate mixed amino acids: Certain amino acids can be precipitated from the mixture by utilizing the minimum solubility at the isoelectric point. Separation is carried out by utilizing the difference in charge of different amino acids at the same pH.

Neutral amino acids: pI=(pK-COOH pK-NH3)/2

Acidic amino acids: pI=(pK1-COOH pK2-COOH)/2

Basic amino acids: pI=(pK2-NH3 pK3-NH3)/2

The law of isoelectric point

The pK value of the zwitterion before and after dissociation

Basic elements: C, H, O, N, S

Trace elements: P, I, Se... Fe, Mn, Mg, Cu, Zn, Co...

non-polar

polarity

1. Color status: Amino acids are usually colorless crystals, their color is unknown It appears as pure colorless or white crystalline form. Different amino acids may form different crystalline shapes due to their specific structures, and these shapes can be used to identify different amino acid types.

2. Solubility: Most amino acids are soluble in water, especially in warm water. Except for cystine and tyrosine, the rest of the amino acids are also better soluble in cold water. For organic solvents, amino acids are generally insoluble or slightly soluble in ethanol, ether, etc., with the exception of proline and hydroxylamine (not one of the 20 standard amino acids), which are soluble in ethanol and ether.

3.Taste: Amino acids have a variety of different flavors, including sour, sweet, bitter and umami. For example, glutamic acid (monosodium glutamate, the main component of MSG) has a distinct umami taste, glycine is sweet, and some amino acids may be bitter or tasteless.

concepts, features

concept

calculate

Ninhydrin reaction

Amino acids containing conjugated double bonds (tyrosine, phenylalanine, and tryptophan) have UV-absorbing properties

Only aromatic amino acids have UV absorption capabilities (because they contain the R side chain of a benzene ring conjugated double bond). Tyrosine λmax: 275nm Phenylalanine λmax: 259nm Tryptophan λmax: 279nm

* Found in collagen *Pro Hydroxylation requires Vitamin C

subtopic

*Exists in coagulation factors *Glu modification requires vitamin K

Cys is formed through disulfide bonds