Peptides (1. LF UK, NT)

Structure

• condensation (amino acids -› peptides)

• binding of some amino acids in an unusual way (Glu distal group COOH = γ-peptide bond)
• bound D-amino acids
• unusual amino acids bound
  • ß-alanine (3-aminopropionic) File:Beta-alanine.jpg, α-aminobutyric (2-aminobutyric) File:Alpha-aminobutyric.jpg, γ-aminobutyric (4-aminobutyric) File:Gamma-aminobutyric.jpg, taurine File:Taurine.jpg, 2-aminoacrylic (dehydroalanine ) File:2-aminoacrylic.jpg, (E)-2-aminocroton (dehydrobutyrin) File:Dehydrobutyrin.jpg, pyroglutam File:Pyroglutam.jpg

Classification

Number of bound monomers (amino acids)

• oligopeptides (2–10 amino acids)
• polypeptides (formerly macropeptides, 11–100 amino acids)

String type

• linear
• cyclical

type of bonds

• homodet (peptide bonds only)
• heterodet (peptide and other bonds)
  • disulfide -S-S-, ester (depsipeptides) -CO-O-R

Bound folders

• homeomeric containing only amino acids
• heteromeric (peptoids) containing also other compounds
  • nucleopeptides – phosphopeptides
  • lipopeptides – chromopeptides
  • glycopeptides – metallopeptides

Occurrence

• products of metabolism, natural peptides
• products of proteolysis, enzymatic or non-enzymatic hydrolysis
• synthetic peptides, substitute sweeteners

Properties

• biological activity
• sensory properties
• products of metabolism of lactic acid bacteria = bacteriocins
• nisin (Streptococcus cremoris, syn. Lactococcus lactis ssp. Lactis)
• preservative, stabilization of fermented products

Significant Peptides

Glutathione

(G-SH or G-S-S-G) γ-L-glutamyl-L-cysteinylglycine (γ-amide bond) File:Glutathione.jpg

Occurrence

• microorganisms, plants, animals
  • wheat flour (10-15 mg/kg)
  • meat (300-1500 mg/kg)

Function

• detoxification of toxic forms of oxygenu
• transport (transfer) of amino acids into cells
• metabolic processes (leukotriene biosynthesis)
• stabilization of the oxidation state of SH-proteins (substrate of peroxidase, glutathione reductase)
• technology

Chorleywood method of white bread production, ascorbic acid

• H₂A + ½ O₂ → A + H₂O (ascorbase)
• A + 2 G-SH → H₂A + G-S-S-G (glutathione dehydrogenase)
• G-S-S-G – without affecting the rheological properties of the dough
• G-SH – negative effect (gluten protein depolymerization)
• P-S-S-P + G-SH → P-S-S-G + P-SH

β-alanylhistidine dipeptides

• carnosine File:Karnosine.jpg, anserin File:Anserin.jpg, balenin File:Balenin.jpg

Occurrence

• in meat

Function

• participation in contraction of skeletal muscle
• buffering capacity of the muscle
• organoleptic properties

Products of proteolysis

• spontaneous proteolysis (autolysis)
  • desired maturation of meat (consistency, aroma), production of yeast autolysates (additives)
  • undesirable
• intentional proteolysis
  • cheese production (desired consistency, aroma)
  • production of malt (stabilization of beer foam)
  • production of protein hydrolysates
    • Enzymatic:
      • soy sauce
      • hydrolysates of waste proteins (blood, whey, caseins)
    • sour: soup spices and other preparations

Bitter peptides of enzyme hydrolysates and foods

• hydrophobic amino acids: Val, Leu, Ile, Phe, Tyr, Trp (M < 6000 Da)

Synthetic Peptides

• substitute sweetener Aspartame (Asp-Phe) File:Aspartame.jpg

Links

Related Articles

• Amino acids
• Proteins
• Amino acids, peptides, proteins

Source

• Incomplete citation of web. . [cit. 2012-03-10]. <https://el.lf1.cuni.cz/p51525121/>.