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

Glutathione
(G-SH or G-S-S-G) γ-L-glutamyl-L-cysteinylglycine (γ-amide bond)

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
Occurrence Function
 * carnosine [[File:karnosine.jpg]], anserin [[File:anserin.jpg]], balenin [[File:balenin.jpg]]
 * in meat
 * 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]]

Related Articles

 * Amino acids
 * Proteins
 * Amino acids, peptides, proteins