Biosynthesis of food constituents: Peptides - a review

Abstract

Peptides display a wide variety of biological functions and many of them have remarkable physiological properties. Some are widely distributed in nature and found in many different organisms, whereas others are only of a restricted occurrence. For example, peptides function as neurotransmitters and hormones and thus control many physiological processes. Furthermore, the toxic principles of some plants and mushrooms, insect, snake, and spider venoms are usually peptides.Peptides are biosynthesised by ribosomal and nonribosomal (multi-functional enzyme) processes from a wide range of amino acids. Ribosomal peptide biosynthesis leads to enzymes, peptide hormones, and many other physiologically active peptides. Nonribosomal peptide biosynthesis is responsible for the formation of glutathione, histidine-containing dipeptides of skeletal muscles, peptide toxins, and peptide antibiotics. The mechanisms of these processes are, however, beyond the scope of this review.Many structures biosynthesised by ribosomal processes are additionally modified. Glycopeptides are produced by adding sugar residues via O-glycoside linkages to the hydroxyls of serine and threonine residues or via N-glycoside linkages to the amino group of asparagine. Phosphopeptides and phosphoproteins have the hydroxyl group of serine or threonine esterified with phosphoric acid. Many peptides contain a pyroglutamic (glutiminic) acid residue at the N-terminus, which is a consequence of glutamic acid intramolecular cyclisation between the γ-carboxyl and the α-amino group. The C-terminal carboxylic acids may also frequently be converted to an amide.Nonribosomal processes synthesise many natural peptides occurring in foods. These peptides are formed by a sequence of enzyme-controlled reactions. During these processes, each amino acid (often not encoded by DNA) is added (after activation by conversion into AMP esters) as a result of the specificity of the enzyme involved. This review article gives a brief survey of principal pathways that lead to the biosynthesis of most important peptides occurring in foods. Glutathione, selected plant γ-glutamyl peptides, and animal histidine dipeptides are included in this review. Biosynthesis of Food

Changes of S-alk(en)ylcysteine sulfoxide levels during the growth of different garlic morphotypes

“…At this stage, total concentrations of all three cysteine sulfoxides in the leaves (Figure 2) and pseudostems ( Figure 3) were typically 2-4 times higher compared to those present in the bulbs (Figure 4) and roots ( Figure 5). These findings support the general assumption that the green parts of garlic are the most important sites of cysteine sulfoxide biosynthesis, although some biogenesis may also occur in the bulbs (Lancaster & Shaw 1989;Lawson 1996;Hughes et al 2005;Velíšek & Cejpek 2009). A dramatic decline in the cysteine sulfoxide contents was observed both in the leaves and pseudostems at the beginning of April (between samples No.…”

Medicinal and therapeutic properties of garlic, garlic essential oil, and garlic-based snack food: An updated review

“…Garlic which has medicinally chemicals compounds primarily γ-l-glutamyl-l-cysteine, is found in mature garlic bulbs ( 115 ). The amino acid alliin, which is an alkyl derivative of cysteine alkyl sulfoxide, is the major component in whole garlic bulbs.…”

Profiles of S-alk(en)ylcysteine sulfoxides in various garlic genotypes

“…These amino acids are enzymatically formed by hydrolysis of the corresponding γ-glutamyl-Salk(en)ylcysteine storage dipeptides (Lancaster & Shaw 1989;Velíšek & Cejpek 2009). In the intact tissue, S-alk(en)ylcysteine sulfoxides are located in the cytoplasm.…”