**6. Amino acids**

Amino acids are nutrients that function as raw material for protein formation. According to their classification due to their requirement in the diet, they are classified as essential, nonessential, and semi-essential. Their most important function is the formation of peptides, structural proteins, enzymes, transporter proteins, immunoproteins, and hormones. However, each has special chemical functions in which they are exchanged or cede methyl or sulfhydroxyl groups in choline synthesis or substance detoxification. Some of these, such as glycine, cysteine, glutamic acid, or taurine, assume the role of antioxidants, and under extreme conditions when other energy sources are insufficient, these are utilized to produce energy through glyconeogenesis; each amino acid possesses different specific and concrete functions (Morales-González, 2009).

#### **6.1 Glycine (Gli)**

This is the simplest amino acid of all, and it is one of the so-called non-essential amino acids; thus, no minimal nutritional contribution is required, given that there are substances available in the organism for its synthesis. Glycine (C2H5NO2) is produced in hepatocyte mitochondria from 3-D-phosphoglycerate, giving rise to serine, and in the presence of pyridoxal phosphate, serine hydroxymethyltransferase removes one carbon atom, thus producing glycine. It can also be constituted from carbon dioxide, ammonium, and from N5N10-methylenoTetrahydrofolate (TFH) in the same manner as in the mitochondria (Morales-González, 2009; Mathews-Van Holde, 1998).

Glycine is found at high concentrations in the organism, functioning as an important carbon donor for the formation of numerous essential compounds. It also functions in the biosynthesis of multiple compounds, such as the heme group, purines, proteins, nucleotides, nucleic acids, creatinine, conjugated bile salts, and porphyrins, or it can be degraded and converted into serine. In the brain, it functions as a neurotransmitter inhibitor; in addition, it serves as an extracellular communications molecule; therefore, it possesses different antioxidant protector effects (Morales-González, 2009).

#### **6.1.1 Antioxidant activity**

Glycine possess a protector effect due to that it prevents due to that it prevents the decrease of antioxidant hepatic enzyme activity after hemorrhagic processes; this effect can be due to that glycine blocks the activation of Kupffer cells, which produce FR. Likewise, glycine exercises an ascorbate oxidation protector effect by means of cupric ions; consequently, it diminishes hydroxyl radical generation. In addition to this, glycine forms part of glutathione, tripeptidic and intracellular, that combats FR and maintains some essential biological molecules in a reduced chemical state (Morales-González, 2009).

A group of researchers demonstrated the hepatoprotector effect of glycine and vitamin E in a study conducted in rats in which Partial hepatoctomy (PH) was practiced with subsequent administration of these antioxidants; finally, it was observed that treatment with either of the two antioxidants causes an increase in the peroxidase dismutase enzyme; it diminishes Thiobarbituric acid (TBARS) levels, exhibiting the protector effect in hepatic regeneration (Parra-Vizuet et al., 2009).
