It is a tripeptide secreted by hypothalamus.   —OOc—Glu—His—Pro—NH2 Functions: It stimulates pituitary gland to release thyrotropic hormone.

The reversible oxidation–reduction of glutathione is important for many of its biological functions. It maintains a ratio of about 10011 of GSH to G—S—S—G. Glutathione (reduced) performs specialised functions in erythrocytes. It maintains RBC membrane structure in integrity. It protects haemoglobin from getting oxidised by agents such as H2O2. It involves in the transport of…

It is a tripeptide composed of three amino acids. Chemically, glutathione is γ—glutamyl—cysteine—glycine. It is widely distributed in nature and exists in reduced or oxidised states. Structure of glutathione is as given below:

Several peptides occur in the living organisms that display a wide spectrum of biological functions.

The dimensions of a fully extended polypeptide chain are shown in Figure 3.2. The two adjacent α-carbon atoms are placed at a distance of 0.36 nm.   α-carbon—N(NH3) = 0.147 nmα-carbon—C(COO) = 0.153 nmC—O = 0.123 nm(Peptide bond)   C—N = 0.132 nmN—H = 0.1 nm Figure 3.2 Dimension of a Fully Extended Polypeptide Chain

  One-letter symbol E—C—G   Three-letter symbol Glu — Cys — Gly   Peptide name Glutamyl — Cystine — Glycine

For naming an amino acid, suffixes –ine (glycine), –an (tryptophan), and –ate (glutamate) are changed to -yl with the exception of C-terminal amino acid. Example: H3N — Glutamate — Cystine — Glycine COO−

The amino acids in a peptide bond are represented by a three-letter or one-letter abbreviation. This is the chemical shorthand way to write proteins.

The peptide chains are written with the free amino end (N-terminal residue) at the left and the free carboxyl end (C-terminal residue) at the right. The amino acid sequence is read from N-terminal end to C-terminal end. The protein biosynthesis also starts from the N-terminal amino acid.

The peptide bond is a rigid planar with partial double bond in character. It exists in transconfiguration. Both —C=O and —NH groups of peptide bonds are polar and are involved in hydrogen bond formation.