What is Synthesis of Specialized Products from Amino Acids
In addition to serving as building blocks for proteins, amino acids are precursors of many nitrogen containing compounds that have important biological functions. These are:
a) Synthesis of porphyrins - Porphyrins is the cyclic compounds that readily bind metal ions, usually Fe2+ or Fe3+. The most common metalloporphyrin in humans is heme, which is the prosthetic group for the following compounds:
Haemoglobin - You may already know that haemoglobin is present in the red blood cells (RBC) and transports oxygen from lungs to tissues.
Myoglobin - It is present in muscles and stores oxygen as a reserve against oxygen deprivation.
Cytochromes - They take part in oxidation-reduction reactions since they contain iron which can accept electrons to exist in the ferrous (Fe2+) state or give up electrons to exist in ferric (Fe3+) state. Thus several cytochromes b, c1, c2' a and a3 are present in the mitochondria1 respiratory chain acting as carriers of electrons.
Catalase - It is an enzyme found in blood, bone marrow, mucous membrane, kidney and liver. The function is to destroy the highly toxic hydrogen peroxide (H202) formed during various oxidation reactions in the body to the non-toxic water (H20)
2 H202 →b 2H20 + 02
Tryptophanpyrrolase - It is an enzyme which catalyses the first step in the degradation of tryptophan, which is oxidative reaction requiring oxygen. Hence, this enzyme is also called tryptophan oxygenase.
b) Synthesis of creatine - Creatine phosphate, the phosphorylated derivative of creatine is found in muscles. It is a high energy compound that can reversibly donate a phosphate group to ADP to form ATP. It is synthesized from glycine.
c) Synthesis of histamine- Histamine is a powerful vasodilator (causing relaxation of the smooth muscle of the vascular system) and is formed by the decarboxylation of the amino acid histidine. It is secreted by must cells (present in the connective tissue) as a result of allergic reactions or trauma. It is a chemical messenger that mediates a wide range of cellular responses.
d) Synthesis of serotonin - It is also called 5-hydroxytryptamine and is synthesized from tryptophan (the aromatic amino acid) and involves decarboxylation reaction. Serotonin functions as a neurotransmitter.
e) Synthesis of catecholamines - Dopamine, norepinephrine (noradrenalin) and .epinephrine (adrenalin) are biologically active amines (containing amino groups) that are collectively termed as catecholamines. They are classified as hormones.
Dopamine and norepinephrine function as neurotransmitters in the brain and the autonomic nervous system. Norepinephrine and epinephrine are synthesized in the adrenal medulta (the inner, reddish-brown portion of the adrenal glands that synthesizes, stores, and releases epinephrine and norepinephrine). The catecholamines are synthesized from tyrosine (tyrosine + dopaininej norepinephrine + epinephrine).