Utilization of Radioactive Isotopes in Biogenetic Studies ( Part – I ) I Pharmacognosy and Phytochemistry (T. Y. B. Pharm Sem –V) Unit -I

 

Introduction

1.      Living plants considered as biosynthetic laboratory primary as well as secondary metabolite.

2.      Different biosynthetic pathway

    Shikimic acid pathway     :      Aromatic amino acids

    Mevalonic acid pathway   :      Terpenes

    Acetate pathway          :      Fatty acids

   Amino acid pathway        :      Amino acid

Definitions:

Biosynthesis: Formation of a chemical compound by a living organisms

Biogenesis: Production or generation of living organisms from other living organisms.

Primary metabolites: Required for growth & normal physiological activity.

e.g. carbohydrates, fatty acids, amino acids, nucleic acids, proteins.

Secondary metabolites: Biosynthetically derived from primary metabolites. They represent chemical adaptations to environmental stresses, or act as defensive or protective against microorganisms, insect & higher herbivores.

e.g. Alkaloids, glycosides, resins, tannins

Isotopes

Iso  means  Same (Equal), Topes means Place

They occupy same place in periodic table. "Elements  with same atomic number but different atomic weight.

(Same number of protons but differ in neutrons).

Example-

               ¹²C₆               ¹³C₆               ¹⁴C₆  (Isotopes)

Atomic mass    =  No. of Protons + No. of Neutrons

Atomic Number =  No. of protons

Hydrogen Isotopes:

               ¹H₁                            ²H₁              ³H₁ 

          [1P]                [1P, IN]        [1P, 2 N]

        Hydrogen            Deuterium       Tritium

 

Two types of Isotopes

1.      Radioactive Isotopes (Radioisotopes)

2.      Stable Isotopes

 

1.      Radioactive Isotopes (Radioisotopes)

    Radio (Radiation) + Isotopes            Unstable Isotopes

The isotopes which emits the radiation are called Radioisotopes.

Decay with the emission of radiation (alpha, β, gama  radiation).

Example ³H,¹⁴C,³⁵S,¹³¹I, ²⁴Na, ⁴²K , ³⁵S , ³⁵S, ³⁵P, ¹³¹I

For biological investigation- Carbon and Hydrogen

For Metabolic studies- S, P & alkali & alkaline earth metals are used.

For studies on proteins, alkaloids & amino acids-labelled nitrogen atom give more specific information.

³H compound is commercially available.

 

2. Stable Isotopes:

 Stable isotopes are non-radioactive forms of atoms (they do not emit radiations).

Although they do not emit radiations, their unique properties enable them to be used in a

broad variety of applications, including water and soil management, environmental studies,

nutrition assessment studies and forensics.

 

 

Examples-     ²H, ¹³C, ¹⁵N, ¹⁸O

 

Used for labelled compounds as possible intermediates in biosynthetic pathways Usual

method of detection are: MASS Spectroscopy [¹⁵N, ¹⁸O]

   NMR Spectroscopy [²H, ¹³C]

 

 

Radio labelled Tracers (Radio labelled compound)

When one or more atom of chemical compound replaced by radioisotopes used- for the study of the biosynthetic pathway, is known as Radiotracers.

Radiotracer Technique:

The technique which utilises radioactive labelled compound to find out or to trace various precursors and intermediates involved at different stages of biosynthetic pathway at given rate and time.

 

In this technique, different isotope, mainly the radioactive isotopes which are incorporated into the presumed precursor of plant metabolites & used as marker in the biogenic studies. 

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