Radioactive Isotopes in biogenetic studies (Part - 2) I Pharmacognosy and Phytochemistry (T. T. B. Pharm sem-V) UNIT - I

 

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.

Steps in Tracer Technique

1.                  Selection of Radioisotopes

2.                  Preparation of Radioisotopes.

3.      Introduction/Insertion of Radiolabelled compound in biological system (Plant part).

4.        Seperation and determination of labelled compound in various biochemical reaction

1.      Selection of Radioisotopes

1.          Selection based on according to half life

¹⁰C₆  half life few second

¹¹C₆  half life few minute

¹⁴C₆   half life around six thousand years (Mainly used)

³H₁   (Tritium) half life 12 years

2.                  2. Preparation of labelled compound:

            (a)    Growing chlorella in atmosphere of    ¹⁴CO₂ 

             (b)   Nuclear Reactor/Acceralator

                 ¹⁴N₇, + ¹⁴n0            ¹⁴C₆, +    ¹P₆ 

(c)Tritium gas: Tritium labelled compound  (³H₁) are commercially available. Tritium labelling is effected by catallytic exchange in aqueous media by hydrogenation of unsaturated compd with tritium gas.

(d) by the use of Organic Synthesis:

   CH3MgBr   + ¹⁴CO₂            CH3¹⁴COOHMgBr +  H2O

                                                                      CH3¹⁴COOH  + MgOHBr

                     Radio labelled

                 Acetic acid

                      

3.                  3.  Insertion of Radiolabelled compound in plant part:

Precaution

The precursor should react at necessary site of synthesis in plants.

 Plant at the experiment time should synthesize the compound under investigation.

 The dose given is for short period.

1.                  Root feeding: When the root is biosynthetic site (Ex- Tobacco and Datura alkaloid).

2.                  Stem Feeding: Cut end of stem immersed in water, nutrient and radiolabelled compound.

3.                  Direct Injection: Which have hollow stem (Umbelliferous fruits).

4.                  Infilteration: Plant rooted in soil and other support method it is also called Wick Feeding method.

5.                  Floating method: Substrate solution which contain Radioactive compound.

6.                  Spray technique.

 4. Separation or Isolation of Radiolabelled compound and 

detection of radioisotope labelled compound :

Depends on Nature of drugs and Sources of drugs.

Soft tissue- Infusion, Maceration

Hard Tissue- Decoction, hot percolation

Unorganised drugs- Maceration

Alkaloid, Glycoside, Flavonoids- Slightly polar solvent.

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