Toxic Chemicals and its Effect on Enzeme

Toxic Chemicals

There are number of chemicals in the environment. Some of these are toxic and rest are non-toxic. The toxic chemicals are discharged by industries into air, water and soil. They get into human food chain from the environment. Once they enter our biological system, they disturb our biological processes leading in some caases to fatal diseases. Chemical toxicology is a branch of the modern technology for study of toxic chemicals and mode of action.

Schwardz used the term “concentration window” to draw the arbitrary lines of demarcation.

a) Essential at trace level for substance of trace level.
b) Deficient at lower than (a) causing metabolic disorder.
c) Toxic at higher than (a) causing adverse effect.






The effects of Toxic Chemicals on Enzyme

In general toxic chemicals attack the active sites of enzymes inhibiting essential enzyme function. Heavy metal atom e.g., Hg2+, Pb2+, Cd2+ act as a effective enzyme inhibitors. They have affinity for sulphur containing ligands e.g., SCH3 and –SH in methionic and cystonic amino acid which are the part of enzyme structure.


SH(Enzyme)SH + Hg2+ >>> S (Enzyme)SHg + 2H+


Metalloenzymes contain metals in their structures. Their action is inhibited when one metal ion of metallo-enzymes is replaced by another metal ion of similar size and charge.

As for example, Zn2+ in some metallo-enzymes is substituted by Cd+2 which leads to cadmium toxiacity. The enzyme inhibited by Cd2+ include alcohol dehydrogenase amylase, peptidase.