Enzyme and heavy metals

Mercury Liver function and heavy metals If high levels of heavy metals are found then a common Naturopathic approach is the implementation of a liver detoxification program.

Enzyme and heavy metals

Enzyme inhibitors are molecules that interact in some way with the enzyme to prevent it from working in the normal manner. There are a variety of types of inhibitors including: Poisons and drugs are examples of enzyme inhibitors.

Enzyme Inhibitors

A nonspecific inhibition effects all enzymes in the same way. Non-specific methods of inhibition include any physical or chemical changes which ultimately denatures the protein portion of the enzyme and are therefore irreversible.

Usually, the reaction rate increases with temperature, but with enzyme reactions, a point is reached when the reaction rate decreases with increasing temperature. At high temperatures the protein part of the enzyme begins to denature, thus inhibiting the reaction.


What happens to the active site and the molecular geometry of the enzyme as it is denatured? Enzyme activity is also controlled by pH. As the pH is decreased or increased, the nature of the various acid and amine groups on side chains is altered with resulting changes in the overall shape structure of the enzyme.

Excess of either acid or base causes denaturing of protein. What type of bonds are disrupted by this action? Name some other denaturing methods to inhibit or destroy enzyme activity.

If an enzyme has been denatured, is it likely that its enzyme activity can be restored? Is the inhibition reversible or irreversible? Specific Inhibitors exert their effects upon a single enzyme. Most poisons work by specific inhibition of enzymes.

Many drugs also work by inhibiting enzymes in bacteria, viruses, or cancerous cells and will be discussed later. A competitive inhibitor is any compound which closely resembles the chemical structure and molecular geometry of the substrate.

The inhibitor competes for the same active site as the substrate molecule. The inhibitor may interact with the enzyme at the active site, but no reaction takes place. The inhibitor is "stuck" on the enzyme and prevents any substrate molecules from reacting with the enzyme. However, a competitive inhibition is usually reversible if sufficient substrate molecules are available to ultimately displace the inhibitor.

Therefore, the amount of enzyme inhibition depends upon the inhibitor concentration, substrate concentration, and the relative affinities of the inhibitor and substrate for the active site.

If the concentration of inhibitor is less than that of the substrate and the substrate has a higher affinity for the active site, is the enzyme inhibited a lot, or a little? If the concentration of inhibitor is more than that of the substrate is the enzyme inhibited a lot, or a little?

Ethanol is metabolized in the body by oxidation to acetaldehyde, which is in turn further oxidized to acetic acid by aldehyde oxidase enzymes. Normally, the second reaction is rapid so that acetaldehyde does not accumulate in the body. A drug, disulfiram Antabuse inhibits the aldehyde oxidase which causes the accumulation of acetaldehyde with subsequent unpleasant side-effects of nausea and vomiting.

This drug is sometimes used to help people overcome the drinking habit. Methanol poisoning occurs because methanol is oxidized to formaldehyde and formic acid which attack the optic nerve causing blindness.

Ethanol is given as an antidote for methanol poisoning because ethanol competitively inhibits the oxidation of methanol. Ethanol is oxidized in preference to methanol and consequently, the oxidation of methanol is slowed down so that the toxic by-products do not have a chance to accumulate.

Ethylene glycol, if ingested, can be poisonous. Ethylene glycol is oxidized by the same enzymes used in the previous examples by ethanol and methanol.

Describe how ethanol can be used as an antidote.

Enzyme and heavy metals

A noncompetitive inhibitor is a substance that interacts with the enyzme, but usually not at the active site. The noncompetitive inhibitor reacts either remote from or very close to the active site. The net effect of a non competitive inhibitor is to change the shape of the enzyme and thus the active site, so that the substrate can no longer interact with the enzyme to give a reaction.

Non competitive inhibitors are usually reversible, but are not influenced by concentrations of the substrate as is the case for a reversible competive inhibitor. See the graphic on the left.

Enzyme inhibitors

Irreversible Inhibitors form strong covalent bonds with an enzyme. These inhibitors may act at, near, or remote from the active site. Consequently, they may not be displaced by the addition of excess substrate.

In any case, the basic structure of the enzyme is modified to the degree that it ceases to work.Heavy metals such as Ag +, Hg 2+, Pb 2+ have strong affinities for -SH groups. Nerve gases such as diisopropylfluorophosphate (DFP) inhibit the active site of acetylcholine esterase by reacting with the hydroxyl group of serine to make an ester.

In addition to the enzyme products we manufacture and supply, we also provide cGMP certifiable laboratory services.

Enzyme and heavy metals

Enzyme identification, activity, and stability, as well as testing for heavy metals and microbial pathogens are among the lab services we provide to our customers. Heavy metal poisoning You are probably aware that compounds containing heavy metals such as lead, mercury, copper or silver are poisonous.

This is because ions of these metals are non-competitive inhibitors for several enzymes. Metals and vitamins can can act as co-factors and increase the metabolic efficiency of enzyme activity. But excess heavy metal exposure such as Mercury can be toxic to the enzyme, it then binds to the active site of each enzyme that is exposed and de activated it.

The sensitivity of urease to heavy metal ions is due to the presence of multiple cysteine residue, of which one, conserved principally to all known ureases, is located in the mobile flap of the active site of the enzyme (Todd and Hausinger, ). Heavy metals may inactivate enzyme reactions by complexing the substrate, by reacting with protein-active groups of enzymes, or by reacting with the enzyme-substrate complex (Deng and Tabatabai, ) or indirectly by altering the microbial community which synthesises enzymes (Kandeler et al., ).

enzyme inhibitors