8/6/2019 Enzyme Cofactors and Inhibitors

1/20

` Non-protein substances essential for enzymes tofunction effectively.

` When an enzyme is linked to a cofactor, the

complex is called a holoenzyme.` When an enzyme is not linked to a cofactor, the

complex is called an apoenzyme.

8/6/2019 Enzyme Cofactors and Inhibitors

2/20

T here are three types:1. Activators these are believed to help mould

either the enzyme or the substrate so that the

enzyme/substrate complex can be formed. Eg.Ca 2+ ions are needed so that thrombokinase canconvert prothrombin to thrombin. Cl - ions areneeded for salivary amylase to convert starch to

maltose.

8/6/2019 Enzyme Cofactors and Inhibitors

3/20

2. Coenzymes these are non protein organicmolecules not bound to the enzyme. T heytransfer chemical groups, atoms or electrons

from one enzyme to another. Many are vitaminsor their derivatives. Eg. NAD (Nicotamide Adenine Dinucleotide a derivative of nicotinicacid B vitamin) is a hydrogen acceptor and a

coenzyme to dehydrogenases.

8/6/2019 Enzyme Cofactors and Inhibitors

4/20

3 . Prosthetic groups these are organic moleculesbound to the enzyme. Eg. Haem (a flat ringmolecule containing iron). It is a prosthetic group

of the electron carrier cytochrome oxidase andcatalase.

8/6/2019 Enzyme Cofactors and Inhibitors

5/20

` T hese prevent the action of enzymes or reducetheir catalytic power.

` T here are two main types:

- Reversible inhibitors- Irreversible inhibitors.

8/6/2019 Enzyme Cofactors and Inhibitors

6/20

T hese do not cause any permament damage tothe enzymes. T herefore, after the inhibitor isremoved, the enzyme can function normally

again.T

here are two types;

a. Competitiveb. Non-competitive

8/6/2019 Enzyme Cofactors and Inhibitors

7/20

` T hese have similar shape to the substrate andcompete with it to occupy the active site. If moresubstrate is added, the effect of the inhibitors is

reduced.

8/6/2019 Enzyme Cofactors and Inhibitors

8/20

8/6/2019 Enzyme Cofactors and Inhibitors

9/20

1. - T he antifreeze ethylene glycol is rapidlyconverted to oxalic acid if ingested.

- Oxalic acid causes irreversible damage tokidneys.

- T he active site of the enzyme (alcoholdehydrogenase) which converts ethylene glycolto oxalic acid will accept ethanol.

- If the person who ingested ethylene glycol isgiven large doses of ethanol, the ethanol acts asa competitive inhibitor allowing the ethyleneglycol to be excreted or removed.

8/6/2019 Enzyme Cofactors and Inhibitors

10/20

2. Penicillin occupies the active site of theenzymes that are essential for the synthesis of bacterial cell walls.

3 . Succinic dehydrogenase takes part in the Krebscycle converting succinic acid to fumaric acid.Malonate is similar in structure to succinic acid.Malonate ions occupy the active site of the

enzyme preventing further reaction.

8/6/2019 Enzyme Cofactors and Inhibitors

11/20

` T hese do not compete for the active site of theenzyme. Rather, they bind elsewhere on theenzyme or the cofactor, thus disrupting the shape

of the enzyme and hence the active site.

8/6/2019 Enzyme Cofactors and Inhibitors

12/20

8/6/2019 Enzyme Cofactors and Inhibitors

13/20

` T hey change the shape and structure of theenzyme so that it is permanently damaged. i.e. isinactivated permanently.

` T his type of inhibition occurs slowly but the effectsare devastating. It is never used in cells to controlmetabolism.

8/6/2019 Enzyme Cofactors and Inhibitors

14/20

1. Arsenic, cyanide and mercury. Nerve gases aredangerous because they inactivate the enzymeacetylcholinesterase. T his enzyme destroys the

neurotransmitter acetylcholine after it carriesimpulses across a synapse. When it is notbroken down, the muscle goes into prolongedspasms and breathing and swallowing becomes

impossible.

8/6/2019 Enzyme Cofactors and Inhibitors

15/20

` 2. Pyrethroids and nicotine (insecticides) directlyaffects the synapses of the CNS in insects. T heneurotransmitters are not broken down, there is

constant stimulation resulting in twitching,convulsions and death.

8/6/2019 Enzyme Cofactors and Inhibitors

16/20

` Regulatory enzymes are used in the control of themany metabolic reactions within a cell.

` T hey are also called allosteric enzymes.

(Allosteric another place)` Regulatory enzymes have another site to which

another molecule can bind and act as an inhibitor or activator.

` Allosteric control is different from non-competitiveinhibition because the molecule can inhibit or activate the enzyme.

8/6/2019 Enzyme Cofactors and Inhibitors

17/20

` Regulatory enzymes are found in metabolicpathways.

` T he enzymes are found near to or at the

beginning of the pathway and is inhibited or activated by an end product of the chain.

8/6/2019 Enzyme Cofactors and Inhibitors

18/20

T heir use in technology is very promisingbecause:

1. T hey can work at low temperature.

2. T hey can work at normal pressures.3 . T heir pH ranges can be very easily maintained.4. T hey can be produced using genetic

engineering.

8/6/2019 Enzyme Cofactors and Inhibitors

19/20

Rennin is used to clot milk when making cheese.Enzymes from yeast used in brewing and baking.Cellulases and pectinases used to clarify fruit

juices.T rypsin used to predigest baby foods.Proteases used to lower protein content of flour when making biscuits.

A variety of enzymes used to make syrups fromstarches.

8/6/2019 Enzyme Cofactors and Inhibitors

20/20

` U sed in detergents to digest dirt especiallyproteins, sweat etc.

` Enzymes are presently being developed that nip

off bobbles formed on cotton when washed.` U sed in rubber industry to produce oxygen and

convert latex to foam rubber.