Heavy metal poisoning is an example of

noncompetitive inhibitor of an enzyme. What type of bonds are affected

by heavy metal ions?

Covalent bonds make a permanent change to enzyme’s active site shape.e.g. organophosphate insecticides & nerve gases.Enzyme is permanently inhibited.

Irreversible Inhibition

Sarin nerve gas

Foreign vs.Normal Inhibition

• Foreign: reversible & irreversible– Caused by the influence of agents foreign

to the normal cells

• Normal: allosteric enzymes– Regulation by “normal” cell components

Allosteric regulation of Enzyme Activity Allosteric enzymes have 2 or more protein chains

(o4 structure)And 2 kinds of binding sites:

1.Substrate binding site = active site2.Regulator binding site - molecule binding here alters structure of active site

Reversible and

rapid in action

Regulators bind to a specific site on the enzyme called the allosteric site

positive regulatornegative regulator

Feedback control is a common mechanism for allosteric activity

enzyme 1 enzyme 2 enzyme 3

A ----> B ----> C ----> D Product D is a negative regulator of enzyme 1, so...

Feedback & Feedforward control:Activation or inhibition of the 1st reaction in a reaction sequence is controlled bya product of the reaction sequence.

Feedback animation

If A is accumulating, speed up down stream products to use “A” up.

In positive feedforward, earlier reactants in a metabolic reaction sequence

feed-forward positively on later steps

The enzyme phosphofructokinase (PFK) is regulated by:

• High concentrations of ATP, which inhibit PFK • High concentrations of ADP, which stimulate PFK • High concentrations of AMP, which stimulate PFK • High concentrations of citrate, which inhibit PFK ATP and citrate are allosteric negative regulators ADP and AMP are allosteric positive regulators.

DNA Digestion lab animation

Restriction Fragment Lengths Polymorphism

Early genetic splicing experiment

Polymerase Chain Reaction

Another mechanism of regulating enzyme activity is to keep dangerous enzymes in compartments where

access to their substrates is limited. e.g. proteolysis of cell proteins by enzymes is controlled by keeping these enzymes within lysosomes

Or, take a proteolytic enzyme (dangerous because they break peptide bonds)

and keep it in an inactive form until needed.

The inactive form of a proteolytic enzyme is called a proenzyme or

a zymogen

Digestive and blood clotting enzymes are kept this way until needed,

then they are activated!

Covalent modification: enzyme activity controlled byother enzymes or chemicals

Enzyme exists in 2 states: modified (e.g. phosphorylated) = “activated” unmodified (e.g. unphosphorylated) = “inactivated”

Here the proteolytic enzyme zymogen form is activated by HCl acid in the stomach:

e.g. pepsinogen is converted to pepsin when needed.

Conversion of zymogen to proteolytic enzyme often involves removal of a polypeptide chain segment from the zymogen

structure.

Bacterial infection (pathogens) account for many severe diseases world-wide.Examples:Tuberculosis and LeprosyStaph and StrepSyphilisBubonic plagueCholera and typhoid feverGastroenteritisUrinary tract and Wound infectionsMany sexually transmitted diseases

Much research on fighting bacterial infections revolves around inactivating bacterial enzymes.

Earliest “antibiotics” were the SulfaSulfa drugs

Antibiotics kill or stop the growth of bacteria.

Sulfanilamide is a structural mimic of PABA (p-aminobenzoic acid) which is

needed by bacteria to make a coenzyme called Folic acid.

Humans get Folic acid from diet, don’t use PABA.

Structures of selected antibiotic sulfa drugs in use today

PABA

PenicillinsDiscovered accidentally by Fleming in 1928Developed ten years later into penicillin productsInhibit enzyme: transpeptidase used to strengthen polysaccharide strands in gram + bacterial cell walls.

Structures of selected penicillins in use today

The selective binding of penicillin to

the active site of transpeptidase.

Disorders and diseases frequently “leak” organ enzymes into blood and urine.

Doctors utilize this for diagnoses of various ailments.