enzymes_catalysis

• EQUILIBRIA: THE FINAL RESTING POSITIONS OF THE REACTANT AND PRODUCTS.
• THIS IS AN IMPORTANT CONCEPT BECAUSE THIS IS WHERE THE REACTION COMPONENTS WILL BE WHEN THE REACTION IS COMPLETED.
• SPEED HAS NOTHING TO DO WITH EQUILIBRIUM.

• KINETICS: THE RATE AT WHICH AN EQUATION GOES TO COMPLETION.
• MODIFYING THE KINETICS OF A REACTION, SAY, TO MAKE IT GO FASTER, WILL NOT CHANGE THE EQUILIBRIUM OF THE EQUATION.

EQUILIBRIUM FREE ENERGY CHANGES ARE INDICATED BY DELTA G

ACTIVATION FREE ENERGY CHANGES ARE INDICATED BY DELTA G DOUBLE DAGGER

CHANGES TO DELTA G DOUBLE DAGGER DO NOT AFFECT DELTA G

GENERALLY, ENZYMES ENHANCE REACTION RATES BY LOWERING ACTIVATION ENERGIES FOR REACTIONS.

INCREASING THE “EFFECTIVE CONCENTRATIONS OF ENZYMES

PLACEMENT OF CATALYTIC GROUPS NEAR SUBSTRATE MOLECULES

FAVORABLE ORIENTATION OF SUBSTRATE GROUPS.

CREATION OF COVALENT INTERMEDIATES (LOWERS DELTA G DOUBLE DAGGER)

METAL ION CATALYSIS

ACID OR BASE CATALYSIS (WORKS BEST NEAR THE PKA OF THE DONATING/ACCEPTING GROUP).

COVALENTLY BIND TO ENZYMES TO INHIBIT SUBSTRATE BINDING.

BIND TO ENZYMES IN SUCH A WAY THAT THEIR INHIBITION MAY BE OVERCOME.

• COMPETITIVE INHIBITORS BIND TO THE ENZYME ACTIVE SITE.
• THIS CHANGES KM, BUT NOT VMAX.
• THIS CAN BE OVERCOME BY INCREASING THE SUBSTRATE CONCENTRATION

• NON-COMPETITIVE INHIBITORS BIND TO THE ENZYME, BUT NOT AT THE ACTIVE SITE.
• THIS INDUCES A CONFORMATIONAL CHANGE IN THE ENZYME THAT DISALLOWS SUBSTRATE BINDING.
• THIS LOWERS VMAX
• Km UNCHANGED

BEST TO THINK OF THE MICHAELIS-MENTON EQUATION IN TERMS OF THE ENZYME-SUBSTRATE COMPLEX (E-S)

Vo = Vmax [S] / ([S] + Km)

MICHAELIS MENTON CONSTANT, KM, IS (K2+K3)/K1

THIS CONSTANT IS A MEASURE OF THE BREAKDOWN, OVER THE FORMATION OF, THE ENZYME-SUBSTRATE COMPLEX

SO, HIGH KM INDICATES HIGH RATE OF BREAKDOWN OF E-S, EITHER INTO THE PRODUCT OR BACK TO THE SUBSTRATE.

LOW KM INDICATES HIGH RATE OF E-S FORMATION OF ENZYME AND SUBSTRATE.

THE MORE SUBSTRATE, THE FASTER THE INITIAL VELOCITY.

• DIISOPROPYLPHOSPHOFLUORIDATE (DIPF)
• NERVE GAS REACTS WITH SER ON ACETYLCHOLINE ESTERASE

• TOSYL-L-PHENYLALANINE CHLOROMETHYL KETONE (TPCK)
• SUBSTRATE ANALOG OF CHYMOTRYPSIN

• N,N-DIMETHYLPROPARGYLAMINE (SELEGILINE)
• MONOAMINE OXIDASE (MAO) INHIBITOR

• PENICILLIN
• INHIBITS GLYCOPEPTIDE TRANSPEPTIDASE USED FOR BAC CELL WALLS

• METHOTREXATE
• INHIBITS DIHYDROFOLATE REDUCTASE
• CANCER TREATMENT

BINDS TO ACTIVE SITE

INHIBITION CAN BE REVERSED WITH HIGHER SUBSTRATE [ ]

Km IS INCREASED

Y-INTERCEPT = 1/Vmax

X-INTERCEPT = -1/Km

SLOPE = Km/Vmax