BC 11 Enzyme Kinetics

Question 1

Velocity/Substrate graphs

Answer 1

same amount of enzyme in all cases

enzyme catalyzed reaction: hyperbolic curve:

Michaelis Menten Kinetics

Question 2

Michaelis Menten

Answer 2

Vmax= maximal velocity of the reaction (saturated with substrate)

Vo=Vmax/(Km+s)

Km=Vmax/2 substrate concentration where the initial velocity of the reaction is half the maximum

1. rate of reaction is the initial velocity
2. concentration of substrate greater than concentration of eznyme
3. rate of formation of the ES is equal to the rate of breakdown of ES to E+P. ES transient

Question 3

interpreting MM

Answer 3

when [S] &laquo_space;Km, the velocity of the reaction is proportional to the substrate concentration

when [S] = Km Vo=Vmax/2

when [S]&raquo_space; Km the ensyme is saturated with substrate and V unaffected by substrate increase

Question 4

Vmax & Km

Answer 4

Vmax: Sturated
NOT a constant, will increase with more enzyme
If enzyme concentration is halved, the initial ate of reaction Vo and Vmax are reduced by half. (and double)

Kcat: turnover constant: enzyme efficiency =Vm/E

Km: measure of binding affinity. Inversly prop to the affinit of the enzyme.

• low KM=low affinity for substrate.
• how much substrate is needed to fill HALF of enzyme

if enzymes require a high [S] to acheive Vmax/2 then they fall off easy and have high Km

Question 5

Hexokinase/Glucokinase

Answer 5

both catalyze teh same reaction:
Glucose + ATP -> Glucose6Phosphate + ADP

Glucokinase: love and Bcells of Panc. HIGH Km
-activity is low and dramatically increases when blood glucose is high (prevent hyperglycemia)

Hexokinase: in most tissues LOW Km

• enzyme activity is constant under most glucose concentrations, does not change
• in brain, need energy from glucose
• still activate in fasting state

Question 6

Lineweaver/Burk

Answer 6

easier method to determine Vmax and Km, linear
1/Vo to 1/[S]
1/Vo=Km/Vmax+1/Vmax
WHAT SHOULD WE BE ABLE TO DO WITH THIS

Question 7

Reversible Inhibitors

Answer 7

metal ions, drugs, toxins

Reversible: Non covalent bond, removes when dilute

-Competetive:statin drugs for cholesterol synthesis
or ethanol to alcohold dehydrogenase for formeldahyde (formed from methanol and ethylene glycol -antifreeze)
*tend to resemble structure of substrate
*compete for active site
*Vmax unaffected (overcome by excess [S])
*Apparent Km increased(takes longer to fill half enzyme)

• Non competetive:
• different site binding change conformation
• no resemblance to substrate
• decreases Vmax (less available enzyme)
• Km unaffected. Just less enzyme, wont change the function

allosteric: DIFFERENT, physio rols, modify vmax K0.5 , only affect allosteric enzymes

Question 8

irreversible inhibitors

Answer 8

Covalent bonds, permanent loss of catalytic activity. TOXIC
R groups of amino acid residues, or heave metals, insecticides
typically to active site
*pennicilin and aspirin, acetylates key serine residue on cyclooxygenases

scuicide inhibitors:

• cannot bind to active site in ingested form
• must be modified
• unreactive until within targets area
• Disulfram: blocks oxidation of acetylaldehyde to acetate by inhibiting aldehyde dehydrogenase. accumulation of acetalaldehyde causes nasea and hyperventilation (addicts)