temperature, pH, enzyme concentration and substrateconcentration
What is the shape of a temperature vs velocity graph?
What is the shape of a pH vs velocity graph?
What is the shape of an enzyme concentration vs velocity graph?
Steady State Assumption?
the rate of ES formation is equal to the rate of ES breakdown
Michaelis Menten equation
Vmax = maximum velocity of the enzyme (enzyme saturated with substrate)
Km= concentration at 1/2 Vmax
What is kcat
turnover number of the enzyme (# of substrate molecules converted to product per unit time under saturating conditions)
The Lineweaver-Burk Plot
•Inhibitor binds only to free enzyme (E) not (ES)
•Substrate cannot bind when I is bound at active site
•Vmax is the same but apparent Km (Kmapp) is increased
•Competitive inhibitors usually resemble the substrate
•Uncompetitive inhibitors bind to ES not to free E
•Vmax decreased by conversion of some E to ESI
•Km (Kmapp) is also decreased
•Lines on double-reciprocal plots are parallel
•mixed inhibitors bind to both E and ES
•Inhibitors do not bind at the same site as S
•Vmax decreases, Km does not change
•Inhibition cannot be overcome by addition of S
form stable covalent bonds with the enzyme or destroy an essential functional group of the enzyme
initially unreactive but after the first few steps of the catalytic mechanism are converted to a reactive species that inactivates the enzyme (Biochemical trojan horses)
-Digestive enzymes,including trypsin, chymotrypsin,and elastase,that cleave peptide bonds in protein substrates
-Are synthesized and stored in the pancreas as inactive zymogens to prevent damage to cellular proteins
-Catalytic Mechanism contains elements of covalent and acid-base catalysis
-an inactive enzyme precursor
-activated at the appropriate time by selective proteolysis.
Where does trypsin cleave
by Lys and Arg
Where does Chymotryposin cleaves?
by Phe and Tyr
Where does Elastase cleave?
by Gly and Ala
a chemical species that donates an electron-pair to an electrophile to form a chemical bond in a reaction
Serine Protease steps
Stage 1 Cleaving the Substrate
Histidine acts as a base to extract proton from hydroxyl group of Ser.
The activated hydroxyl group of Serine forms a covalent linkage to the carbonyl group of the peptide bond to be cleaved.
Histidine acts as an acid to donate a proton to the amide group of the peptide bond to be cleaved.
Stage 2 Regenerating the Enzyme
Histidine acts as a base to extract proton from hydroxyl group of a water molecule.
The water molecule attacks the point of covalent linkage between the enzyme and substrate.
Histidine acts as an acid to donate the proton extracted from the water molecule to reform the hydroxyl group of the Serine.
What are the two types of enzyme activity Regulation?
-phosphorylation, methylation, glyosylation
non-covalent modification (allosteric)
-binding of a regulatory, allosteric molecule to a site on the enzymedistinct from the active site to modulate enzyme activity
What point of a reaction pathway would be logical to have regulatory enzymes?
the enzyme catalyzing the first committed reaction
1) Activities regulated by interaction with metabolic intermediates.
2) Allosteric modulators bind non-covalently to the enzymes at sites distinct from the active site. (Substrates and activatorsmay bind only to the R state while inhibitors may bind only to the T state)
3) Allosteric enzymes usually are quaternary structures.
4) Allosteric enzymes do not obey Michaelis-Menten kinetics, have sigmoidal curves.