Chapter 4: Enzyme Kinetics Flashcards
Enzyme kinetics
- Investigation of rates of enzyme-catalyzed reactions
- Help determine substrate specificity and reaction mechanisms
Establishes the initial rate of reaction
- Measuring either the disappearance of substrate or the appearance of product per unit time
Progressive curve
- The time course of an enzyme-catalyzed reaction
- Concentration on y-axis
- Time on x-axis
Maximum velocity of enzyme (Vmax)
- The point where the enzyme the enzyme is saturated with substrate (all enzyme in ES form) and very little free enzyme exists
Initial reaction rates (Vo)
- Measured by drawing a tangent to the hyperbolic plot of [product] formed vs time when t = 0
Progress cruve (Vo) is at maximum
- Substrate supplies are high and a minimal amount of product has been formed
- Makes reverse reaction insignificant
High enzyme concentration effect on initial rate
- Initial rate will be higher at high enzyme concentration than at low enzyme concentration
- More product is formed as time increases for each enzyme when substrate is in excess
Gradient of slope
- Calculates the amount of product formed per unit time
Calculate initial rate (Vo)
- Can be determined by measuring the gradient at t = 0
First order kinetics
- At low concentrations or substrate, a rapid increase in reaction velocity that is proportional to [S] is observed
Zero order kinetics
- At high [S] the curve plateaus at a maximum value (Vmax)
- Reaction velocity is independent of changes in [S]
Temperature
- Reaction rate initially increases when this increases as the enzyme is activated
Denaturation of the enzyme
- Occurs when the non-covalent stabilizing factors of an enzyme are broken
- Reaction rate declines as the temperature is further increased
- Native conformation of the enzyme is disrupted
pH
- Measure of [H+] of a solution
- (-) log [H+] = log 1/[H+]
Functional groups
- Side chains of amino acids
- Can function as weak acids
- Perform acid/base interactions
- Degree of ionization changes as pH fluctuates
Interstitial fluid buffer system
- Carbonic acid - Bicarbonate
- Hydrogen phosphate
- Proteins
Intracellular fluid buffer system
- Carbonic acid - Bicarbonate
- Hydrogen phosphate
- Proteins
Blood buffer system
- Carbonic acid - Bicarbonate
- Hemoglobin
- Hydrogen phosphate
- Plasma proteins
Acidosis
- pH of blood falls
- Common in poorly controlled diabetes mellitus
Protects against acidosis
- Carbonic acid - bicarbonate buffer system of the blood
Alkalosis
- pH of the blood becomes elevated above 7.4
- May occur with extended periods of vomiting or from hyperventilation
Hydrogen phosphate - dihydrogen phosphate buffer system
- Works in the cytoplasm of most cells
Gastric pepsin
- Secreted from the chief cells in gastric glands
- Optimal pH of 1.5
Michaelis constant (Km)
- The substrate concentration at which the initial velocity is 1/2 Vmax (half the enzyme active sites are occupied)
Y-intercept of LWB
1/Vmax
X-intercept of LWB
-1/Km
Gradient/slope of LWB
Km/Vmax
Enzyme Kinetics
- The study of the initial rates (Vo) of enzyme-catalyzed reactions
Plotting of Vo vs [S] or an enzyme-catalyzed reaction yields:
- A classic hyperbolic plot for enzymes that exhibit M/M kinetics
Michaelis constant (Km)
- The substrate concentration at which the reaction rate is half maximal
Lower Km
- Higher enzyme’s affinity for susbtrate
Changes in temperature and pH
- Can alter enzyme activity
