4 - Enzymology Flashcards
What is enzymology and what does it aim to achieve?
Enzymology is the study of enzymes in action.
The aim is to relate quantitatively the contributions of substrate concentration, pH, temperature, ionic strength, etc to the reaction rate.
What are 2 things that kinetic information is vital for?
- Predicting how a given enzyme will behave and respond in various situations and conditions, and thus how much product it will produce.
- Diagnosing the mechanisms of inhibitor and effector actions.
When enzyme reaction rates are measured experimentally what is the velocity of the reaction proportional to and why?
The reaction velocity is directly proportional to the starting concentration of the enzyme [E0]
This is because the initial substrate concentration [S0] is usually very high relative to that of the enzyme.
When enzyme reaction rates are measured experimentally and enzyme concentration is fixed, what occurs at a low, medium, and high [S]?
At low [S]: Reaction velocity proportional to [S] - first order rate with respect to the substrate.
At medium [S]: Reaction velocity rises slower, no longer proportional to [S] - mixed order rate with respect to the substrate.
High [S] Rate becomes constant and independent of [S], enzyme is saturated with substrate - reaction is zero order.
In Michaelis and Menten’s theory on enzyme kinetics what was the critical feature of the theory and what 3 assumptions must be made?
Critical feature: A specific ES complex is an obligatory intermediate in the catalysis.
Assumptions:
- [E0] very small compared to [S0], [S is not significantly depleted].
- The product concentration is effectively zero at the start of the reaction and over the time the initial rate is measured.
- The product-releasing step is much slower than the release of S from ES. (E and S come to equilibrium with ES).
What is the Michaelis equation and what do the shorthand components of the equation represent?
V0 = Vmax x [S0] / Km + [S0]
V0 - Initial velocity.
Vmax - Maximum velocity which the enzyme is capable.
[S0] - initial substrate concentration.
Km - Michaelis constant.
What does Km represent and if the Michaelis-Menten assumptions are valid what does the Km value suggest?
Km is numerically equal to the [S] that provides half the Vmax.
Km is also an indicator of the strength of binding or affinity of the substrate for the enzyme.
If assumptions are correct, tightly bound substrates has a low Km and loosely bound substrates have a high Km.
What does the value of Vmax also represent/ equate to besides the maximum velocity?
