Chapter 8. Enzymes: Basic Concepts and Kinetics Flashcards
the energy required to form the transition state from the substrate of a reaction.
Free energy ofactivation
a reaction involving multiple substrates in which one or more products are released before all substrates bind the enzyme. The defining feature of these reactions is the formation of a substituted-enzyme intermediate.
double-displacement (ping-pong)
antibodies generated by using transition-state analogs of a particular reaction as antigens. Such antibodies often function as catalysts for the reaction.
catalytic antibody (abzyme)
A tightly bound cofactor required for a protein's activity
Prosthetic group
a small organic molecule required for the activity of many enzymes; vitamins are often components of coenzymes.
Coenzyme
form of energy capable of doing work under conditions of constant temperature and pressure. Also, a measure of the usable energy generated in a chemical reaction; denoted by the symbol G in thermodynamics. The change in free energy (delta G) of a system undergoing transformation at constant pressure is equal to the change in enthalpy (delta H) minus the product of the absolute temperature (T) and the change in entropy (delta S).
Free energy
the reduction in the rate of enzyme activity observed when the enzyme can bind the substrate and the inhibitor simultaneously. Noncompetitive inhibitors decrease the turnover number for an enzyme but do not diminish the proportion of enzyme molecules bound to the substrate; their effects are not overcome by increasing substrate concentration.
noncompetitive inhibition
A reactant in a chemical reaction. An enzyme catalyzes a single chemical reaction or set of closely related reactions, and the components of those reactions are called substrates
Substrate
the reduction in the rate of enzyme activity observed when the enzyme can bind the substrate or the inhibitor but not both. Many competitive inhibitors resemble the substrate and compete with it for binding to the active site. Relief from inhibition by saturation with substrate is a kinetic hallmark of competitive inhibition.
competitive inhibition
a specific region of an enzyme that binds the substrate and carries out catalysis.
Active site
A bisubstrate reaction in which both substrates must bind to the enzyme before any product is released. Consequently, a ternary complex of the enzyme and both substrates is a reaction intermediate
sequential reaction
Inhibition that results when an enzyme converts a pseudosubstrate into a reactive inhibitor that immediately inactivates its catalytic activity.
mechanism-based (suicide) inhibition
the concentration of substrate at which half the active sites of an enzyme are filled.
KM (the Michaelis constant)
an enzyme that consists of the protein component forming the main body of the enzyme (the apoenzyme) and any necessary, usually small, cofactors.
Holoenzyme
biological macromolecules that act as catalysts for biochemical reactions; while almost all are composed of protein, catalytically active RNA molecules have also recently been discovered.
Enzyme
