BCM 1.2 - Enzyme Properties and Functions: Substrate Binding, Enzyme Kinetics, Enzyme Regulation and Inhibition

Vocabulary practice flashcards covering general characteristics, classification, specificity, catalytic mechanisms, factors, kinetics, regulation, and medical applications of enzymes based on Module 1.2.

Simple Enzyme

An enzyme composed entirely of protein without any non-protein components.

Holoenzyme

A complete, catalytically active complex enzyme consisting of a protein part (apoenzyme) and a non-protein part (cofactor).

Apoenzyme

The protein component of a holoenzyme.

Cofactor

The non-protein component of a holoenzyme required for enzyme catalytic activity.

Prosthetic Group

A cofactor consisting of a small inorganic molecule or metal ion that is tightly bound to the apoenzyme.

Coenzyme

A cofactor consisting of a large organic molecule, such as a vitamin derivative, that is loosely bound to the apoenzyme.

Energy of Activation ($E_a$)

The minimum energy required to initiate a chemical reaction, which is lowered by enzymes to accelerate reaction rates.

Oxidoreductases

Class 1 enzymes that catalyze oxidation and reduction reactions involving the transfer of electrons, charges, or hydrogen ions ($H^+$).

Transferases

Class 2 enzymes that transfer chemical groups from one molecule to another, or within a single molecule.

Hydrolases

Class 3 enzymes that cleave substrate molecules by breaking chemical bonds in the presence of water.

Lyases

Class 4 enzymes that split molecules via a nonhydrolytic process without using water, leaving double bonds or adding groups to double bonds.

Isomerases

Class 5 enzymes that interconvert isomeric molecules by catalyzing intramolecular rearrangements.

Ligases

Class 6 enzymes that join two molecules together, creating bonds at the expense of a nucleoside triphosphate such as ATP.

Constitutive Enzyme

An enzyme present in constant amounts within a cell regardless of metabolic conditions or substrate levels.

Inducible Enzyme

An enzyme whose cellular concentration is increased in response to the presence of a specific substrate.

Active Site

A specific three-dimensional cleft, cavity, or crevice on an enzyme that binds substrates and cofactors to catalyze a chemical reaction.

Lock-and-Key Model

A rigid template model proposed by Emil Fischer in 1894 asserting that the active site has a pre-formed complementary 3D surface for its substrate.

Induced Fit Model

A flexible model proposed by Daniel E. Koshland Jr. in 1958 stating that substrate binding induces a conformational change in the enzyme active site to align catalytic groups.

Proximity and Orientation Effects

A catalytic mechanism where the enzyme positions reacting groups close together in the correct alignment to favor product formation.

Desolvation Effects

A catalytic mechanism involving the removal of surrounding water molecules from the substrate as it moves into a hydrophobic active site pocket.

Acid-Base Catalysis

A catalytic mechanism where active site amino acid side chains act as proton donors and proton acceptors.

Covalent Catalysis

A catalytic mechanism where nucleophilic amino acid side chains attack electrophilic substrate atoms to form a temporary covalent intermediate.

Strain Effects

A catalytic mechanism where conformational changes upon substrate binding induce distortion or strain on reactive bonds, facilitating product formation.

Metal Coordination Effects

A catalytic mechanism where bound metal ions act as Lewis acids (electrophiles) to stabilize negative charges, promote nucleophilic attack, or form bridge complexes.

Irreversible Inhibitors

Inhibitors that bind tightly via covalent or noncovalent bonds to an enzyme, leading to permanent loss of functional conformation and catalytic activity.

Competitive Inhibitor

A reversible inhibitor that structurally resembles the substrate and competes for binding at the active site, increasing $K_m$ while leaving $V_{\text{max}}$ unaffected.

Noncompetitive Inhibitor

A reversible inhibitor that binds to an allosteric site distinct from the active site, decreasing $V_{\text{max}}$ while leaving $K_m$ unaffected.

Uncompetitive Inhibitor

A reversible inhibitor that binds exclusively to the enzyme-substrate ($ES$) complex, reducing both $K_m$ and $V_{\text{max}}$.

Enzyme Activity

The quantity of enzyme activity that catalyzes the conversion of $1\,\mu\text{mol}$ of substrate per minute under specified conditions.

Specific Activity

The enzyme activity expressed per milligram of enzyme protein ($\mu\text{mol}\,\text{min}^{-1}\,\text{mg}^{-1}$).

Katal (kat)

The SI unit of enzyme activity representing the transformation of $1\,\text{mol}$ of substrate per second.

Turnover Number ($k_{\text{cat}}$)

The maximum number of substrate molecules converted to product per unit of time by a single fully saturated enzyme molecule.

Michaelis Constant ($K_m$)

The substrate concentration at which initial reaction velocity ($V_0$) is equal to half of maximum velocity ($\frac{1}{2}V_{\text{max}}$), measuring substrate binding affinity.

Lineweaver-Burk Plot

A linear double-reciprocal plot of $\frac{1}{V_0}$ versus $\frac{1}{[S]}$ with slope $\frac{K_m}{V_{\text{max}}}$, y-intercept $\frac{1}{V_{\text{max}}}$, and x-intercept $-\frac{1}{K_m}$.

Eadie-Hofstee Plot

A plot of reaction velocity $v$ against $\frac{v}{[S]}$ that avoids data point compression at lower substrate concentrations.

Ordered Sequential Reaction

A multi-substrate sequential reaction mechanism requiring a strict, obligatory sequence of substrate binding and product release.

Random Sequential Reaction

A multi-substrate sequential reaction mechanism where substrates can bind and products can be released in any arbitrary order.

Ping-Pong Reaction

A multi-substrate mechanism where one or more products are released before all substrates bind, interconverting the enzyme between two distinct forms ($E$ and $F$).

Allosteric Effector

A regulatory substance that binds to an enzyme at a site physically distinct from the catalytic site, altering enzyme conformation and activity.

Positive Allosteric Effector

An effector that binds to an activator site and induces a conformational change that increases enzyme affinity for substrate.

Negative Allosteric Effector

An effector that binds to an inhibitory site and induces a conformational change that decreases enzyme affinity for substrate.

K Class Allosteric Enzyme

An allosteric enzyme whose effector alters the Michaelis constant ($K_m$) without changing maximum velocity ($V_{\text{max}}$).

V Class Allosteric Enzyme

An allosteric enzyme whose effector alters maximum velocity ($V_{\text{max}}$) without changing the Michaelis constant ($K_m$).

Homotropic Interaction

An allosteric effect in an oligomeric protein where the binding of a substrate molecule to one subunit influences the binding of the same substrate to other subunits.

Heterotropic Interaction

An allosteric effect where the binding of one specific molecule influences the binding of a different molecule or substrate to the enzyme.

Reversible Covalent Modification

Enzyme regulation through the reversible covalent attachment and hydrolytic removal of chemical groups, such as phosphorylation and dephosphorylation.

Calmodulin

A eukaryotic calcium-binding control protein that senses intracellular calcium levels and activates target enzymes upon binding.

Zymogen

An inactive enzyme precursor (proenzyme) activated irreversibly by hydrolytic cleavage of specific peptide bonds.

Isoenzymes

Physically distinct forms of the same enzyme that catalyze the same chemical reaction but differ in chemical properties, structure, and substrate affinity.

Streptokinase

A therapeutic enzyme used clinically to dissolve blood clots in acute myocardial infarction and deep venous thrombosis.

Asparaginase

A therapeutic enzyme administered as an antineoplastic agent in the treatment of certain types of leukemia.