Enzyme Properties, Kinetics, Regulation, and Clinical Applications

Comprehensive flashcards covering enzyme classification, active site models, kinetics equations (Michaelis-Menten, Lineweaver-Burk), inhibition mechanisms, regulatory pathways, and medical applications.

What is the structural difference between simple enzymes and holoenzymes?

Simple enzymes consist strictly of proteins, whereas holoenzymes (complex or conjugated enzymes) consist of a protein part (apoenzyme) and a non-protein part (cofactor).

How do prosthetic groups differ from coenzymes?

A prosthetic group is typically a small inorganic molecule or ion tightly bound to the apoenzyme, whereas a coenzyme is a large organic molecule (often derived from vitamins) loosely bound to the apoenzyme.

What is the molecular weight range of enzymes?

Enzymes range in molecular weight from $10\,\text{kD}$ to $1,000\,\text{kD}$.

By how much do enzymes typically increase chemical reaction rates, and by what mechanism?

Enzymes increase reaction rates by $10^5$ to $10^{12}\text{-fold}$ by lowering the activation energy ($E_a$) of the reaction.

What function is catalyzed by Class 1: Oxidoreductases?

They catalyze oxidation and reduction reactions, involving the transfer of electrons, charges, and hydrogen ($\text{H}^+$) ions.

How do Class 4: Lyases differ from Class 3: Hydrolases in their mechanism of cleavage?

Class 3: Hydrolases cleave molecules in the presence of water, whereas Class 4: Lyases split molecules via a nonhydrolytic process (without water), leaving double bonds or adding groups to double bonds.

What do the four numbers in an Enzyme Commission (EC) classification number signify?

The 1st number indicates the general class, the 2nd indicates the subclass, the 3rd indicates the sub-subclass, and the 4th specifies the complete name in the list (e.g., Glucokinase EC 2.7.1.2).

What is the distinction between constitutive and inducible enzymes?

Constitutive enzymes are present in constant amounts within the cell, while inducible enzyme presence is induced by a specific substrate when needed.

Who proposed the Lock-and-Key Model and the Induced Fit Model of active site interaction?

The Lock-and-Key Model was postulated by Emil Fischer in 1894, and the Induced Fit Model was postulated by Daniel E. Koshland Jr. in 1958.

What occurs during the desolvation effect in enzymatic catalysis?

Water molecules surrounding the substrate dissociate from it, sequestering the substrate inside an immobilized hydrophobic environment within the active site to accelerate the reaction.

How are enzyme activity and specific activity defined and expressed?

Enzyme activity is defined as $\mu\text{mol substrate/min}$, representing the micromoles of substrate transformed per minute. Specific activity is expressed as $\mu\text{mol substrate/min/mg enzyme}$.

What is the catalytic constant ($K_{cat}$) or turnover number?

It is expressed as $\mu\text{mol substrate/min/}\mu\text{mol enzyme}$, representing the number of substrate molecules converted to product per unit time on a single fully saturated enzyme molecule.

What is the Briggs and Haldane Steady State Assumption?

It posits that the concentration of the enzyme-substrate complex ($[ES]$) remains constant during the initial velocity phase ($V_0$) because the rate of $[ES]$ formation equals its rate of breakdown.

How is the Michaelis constant ($K_m$) defined, and what does a high $K_m$ value indicate?

The Michaelis constant ($K_m$) is the substrate concentration at which initial velocity ($V_0$) is $\frac{1}{2} V_{\max}$. A high $K_m$ indicates weak enzyme-substrate binding (low affinity).

What do the slope, y-intercept, and x-intercept represent in a Lineweaver-Burk double-reciprocal plot?

The slope represents $\frac{K_m}{V_{\max}}$, the y-intercept represents $\frac{1}{V_{\max}}$, and the x-intercept represents $-\frac{1}{K_m}$.

How do competitive, noncompetitive, and uncompetitive inhibitors affect $K_m$ and $V_{\max}$?

Competitive inhibitors increase $K_m$ while $V_{\max}$ is unaffected; noncompetitive inhibitors leave $K_m$ unaffected while reducing $V_{\max}$; uncompetitive inhibitors reduce both $K_m$ and $V_{\max}$.

What defines a Ping-Pong reaction mechanism according to Cleland notation?

Intermediate products are released before all substrates are bound, and the enzyme alternates between two distinct structural forms ($E$ and $F$ forms), as demonstrated by transaminases.

What is the difference between K-class and V-class allosteric enzymes?

K-class allosteric effectors alter $K_m$ without changing $V_{\max}$, whereas V-class allosteric effectors alter $V_{\max}$ without changing $K_m$.

What is Calmodulin and how does it regulate enzyme activity?

Calmodulin is a calcium-binding protein in eukaryotes that senses intracellular calcium concentrations and activates target enzymes upon binding to them.

What are zymogens or proenzymes, and how are they activated?

They are inactive enzyme precursors converted irreversibly into active forms through proteolytic activation (hydrolysis of specific peptide bonds), such as pepsinogen.

Which serum enzyme levels are elevated in acute pancreatitis, particularly with hypertriglyceridemia ($>500\,\text{mg/dL}$)?

Pancreatic amylase and pancreatic lipase.

Which enzyme isoenzyme peaks during the 1st to 2nd day following a myocardial infarction?

Creatine Kinase-MB ($\text{CK-MB}$).

What are the therapeutic applications of Streptokinase and Asparaginase?

Streptokinase is used to clear blood clots in myocardial infarction and Deep Venous Thrombosis (DVT), while Asparaginase is used as a therapeutic drug in certain types of leukemia.

Which immobilized enzyme is used on commercial glucometer test strips to measure blood glucose?

Glucose oxidase.