Enzymology: 34 Core Concepts and Principles

Vocabulary practice flashcards covering fundamental enzymology, kinetics, inhibition, regulatory mechanisms, clinical enzymodiagnostics, and hereditary enzymopathies based on the lecture notes.

Enzymes

Biological catalysts, predominantly of protein nature, that accelerate chemical reactions without being consumed, characterized by high specificity, high catalytic activity, strict dependence on specific temperature and pH, and complex, regulatable structures.

Active Center (Active Site)

A specialized region of an enzyme that binds the substrate and carries out the catalytic transformation, composed of a contact (binding) site and a catalytic site.

Contact Site

The specific functional portion of the active center responsible for binding and properly orienting/holding the substrate.

Catalytic Site

The specific functional portion of the active center directly responsible for executing the chemical transformation of the substrate.

"Lock-and-Key" Model (Fischer)

A model stating that the active center possesses a rigid, preformed shape precisely complementary to the substrate, fitting together like a key in a lock.

Induced Fit Model (Koshland)

A dynamic model stating that the active center alters its conformation upon substrate binding to establish an optimal, precise interaction.

Absolute Specificity

The property of an enzyme whereby it catalyzes a reaction for only one single, unique substrate.

Group (Relative) Specificity

The property of an enzyme whereby it acts on a family of structurally related substrates or on a specific type of chemical bond.

Activation Energy

The minimal energy input required to initiate a chemical reaction; lowered by enzymes through substrate proximity, proper molecular orientation, bond strain, and transition state stabilization.

Stages of Enzymatic Catalysis

The three-step catalytic cycle summarized by $E + S \rightleftharpoons ES \rightarrow E + P$, consisting of enzyme-substrate complex ($ES$) formation, substrate-to-product conversion, and product release with free enzyme regeneration.

Cofactors

Non-protein chemical components required by an enzyme for catalytic activity, including inorganic metal ions and organic molecules.

Coenzymes

Organic, low-molecular-weight cofactors required for the catalytic function of specific enzymes.

Prosthetic Group

A cofactor or coenzyme that is tightly or permanently bound to the enzyme structure.

Vitamin-Derived Coenzymes

Biologically active organic cofactors synthesized from vitamins, including $NAD^+$ and $NADP^+$ (Vitamin $B_3$ / PP), FAD and FMN (Vitamin $B_2$), TPP (Vitamin $B_1$), Coenzyme A (Vitamin $B_5$), Pyridoxal phosphate (Vitamin $B_6$), Biotin (Vitamin $B_7$), THF (Vitamin $B_9$), and Cobalamin coenzymes (Vitamin $B_{12}$).

Enzyme Commission (EC) Classification

A systematic classification system dividing all enzymes into 7 major classes based on the chemical reaction type: Oxidoreductases, Transferases, Hydrolases, Lyases, Isomerases, Ligases, and Translocases.

Oxidoreductases

Class 1 enzymes that catalyze oxidation-reduction reactions (e.g., dehydrogenases).

Transferases

Class 2 enzymes that transfer specific chemical functional groups between donor and acceptor molecules (e.g., aminotransferases).

Hydrolases

Class 3 enzymes that cleave chemical bonds via the addition of water (e.g., lipase, amylase, proteases).

Lyases

Class 4 enzymes that cleave chemical bonds without the involvement of water or add chemical groups across double bonds.

Isomerases

Class 5 enzymes that catalyze structural rearrangements converting molecules into their isomeric forms.

Ligases

Class 6 enzymes that catalyze the joining of two molecules coupled with the hydrolysis of high-energy phosphate bonds (ATP expenditure).

Translocases

Class 7 enzymes in the Enzyme Commission (EC) classification system.

Michaelis Constant ($K_m$)

The substrate concentration at which the enzymatic reaction rate reaches half of the maximum velocity ($\frac{1}{2}V_{max}$); serves as a measure of enzyme-substrate affinity, where lower $K_m$ typically signifies higher affinity.

Maximum Velocity ($V_{max}$)

The maximal rate of an enzymatic reaction achieved under complete substrate saturation of all enzyme active sites; directly proportional to total enzyme concentration.

Competitive Inhibition

A form of reversible enzyme inhibition where the inhibitor competes with the substrate for the active site; results in an increased $K_m$, an unchanged $V_{max}$, and can be outcompeted by increasing substrate concentration.

Non-competitive Inhibition

A type of inhibition where the inhibitor binds to an allosteric site distinct from the active site, decreasing catalytic efficiency; results in an unchanged $K_m$ (in pure non-competitive inhibition) and a decreased $V_{max}$.

Uncompetitive Inhibition

A mode of inhibition where the inhibitor binds selectively to the pre-formed enzyme-substrate complex ($ES$); leads to a parallel decrease in both $K_m$ and $V_{max}$.

Irreversible Inhibition

Covalent or extremely stable binding of an inhibitor to an enzyme, permanently abolishing catalytic activity (e.g., aspirin on cyclooxygenase, organophosphates on acetylcholinesterase, penicillin on bacterial cell wall synthesis enzymes).

Organophosphate Toxicity

Pathological mechanism whereby organophosphate compounds irreversibly inhibit acetylcholinesterase, halting acetylcholine breakdown and causing severe synaptic accumulation leading to nervous system overexcitation, convulsions, bronchospasm, and respiratory arrest.

Allosteric Regulation

Modulation of enzyme activity through the binding of non-substrate effector molecules at an allosteric site; allosteric activators enhance activity while inhibitors decrease it (e.g., ATP inhibits and AMP activates phosphofructokinase-1).

Covalent Modification

Post-translational regulation of enzyme activity through the reversible addition or removal of chemical moieties, most commonly phosphorylation (addition of phosphate) and dephosphorylation (removal of phosphate).

Zymogens

Inactive proenzyme precursors that require limited proteolysis (selective peptide bond cleavage) for activation (e.g., pepsinogen converting into pepsin, trypsinogen into trypsin).

Enzyme Induction

An increase in the cellular de novo synthesis of an enzyme stimulated by the presence of a specific inducer molecule.

Enzyme Repression

A regulatory decrease or complete shutoff of enzyme protein synthesis within the cell.

Therapeutic Enzymes

Enzymes administered as medications, such as pancreatin for general digestion, pepsin for protein breakdown, hyaluronidase for connective tissue resorption, and streptokinase for thrombolysis (dissolving blood clots).

Enzymodiagnostics

A clinical diagnostic discipline based on detecting intracellular enzymes released into peripheral blood following cellular membrane disruption to identify the damaged organ and gauge lesion severity.

Diagnostic Reagent Enzymes

Enzymes utilized in vitro as laboratory reagents to quantify biochemical analytes in biological fluids (e.g., glucose oxidase for glucose, urease for urea, cholesterol oxidase for cholesterol).

ALT and AST

Aminotransferase marker enzymes for liver pathology: Alanine aminotransferase (ALT; primarily localized to hepatocytes) and Aspartate aminotransferase (AST; found in liver, heart, and skeletal muscle).

CK and LDH

Enzymatic markers for muscle and myocardial pathology: Creatine kinase (CK, particularly the CK-MB isoenzyme) and Lactate dehydrogenase (LDH), alongside troponin as the primary cardiac infarction marker.

Pancreatic Marker Enzymes

Clinical blood markers for acute pancreatitis consisting of $\alpha$-amylase (starch-cleaving enzyme) and lipase (fat-cleaving enzyme, which exhibits superior diagnostic specificity).

Isoenzymes (Isozymes)

Multiple molecular variants of a single enzyme that catalyze the identical chemical transformation but differ in quaternary structure, physical properties, and tissue distribution (e.g., CK-MB in myocardium).

Enzymopathies

Pathological conditions arising from defective activity or complete deficiency of specific enzymes; classified into hereditary (genetic mutations) and acquired forms (diseases, toxic exposures, or vitamin deficiencies).

"One Enzyme — One Disease" Principle

The concept that the dysfunction or deficiency of a single specific enzyme causes a discrete, defined pathological disorder (e.g., phenylketonuria via phenylalanine hydroxylase; alkaptonuria via homogentisate oxidase; galactosemia via galactose metabolism enzymes; Tay-Sachs disease via hexosaminidase A).