Enzyme Kinetics, Regulation, and Vitamins

Comprehensive vocabulary flashcards covering enzyme kinetics, types of allosteric and competitive regulation, pharmaceutical enzyme inhibitors, and vitamin-derived coenzymes.

Avogadro's Number

The number of units in one mole of any substance, approximately equal to $6.02 \times 10^{23}\,\text{molecules/mole}$.

Catalase

One of the most efficient enzymes known, capable of decomposing $H_2O_2$ at a rate of up to $10^7$ catalytic events per second.

Enzyme-Substrate (ES) Complex

The intermediate complex formed when an enzyme binds to its substrate, within which the chemical catalysis reaction takes place before releasing products.

Enzyme Saturation

The state reached at high substrate concentration ($[S]$) where the reaction rate reaches a plateau and cannot increase further because all enzyme active sites are occupied.

Pepsin

A digestive enzyme operating in the acidic environment of the stomach that initiates protein digestion, exhibiting an optimum activity at $\text{pH } 2$.

Trypsin

A digestive enzyme that functions in the alkaline environment of the small intestine, exhibiting an optimum activity at $\text{pH } 8$.

Activation

Any regulatory process that starts or increases the catalytic action of an enzyme.

Inhibition

Any regulatory process that slows down or completely stops the catalytic action of an enzyme.

Feedback Control

A regulatory mechanism in which the end product of a metabolic pathway inhibits an enzyme near the beginning of that pathway to prevent the wasteful synthesis of excess compounds.

Allosteric Control

A regulatory mechanism where the binding of an effector molecule at one site on an enzyme influences its affinity or catalytic activity at a distinct, different site.

Positive Allosteric Regulator

An allosteric effector that binds to a non-active site and alters the active site conformation so that the enzyme becomes a more effective catalyst, accelerating the reaction rate.

Negative Allosteric Regulator

An allosteric effector that binds to an enzyme and alters active site geometry to make it a less effective catalyst, slowing down the reaction rate.

Reversible Inhibition

A form of enzyme inhibition in which the inhibitor binds non-covalently and can dissociate, restoring full enzymatic activity.

Irreversible Inhibition

A form of enzyme inhibition where an inhibitor binds permanently (often covalently) to the enzyme, resulting in a permanent loss of catalytic activity.

Competitive Inhibitor

An inhibitor that structurally resembles the substrate and competes for binding at the active site; its inhibitory effect can be overcome by high concentrations of substrate ($[S]$).

Non-Competitive Inhibitor

An inhibitor that binds to an allosteric site rather than the active site, decreasing $V_{\text{max}}$ by preventing a required conformational change; it cannot be overcome by high substrate concentrations.

Statins

Antihyperlipidemic drugs that act as competitive inhibitors and structural analogs of HMG-CoA, binding the active site of HMG-CoA reductase to inhibit de novo cholesterol synthesis.

Aspirin (Acetylsalicylate)

An analgesic and antipyretic NSAID that irreversibly inhibits cyclooxygenase (COX) through covalent modification, transferring an acetyl group ($-\text{COCH}_3$) to a serine residue.

Prostaglandins (PGs)

Potent, short-lived, short-range lipid hormones derived from essential fatty acids via the cyclooxygenase (COX) pathway that regulate inflammatory responses.

COX-1

A cyclooxygenase isoform that produces thromboxane, promoting platelet clumping and vasoconstriction.

COX-2

A cyclooxygenase isoform that produces prostacyclin, which reduces platelet aggregation and vasoconstriction.

Vioxx

An NSAID that selectively inhibits COX-2 but not COX-1, decreasing prostacyclin while maintaining thromboxane levels, thereby causing increased vasoconstriction, platelet clumping, and cardiovascular risk.

Zymogen (Proenzyme)

An inactive precursor of an enzyme that requires proteolytic cleavage of part of its polypeptide chain to yield an accessible active site.

Protein Kinase

An enzyme that catalyzes the covalent transfer of a phosphate group from $\text{ATP}$ to a target protein to regulate its catalytic state.

Protein Phosphatase

An enzyme that hydrolytically removes a covalently attached phosphate group from a target protein, reversing the action of a protein kinase.

Genetic Control

A regulation strategy where the amount of enzyme is controlled by turning the transcription and synthesis of its encoding gene on or off as needed, such as lactose inducing $\beta$-galactosidase in E. coli.

Water-Soluble Vitamins

Nutrients including vitamin C and the eight B vitamins that cannot be stored in the body and predominantly function as components of enzyme coenzymes.

Fat-Soluble Vitamins

Vitamins A, D, E, and K, which are stored in adipose tissue and do not function as coenzymes.

Coenzyme

A low-molecular-weight organic molecule, typically derived from dietary vitamins, that associates with an enzyme to facilitate catalytic transformations.

Niacin

A water-soluble B vitamin that serves as the precursor for coenzymes $\text{NAD}^+$ and $\text{NADP}^+$, functioning in redox reactions converting alcohols to carbonyls.

Riboflavin (Vitamin $B_2$)

A water-soluble vitamin that forms the functional redox coenzymes $\text{FAD}$ and $\text{FMN}$, which mediate the conversion of alkanes to alkenes.

Thiamine (Vitamin $B_1$)

A water-soluble B vitamin precursor to thiamine pyrophosphate ($\text{TPP}$), which functions metabolically in the transfer of 2-carbon fragments.

Pantothenate

A water-soluble B vitamin incorporated into Coenzyme A ($\text{CoA}$), where it functions in the metabolic transfer of acyl groups.

Pyridoxine (Vitamin B)

A water-soluble vitamin precursor to pyridoxal phosphate, an essential coenzyme for the transfer of amino groups.

Folate

A water-soluble vitamin converted into the coenzyme tetrahydrofolate, which is responsible for the metabolic transfer of 1-carbon fragments.

Biotin

A water-soluble vitamin that is covalently linked to carboxylases and functions to fix carbon dioxide without undergoing any structural change from its dietary form.

Vitamin C (Ascorbic Acid)

A water-soluble vitamin that is biologically active in the body without requiring any chemical modification or incorporation into a larger coenzyme.

Nicotinamide Adenine Dinucleotide ($\text{NAD}^+$)

A redox coenzyme that collects two electrons and a proton when carbon substrates are oxidized, storing chemical reducing power as $\text{NADH}$.

Flavin Adenine Dinucleotide ($\text{FAD}$)

A redox coenzyme derived from riboflavin containing a flavin, ribitol, and ADP unit that undergoes a two-electron reduction to form $\text{FADH}_2$.

Vitamin D

A fat-soluble vitamin synthesized in the skin upon exposure to sunlight that aids in intestinal calcium uptake.

Vitamin K

A fat-soluble vitamin essential for the maintenance of bone and the synthesis of blood clotting factors.