Enzyme Regulation – Lecture Review

Seventeen vocabulary flashcards summarizing the major terms and definitions related to enzyme regulation, allosteric control, phosphorylation, zymogen activation, and blood-clotting cascades discussed in the lecture.

Enzyme Regulation

Allosteric binding, reversible covalent modification, regulatory proteins, and proteolytic cleavage

Allosterism

Reversible, non-covalent binding of regulatory compounds: allosteric modulators/ effectors

Allosteric enzymes

Undergo conformational changes in response to modulator binding; modulator binds to regulatory subunit, leading to a conformational change in the catalytic subunit, increasing activity

Homotropic Modulator

A molecule that is both the substrate and the allosteric modulator of an enzyme

Heterotropic Modulator

An allosteric effector that is chemically distinct from the enzyme’s substrate and alters activity upon binding.

Aspartate Transcarbamoylase (ATCase)

Catalyzes the conversion of carbamoyl phosphate + aspartate to carbamoyl aspartate, an early step in pyrimidine biosynthesis

CTP (Cytidine Triphosphate)

An allosteric regulator of ATCase that causes the catalytic trimers to come together, causing it to become more T-like, or less active

ATP (Adenosine Triphosphate)

An allosteric regulator of ATCase that causes catalytic trimers to move apart, making it more R-like or more active.

Cooperative Kinetics

Sigmoidal V₀ vs [S] behavior of many allosteric enzymes, where small increases in substrate produce large activity changes due to subunit–subunit communication.

Protein Kinase

Catalyze the attachment of phosphoryl groups to amino acid residues with ATP. (Ser, Tyr, Thr, His)

Phosphoprotein Phosphatase

Removes phosphoryl groups from target residues Ser, Tyr, Thr, His.

Glycogen Phosphorylase

Muscle enzyme that cleaves glycogen to release glucose-1-phosphate; activated (phosphorylase a) by phosphorylation and inactivated (phosphorylase b) by dephosphorylation.

Zymogen

An inactive enzyme precursor that is cleaved to form active protease enzyme (proprotein or proenzyme); “-ogen”, “pre-”, “pro-”

Trypsinogen, chymotrypsin

Pancreatic zymogens that are activated in the small intestine to form trypsin and chymotrypsin

Pepsinogen

Stomach zymogen that is activated to form pepsin

Intrinsic Pathway (Clotting)

Blood-coagulation cascade initiated by internal vascular damage. Involves all components in blood plasma

Extrinsic pathway (blood clotting)

Involves protein tissue factor (TF), which is not found in the blood but in cells surrounding the vasculature. Pathway is activated by an injury to the vessel