Enzyme from bishops

Enzyme

protein that catalyzes a biochemical reaction without being consumed; contains an active site and may require cofactors.

Apoenzyme

The protein portion of an enzyme without its nonprotein cofactor.

Cofactor

Nonprotein component required for enzyme activity; can be inorganic (activators) or organic (coenzymes).

Coenzyme

An organic nonprotein molecule that assists enzyme activity; NAD+/NADH are common examples.

Prosthetic group

A tightly bound coenzyme that is essential for enzyme activity.

Holoenzyme

he complete, active enzyme formed when an apoenzyme binds its cofactor.

Zymogen

An inactive enzyme precursor that is activated by proteolytic cleavage.

EC classification

Enzyme Commission system that classifies enzymes into six major classes with four-digit codes.

Oxidoreductases

enzymes that catalyze oxidation–reduction reactions.

Transferases

enzymes that transfer functional groups between molecules.

Hydrolases

enzymes that catalyze hydrolysis of bonds

Lyases

enzymes that remove groups to form double bonds without hydrolysis.

Isomerases

enzymes that catalyse isomerization reactions.

Ligases

enzymes that join two substrates with energy from ATP hydrolysis.

Isoenzyme

Different enzyme forms, often tissue-specific, that catalyze the same reaction.

Isoform

Posttranslational variants of an enzyme that differ in properties.

Active site

The region of an enzyme where the substrate binds and the reaction occurs.

Allosteric site

A site other than the active site where regulatory molecules bind to influence enzyme activity.

Induced fit

Model where substrate binding induces a conformational change to tighten the active site.

ES complex

Enzyme–substrate complex; intermediate state that leads to product formation.

Michaelis–Menten equation

v = (Vmax [S])/(Km + [S]); describes reaction velocity vs substrate concentration.

Km Michaelis constant

substrate concentration at which the reaction velocity is half of Vmax; reflects enzyme affinity for substrate.

Vmax

Maximum reaction velocity achieved at saturating substrate concentration.

first-order kinetics

The reaction rate is proportional to the substrate concentration.

Zero Order Kinetics

Reaction rate is independent of substrate concentration when enzyme is saturated.

Substrate concentration

Amount of substrate available for enzyme-catalyzed reaction; influences rate.

Enzyme concentration

Amount of enzyme present; determines the maximum rate under zero-order conditions.

Competitive inhibition

Inhibitor competes with substrate for the active site; Km increases, Vmax unchanged.

Noncompetitive inhibition

Inhibitor binds to enzyme at a site other than the active site; reduces Vmax, Km unchanged.

Uncompetitive inhibition

Inhibitor binds only to the ES complex; lowers both Vmax and Km.

Mixed inhibition

Inhibitor binds to both E and ES with different affinities; alters Vmax and Km variably.

Irreversible inhibitor

inactivator that permanently disables enzyme activity.

International unit (IU)

Amount of enzyme that catalyzes 1 μmol of substrate per minute under defined conditions.

Katal

SI unit of enzyme activity; equal to 1 mole of substrate converted per second.

CK (Creatine kinase)

Enzyme that catalyzes phosphate transfer from ATP to creatine; muscle and heart energy system marker.

CK-MB

Cardiac-specific CK isoenzyme; rises after myocardial injury; useful in AMI diagnosis.

CK-MM

Muscle-type CK isoenzyme; predominant form in skeletal muscle.

CK-BB

Brain-type CK isoenzyme; abundant in brain tissue; less common in plasma.

Lactate dehydrogenase (LD)

enzyme with five isoenzymes (LD-1 to LD-5) used in evaluating tissue damage, especially MI.

AST Aspartate aminotransferase transaminase (SGOT)

elevated in liver and muscle injury; Widely distributed, highest activities in cardiac, liver and skeletal muscle.

ALT

Alanine aminotransferase; liver-enriched transaminase; elevated in hepatic injury.

De Ritis ratio

Ratio of AST to ALT (AST/ALT); helps distinguish hepatic vs. muscle injury.

Alkaline phosphatase (ALP)

nonspecific hydrolase with liver, bone, intestine, and placental isoenzymes.

ALP isoenzymes

Different ALP forms from liver, bone, intestine, and placenta with distinct properties

Acid phosphatase (ACP)

Phosphatase with activity at acidic pH; prostatic ACP is a common clinical target.

Gamma-glutamyltransferase (GGT)

Enzyme indicating hepatobiliary disease; induced by drugs and alcohol; differentiates ALP sources.

5′-Nucleotidase (5NT)

Enzyme associated with hepatobiliary disease; helps differentiate ALP sources.

Amylase (AMY)

Catalyzes the breakdown of starch and glycogen; pancreatic (P-type) and salivary (S-type) isoenzymes; elevated in acute pancreatitis.

Lipase (LPS)

Pancreatic lipase; more specific for pancreatic disease; longer elevation than amylase.

Glucose-6-phosphate dehydrogenase (G6PD)

Enzyme in pentose phosphate pathway; deficiency causes hemolytic anemia; X-linked.

Macroenzymes

High-molecular-weight enzyme forms bound to immunoglobulins or lipoproteins; can cause spurious elevations.

Cytochrome P450 (CYP450)

Family of phase I drug-metabolizing enzymes; genetic variants affect drug metabolism.

NAT2 (N-acetyltransferase 2)

Enzyme with fast/slow acetylator phenotypes; affects isoniazid metabolism and drug reactions.

TPMT (thiopurine methyltransferase)

Enzyme with genetic polymorphisms affecting thiopurine drug metabolism and toxicity risk.

UGT1A1

Enzyme metabolizing bilirubin; variants can cause hyperbilirubinemia.

AST after MI

AST levels begin to rise in 6-8 hours, peak at 24 hours, and return to normal in 5 days

GGT

Used for diagnosis hepatobiliary disorders and chronic alcoholism

Regan ALP

Most heat stable ALP isoenzyme

Bone ALP

Most heat labile in ALP isoenzyme

Placental ALP

Most heat stable among major ALP isoenzyme

ACP

For evaluation of metastatic carcinoma of the prostate

ACP

Enzyme detected in vaginal washing of the rape victim

L-tartrate

inhibits specific prostatic ACP

Osteitis deformans/Paget’s disease

Increased ALP(highest elevation of ALP activity)

GGT

Most sensitive of enzyme assay in all hepatobiliary disorder

GGT

is located in the canaliculi of the hepatic cells and particularly in the epithelial cells lining the biliary ductules