Lecture 3 -Enzymes Flashcards
Oxioreductases
Oxidation-reduction reactions
Transferases
Transfer of C, N, or P containing groups
Hydrolases
Cleavage of bonds by addition of water
Isomerases
Racemization of optical or geometric isomers
Ligases
Formation of bonds between carbon and O, S, N coupled to hydrolysis of high energy phosphates
Lyases
Cleavage of C-C, C-O, and C-S and certain C-N bonds
Isoenzymes
Different enzymes that catalyze same reaction, usually in different tissues
-hexokinase/glucokinase -lactate dehydrogenase -creatine kinase
Proenzyme/Zymogen
Inactive enzymes w extra protein sequence activated by cleavage of of protein synthesis
-Digestive proteases -Blood coagulation enzymes
Apoenzyme
Inactive form of enzyme
Holoenzyme
Active form, enzyme + cofactor
Cofactor Types
Metal ions: -Bind substrate or participate in oxidation-reduction
-Small orgnic molecules (coenzyme): -Transfer of chemical groups or oxidation-reduction (usually enzymes)
Vmax
- Theoretical maximum velocity
- Directionally proportional w enzyme concentration
- 1/Vmax is Y intercept on linearized Michaelis-Menten equation (small y-intercept = large Vmax)
Km
- Substrate concentration that permits reaction velocity of Vmax/2
- Inversely related to affinity of enzyme for substrate (high Km=low affinity, low Km = high affinity
- 1/Km is X-intercept on linearized plot (small x intecept = large Km = low affinity)
Product Inhibition
Product of enzymatic reaction is an inhibitor of the enzyme, regulates own synthesis
-Heme
Allosteric Regulation
Regulators bind outside of active site and cause conformational change that alter enzyme activity positively or negatively
-Can change Vmax or Km
Homotropic Effector
- Substrate itself is allosteric effector in multisubunit enzyme
- Binding of substrate to one subunit changes binding of substrate to other units (ex. Binding of O2 to hemoglobin increases affinity)
- Changes shape of curve
Heterotropic Effector
- Allosteric effector is different from substrate
- Doesnt compete for active site (Ex. 2,3-BPG decreases O2 affinity, but doesnt bind active site)
- Changes Km
Phospohorylation/dephosphorylation
Kinases/phosphotases add/remove phosphate groups to enzymes -Changes enzymatic activity depending on enzyme
-Ex. Gycogen synthase phosphorylated is inhibited, glycogen phosphorylase phosphorylated is activated
Proteolytic Processing
-Enzymes are produced in proenzyme (inactive) form -Cleavage of proenzyme leaves active form
Regulation of Enzyme Levels
- Transcription, translation, degredation of enzyme are regulated
- Heme
Negative Feedback Inhibition
End product of pathway regulates first step in pathway
Reversible Enzyme Inhibitors
Bind non-covalently to enzyme, so can be dissociated from enzyme
- Competitive
- Noncompetetive
Competetive
Inhibitor competes with the substrate at the active site
Drugs: -Statins -Ibuprofen -Catopril
Non Competetive
Inhibitor does NOT compete w enzyme at active site
Irreversible Enzyme Inhibitors
Bind very tightly (usually covalently) to active site and prevent substrate binding
- Transition-state (Active site-directed)
- Suicide Inhibitors (Enzyme-activated)
Transition-state (Active site-directed)
Inhibitor (without alteration in its structure) forms covalent linkage w catalytic site
Drugs: -Organophosphates -Aspirin
Suicide Inhibitors (Enzyme-activated)
Enzyme modifies inhibitor, inhibitor binds very tightly to active site and cant be displaced
Drugs: -Penicillin -Allopurinol
AST
-Aspartate Aminotransferase
-Aspartate -> glutamate
Tissue: heart, skeletal muscle, liver, brain
Diagnostic Use: liver disease
ALT
-Alanine Aminotransferase
-Alanine -> glutamate
Tissue:Liver
Diagnostic Use: Liver disease (ALT> AST)
Amylase
Tissue: Pancreas, Salivary gland
Diagnostic Use: Acute pancreatitis, biliary obstruction
CK
-Creatine Kinase
Tissue: Skeletal muscle, heart, brain
Diagnostic Use: Muscular dystrophy, MI
GGT
Tissue: Liver
Diagnostic Use: hepatitis, cirrhosis
LDH
Tissue: Heart, liver erythrocytes
Diagnostic Use: Lymphoma, hepatitis
Lipase
Tissue: Pancreas
Diagnostic Use: Acute pancreatitis, biliary obstruction
Alkaline Phosphatase
Tissue: Osteoblast
Diagnostic Use: bone disease/tumors
Acid Phosphatase
Tissue: Prostate
Diagnostic Use: Prostate cancer
