lecture 4: Enzymes as catalysts Flashcards
RNAs that act as enzymes called?
Ribozymes
Turnover Number
Substrate to product per second
What enzymes catalyze oxidation-reduction reactions?
Oxidoreductases
What enzymes catalyze transfer of C, N, or P containing groups?
Transferases
What enzyme catalyze cleavage of bonds by addition of water?
Hydrolases
What enzymes catalyze cleavage of CC, CS and CN bonds?
Lyases
What enzymes catalyze rearrangement of bonds
Isomerases
What enzymes catalyze formation of bonds between carbon and O, S, N coupled to hydrolase (glue to other parts of molecule)
Ligases
What are holoenzymes?
complex enzymes with 2 parts: protein component-apoenzyme or cofactor that could be coenzyme or prosthetic group
What is beneficial about compartmentalization of enzymes?
- Isolate
- Provide favorable environment
- Organize into purposeful pathways
Isoenzymes and examples?
Different enzymes that catalyze the same reaction.
Ex. Low Km Hexakinase (High affinity)
High Km Glucokinase (Low affinity)
Proenzymes/zymogens? example?
inactive precursor enzymes, cleaved to activate.
Ex. blood coagulation cascade
Activation-transfer coenzymes vs oxidation-reduction coenzymes
Activation-transfer form covalent bonds with substrate
Oxidation-reduction do not form covalent bonds, donate or accept electrons (NAD, FAD)
What enzyme catalyzes oxidation of ethanol, active site contains Zn2+, requires NAD+ for oxidation
ADH (Alcohol dehydrogenase)
What enzyme converts acetaldehyde (the product of ethanol oxidation, responsible for liver disease from alcoholism) to acetate
ALDH (Acetaldehyde dehydrogenase)
How does alcohol cause fatty liver?
ADH is inhibited by excess NADH, NADH also is not allowed to oxidize fatty acids that will build up in liver.
How does penicillin work as inhibitor?
It forms covalent bond with active site serine of glycopeptidyl transferase, inactivating the enzyme
How does allopurinol work as an inhibitor?
It works as irreversible or “suicide inhibitor” of xanthine oxidase that decreases urate inhibitor and is used in treatment of gout.
How does organophosphorus (nerve gas) work as an inhibitor?
form covalent intermediate with acetylcholinesterase. Meaning that excess acetylcholine is in the cell
How does aspirin work as an inhibitor?
covalently acetylates active site of cyclooxygenase (COX), which is a key enzyme in prostaglandin synthesis
Explain each Heavy Metal Toxicity (Inhibitors) Hg Pb Al Fe
Hg: reacts with selenium required for such selenoenzymes as thioredoxin reductase, which is involved in antioxidant activity.
Pb: is an example of a metal that inhibits by replacing normal functional metal in the enzyme.
Its toxicity may be caused by replacement of Ca2+ in calmodulin and protein kinase C
Al: interferes with iron transport by binding to transferrin and albumin that can cause anemia.
Fe: overload can lead to iron toxicity because high concentration of iron can cause liver failure.
