enzymes 1 Flashcards
describe the unusual temperature dependence of enzymes
initially, increasing temp will increase rate (2x per 10*C) until temp is too high and enzyme begins to denature, then enzyme activity will decrease
discuss the significance of G6P dehydrogenase mutation
enzyme is impt in RBC membrane, d/t the mutation of G6PD, less NADPH is formed and bc less NADPH is formed, there is less to participate in the reduction of glutathione, leading to less GSH. when GSH levels are low, peroxides and free radicals accumulate, leading to cell damage
which aa form covalent intermediates? (4)
cysteine
lysine
serine
histidine
which aa participate in acid-base catalysis? (2)
histidine
aspartate
which aa stabilize anions? (3)
peptide backbone-NH
arginine-NH
serine-OH
which aa stabilize cations? (1)
aspartate- COO-
function of lyases
add/remove groups to form double bonds
vitamin B1
thyamine pyrophosphate
-aldehyde transfer
- beri-beri if deficient
used by pyruvate dehydrogenase
vitamin B2
riboflavin (FAD)
- Redox
- chellosis, dermatitis
vitamin B6
pyridoxal phosphate
- group transfer to and from aa
- depression, confusion if deficient
used in liver to keep toxic NH2 from accumulating in the blood
nicotinic acid
NAD
- Redox
- pellagra (dermatitis, depression, diarrhea) if deficient
biotin
activates and transfers CO2
coenzyme A
used to transfer acyl groups or thiol esters
cofactor used by alcohol dehydrogenase
NAD
in the active site of alcohol dehydrogenase (3)
Zn, serine and histidine
stereospecificity of alcohol dehydrogenase
enzyme is steroespecific in that H and D forms are not equal
catalysis and motion
enzymes help to catalyze run by restricting motion, the more restricted the motion, the faster the rate of rxn
4 aa found in the active site of all of the serine proteases
serine
histidine
glycine
asparagine
which other enzyme has identical catalytic site to serine proteases?
acetylcholinesterase
MOA of chymotrypsin (9)
- substrate binds to substrate-specificity site
- His activates Ser for nucleophilic attack
- Ser attacks at carbonyl carbon and oxyanion tetrahedral intermediate is formed between Ser, Gly and substrate
- peptide bond is cleaved, amino portion released
- covalent act-intermediate between Ser and substrate
- hydrolysis
- formation of second oxyanion intermediate
- acid-base catalysis with histidine breaks acyl-enzyme bond
- product dissociates
different binding sites for the serine proteases (3)
chymotrypsin- open for large, hydrophobic substrates
trypsin- has aspartate in site (-), so attracts (+) substrate
elastin- has valine and threonine blocking binding site, only allows small substrates like glycine
enzyme that activates trypsinogen –> trypsin
enteropeptidase
3 enzymes activated by trypsin
proelastase –> elastase
procarboxypeptidase –> carboxypeptidase
chymotrypsin –> p-chymotrypsin
what causes the formation of a-chymotrypsin?
p-chymotrypsin (both forms are active)
