enzymes 2 Flashcards
what is vmax?
enzyme rate when the substrate is saturated
what is Km?
concentration at which v = 1/2 Vmax
hexokinase vs. glucokinase
hexokinase in peripheral tissues, lower Km
glucokinase in liver, higher km
catalyze same rxn
consequence of low vs high km
low km = more activity at lower substrate concentrations
high km= need high substrate concentration for enzyme activity
metabolism of ethanol
ethanol to acetaldehyde by alcohol dehydrogenase
acetaldehyde to acetate by acetaldehyde dehydrogenase
effects of acetaldehyde
toxic, very reactive
consequence of absence of low Km form of acetaldehyde dehydrogenase
mitochondrial form is low Km form, but if this is absent, much use cytosolic form which has high km- this means that there must be a higher substrate concentration for the high Km form to be active and higher concentration of acetaldehyde = more toxic effects, tachycardia and flushing
effect of competitive inhibitors on km? vmax?
km will increase
vmax unchanged
effect of noncompetitive inhibitors on km? vmax?
km unchanged
vmax will decrease - inhibitor stops the enzyme from working properly
effect of organophosphates on AchE active site
organophosphate will form a covalent bond with serine in the active site and prevent AchE from working properly
shape of substrate vs. velocity curve for allosteric enzymes
sigmoidal
effect of an activator on the curve
shift to left, increased activate at lower [S] = lower km
effect of inhibitor on the curve
shifts to right, decreased activity at lower [S] = higher km
R state vs t state
R state= low km, high activity
T state = high km, low activity
enzyme that regulates pyrimidine synthesis in e. coli
aspartate transcarboxylase
activator and inhibitor of aspartate transcarboxylase
activator = ATP
inhibitor = CTP
either can bbd to regulatory site
structure of aspartate transcarboxylase
6 catalytic subunits
6 regulatory subunits
which aa can be phosphorylated? (3)
serine
threonine
tyrosine
what is the effect of phosphorylation?
gives (-) charge, allows for the formation of more H bonds
describe regulation of protein kinase A
cAMP bind to the regulatory subunits, causing them to dissociate from the catalytic subunits, catalytic subunits free to bind substrate
what is the regulatory subunit of PKA an example of?
“pseudo-substrate”
effects of epinephrine on blood sugar
epinephrine increases blood sugar through a cAMP dependent mechanism- PKA will phosphorylate and activate phosphorylase (breaks down glycogen into glucose) AND will phosphorylate and inactivate glycogen synthase (synthesizes glycogen) == increased blood glucose
how does calmodulin active enzymes?
calmodulin-activated kinases are auto inhibited with pseudo-substrate, once activated, calmodulin will bind the pseudo-substrate to release the auto inhibition and free the active site to function as kinase
example of calmodulin dependent kinase
MLCK
