enzyme II: enzyme kinetics Flashcards
what is enzyme kinetics?
The study of the rate of an enzyme controlled reaction (to see the effect of substrate concentration, of different inhibitors/drugs or different isozymes/mutations)
what is The Michaelis-Menten equation?
Vo= Vmax [S] /Km+ [s]
what does Vmax represent ?
Here, Vmax represents the maximum velocity achieved by the system at saturating substrate concentrations.
what does the Km represent ?
Km (the Michaelis constant) is the substrate concentration at which the reaction velocity is 50% of the Vmax.
[S] is the concentration of the substrate S.
what does a high
Vmax and a low Km say about an enzyme ?
A fast, efficient, specific enzyme has a high
Vmax and a low Km
high Vmax allows fastest rate of reaction.
Low Km means fast reaction rate at low concentrationof substrate.
which type Km and Vmax is more responsive to substrate concentration near saturation ?
high Vmax but low Km .
how can you tell the difference between isozymes?
Km often used to distinguish between different forms of the same enzyme (isoenzymes).
how is the Km related to substrate concentration in cells?
Km of an enzyme for a substrate is often near the concentration of that substrate in a cell, allowing enzymes to be more responsive to substrate concentrations
what reaction does hexokinase catylyse
Hexokinase catalyses phosphorylation of glucose to Glucose-6-Phosphate
what inhibits hexokinase?
inhibited allosterically by Glc-6-P
what is the normal glucose conc in the blood stream and in the cell?
Norm blood conc=5mmol/L so in intracellular levels are 0.2-2mmol/L
what is the Vmax and Km of hexokinase?
Heokinase is efficient (50-90% Vmax) under normal conditions
Has a low Km (0.2mmol/L)
where is glucokinase found?
Hepatocytes (store glucose as glycogen) and pancreatic β cells contain glucokinase
whats is the km value of glucokinase ? i it inhibited by anything?
Glucokinase has a Km of 10mmol/L & is not inhibited by Glc-6-P
what is the function of Glucokinase and how is it importent?
Its activity increases after a meal
Results in storage of glucose & release of insulin
Mice lacking the enzyme die within 3days due to sever hyperglycaemia
what occurs to alcohol when consumed
Sensitivity of some people to alcohol
Exhibit facial flushing and tachycardia after small amounts of alcohol
alcohol converts into acetaldehyde by enzyme called Alcohol dehydrogenase.
what enzyme processes acetaldehyde.
The acetaldehyde is processed by aldehyde dehydrogenase
There is two forms of aldehyde dehydrogenase , where are they found
aldehyde dehydrogenase:
a low Km mitochondrial and
a high Km cytoplasmic form
Sensitivity of some people to alcohol is due to a mutation that occurs. what is this mutation and why do they show this symptom.
Due to a mutation some people lack the mitochondrial form od aldehyde dehydrogenase .
High concentrations of acetaldehyde need to build before a high rate of catalysis can occur due to lack of low Km enzyme.
how is Vo measured?
Lineweaver-Burk plot
Vmax is achieved at infinite substrate concentration, so it is impossible to estimate Vmax and Km from a hyperbolic plot
Vo is measured at different [S] then a plot of 1/Vo against 1/[S] is made
