7: Enzyme kinetics and Creatine Kinase Flashcards
Vmax
maximum speed the reaction can go
-levels out when saturated
Kmax
Point of half of Vmax
How much substrate will make an enzyme work half as fast
Low Kmax
strong binding of enzyme to substrate
High Kmax
weak binding of enzyme to substrate
Competitive inhibitors
structurally similar to substrate
competes with substrate to bind at active site
increasing substrate can overcome inhibition
Kmax increases, Vmax doesn’t
non-competitive inhibitors
structurally different from substrate
bind to enzymes on allosteric site
Increasing substrate does not overcome inhibition
Vmax decreases, Km remains the same
Creatine Kinase is
an enzyme present in most tissues at relatively low levels
present at higher levels in the brain, heart, skeletal muscle as they have higher metabolic activity
Creatine kinase catalyses
ATP <—> creatine phosphate + ADP
Creatine kinase is used by cells as
an energy buffer
Creatine kinase structure
dimeric protein
2 genes code for 2 different monomers
M and B
What creatine kinase monomers do skeletal muscles produce
MM only
What creatine kinase monomers does the brain produce
BB only
What creatine kinase monomer does the heart muscle produce
only cell transcribing both genes, mainly produces MB but also some MM and BB
What happens when cells are damaged to creatine kinase levels
CK is release into the bloodstream, its activity can be measured using a coupled assay
Cardiac Troponin I is a
Highly specific and sensitive marker For myocardial injury
Commonly used to diagnose myocardial infarction
Aspartate transaminase (AST)
Can be elevated in setting of myocardial infarction
Not specific and used less frequently
Alkaline Phosphate (ALP)
Not typically used as a bio marker for myocardial infarction
More commonly used with liver and bone disease diagnosis
Lactate dehydrogenase (LDH)
Can be elevated following myocardial damage
Less specific and less commonly used
Creatine kinase - MB
(CK-MB)
Used to assess cardiac damage
Especially useful for diagnosing myocardial infarction
Although cardiac troponins more specific
How long after a myocardial infarction, do cardiac Troponin I and T levels remain elevated in serum?
5 days
The exact duration of elevation may vary depending on factors such as the extent of myocardial damage and individual patient characteristics.
In a Lineweaver-Burk plot the slope, Y intercept and X intercept can be calculated different equations. What are the characteristics of this graph
Slope=Km/Vmax, Y intercept = 1/Vmax, X intercept = -1/Km
Michaelins constant
conc. of substrate at which enzyme works at half its max velocity
KM = -1/intercept
Which type of peptide bond does chymotrypsin specifically cleave?
Bonds between bulky hydrophobic side chains
- due to presence of hydrophobic pocket in chymotrypsin active site which accommodates bulky hydrophobic amino acid residues such as phenylalanine, tryptophan and tyrosine
Following a severe Myocardial infarction, a patients blood test shows significantly elevated levels of a certain creatine kinase isoenzyme.
MB
- cardiac-specific isoenzyme
- typically rise within hours of MI, peak at 24-48h
return to normal within 48-72h
