CHEM Serum Enzymes Flashcards
Describe the function and properties of enzymes
- proteins that lower activation energy
- catalyze chemicals reactions without being destroyed/ consumed
- affected by optimal pH and temperatures
Differentiate zero vs first-order kinetics
Zero Order:
- measures enzyme activity
- dependent on [enzyme]
- complete saturation of enzymes and EXCESS SUBSTRATE
- reaction velocity Vmax is reached
First Order:
- proportional to [substrate]
- reaction rate reflects the amount of E-S complex formed
Compare fixed point vs continuous monitoring (kinetic) methods. Which is preferred ?
Fixed Point:
- incubated for a set time and temperature = change in absorbance is measured
- assumes reaction is constant, linear over time, and follows zero order kinetics
Continuous Monitoring/ Kinetics:
- incubated at a set time and temperature = change in absorbance is measured AT MULTIPLE POINTS/ CONTINOUSLY until reaction is stopped
- PREFERRED; shorter reaction time and ability to verify zero order kinetics
Differentiate competitive, Non-competitive, and uncompetitive inhibition
Competitive:
- inhibitor is a structural analog of substrate for the active site
- more substrate can be added to reach Vmax to avoid inhibition
- appearance of increased Km when there isn’t
- reversible
Non-Competitive:
- ie. metallic ion binds to allosteric site and causes conformational change
- Vmax cannot be reached
Uncompetitive:
- inhibitor binds to E-S complex and prevents formation of product
- adding more substrate worsens inhibition bc amount of E-S is increased
- decreased Vmax and decreased Km
- reversible
A 10°C increase in temperature doubles the __ of enzyme
A 10°C increase in temperature doubles the REACTION RATE of enzyme
Clinical Significance of ALP
- bone development in children (increased levels)
- placental ALP elevated in last trimester of pregnancy
- Hepatobiliary disease, hepatic cancer, hepatitis, cirrhosis
Limitations of ALP
- serum or heparin plasma measured within 4 hours
- ALP falsely increases when stored at 4°C and RT
- HEMOLYSIS
Clinical Significance of LD
- non-specific indicator of disease
- anemia, liver disease, heart disease
Limitations of LD
- serum is preferred: platelets in plasma can increase LD levels
- serum must be stored at RT
- some LD isoenzymes are cold labile
- HEMOLYSIS
Clinical Significance of ALT
- hepatic disease
Limitations of ALT
- unstable; must be measured within 24 hrs
- stable at -70°C
- HEMOLYSIS; due to endogenous LD enzyme
Clinical Significance of GGT
- indicator if hepatobiliary disease (BILIARY OBSTRUCTION)
- elevated in alcohol use, and liver cancer
- determines whether ALP elevation is due to hepatobiliary disease (increased GGT) or skeletal disease (normal GGT)
Limitations of GGT
- serum and plasma samples are stable at 4°C
- preferably non-hemolyzed
- increased GGT in newborns
- false increase due to drugs (ethanol, warfarin, phenobarbital, phenytoin)
Limitations of CK
- serum and heparin plasma specimens are stable up to 48hrs at 4°C
- HEMOLYSIS; interferes with second hexokinase reaction
Clinical Significance of CK
- assessing muscle disease and heart disease
