CHEM Serum Enzymes

Question 1

Describe the function and properties of enzymes

Answer 1

• proteins that lower activation energy
• catalyze chemicals reactions without being destroyed/ consumed
• affected by optimal pH and temperatures

Question 2

Differentiate zero vs first-order kinetics

Answer 2

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

Question 3

Compare fixed point vs continuous monitoring (kinetic) methods. Which is preferred ?

Answer 3

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

Question 4

A 10°C increase in temperature doubles the __ of enzyme

Answer 4

A 10°C increase in temperature doubles the REACTION RATE of enzyme

Question 5

Clinical Significance of ALP

Answer 5

• bone development in children (increased levels)
• placental ALP elevated in last trimester of pregnancy
• Hepatobiliary disease, hepatic cancer, hepatitis, cirrhosis

Question 6

Limitations of ALP

Answer 6

• serum or heparin plasma measured within 4 hours
• ALP falsely increases when stored at 4°C and RT
• HEMOLYSIS

Question 7

Clinical Significance of LD

Answer 7

• non-specific indicator of disease
• anemia, liver disease, heart disease

Question 8

Limitations of LD

Answer 8

• serum is preferred: platelets in plasma can increase LD levels
• serum must be stored at RT
• some LD isoenzymes are cold labile
• HEMOLYSIS

Question 9

Clinical Significance of ALT

Answer 9

• hepatic disease

Question 10

Limitations of ALT

Answer 10

• unstable; must be measured within 24 hrs
• stable at -70°C
• HEMOLYSIS; due to endogenous LD enzyme

Question 11

Clinical Significance of GGT

Answer 11

• indicator of 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)

Question 12

Limitations of GGT

Answer 12

• 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)

Question 13

Limitations of CK

Answer 13

• serum and heparin plasma specimens are stable up to 48hrs at 4°C
• HEMOLYSIS; interferes with second hexokinase reaction

Question 14

Clinical Significance of CK

Answer 14

• assessing muscle disease and heart disease

Question 15

Clinical Significance of Amylase

Answer 15

• increased in gland inflammation (mumps virus), and other intra-abdominal disorders (acute pancreatitis*, biliary tract disease, appendicitis, ectopic pregnancy)

*lipase is more specific for acute pancreatitis

Question 16

Limitations of Amylase

Answer 16

• Serum and urine amylase stable at RT
• In vitro, plasma triglycerides inhibit amylase activity
• Morphine and opiates increase amylase

Question 17

Clinical Significance of Lipase

Answer 17

• used to diagnose acute pancreatitis
• also increased in gastric/ duodenal ulcers and intestinal obstruction

Question 18

Limitations of Lipase

Answer 18

• stable in serum at RT for one week
• HEMOLYSIS; hemoglobin inhibits lipase activity
• bilirubin and lipemia interference is method dependent