(NOT IN CSMLS?) SERUM ENZYMES Flashcards
Describe the function and properties of enzymes
- proteins that lower activation energy
- catalyze chemicals reactions without being destroyed/ consumed
- there is a relationship between enzyme, substrate, E-S complex, and product
- affected by optimal pH and temperatures
Describe zero and first-order kinetics
Zero Order:
- used in measurement of 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
Fixed Point:
- incubated at a set time and temperature, the reaction is stopped, change in absorbance is measured
- assumes reaction is constant and linear over time and follows zero order kinetics
Continuous Monitoring/ Kinetics:
- incubated at a set time and temperature, and change in absorbance is measured at multiple time points/ continuously until reaction is stopped
- verifies constant linear reaction rate
- 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
Tissue Distribution of ALP
Intestine, liver, bone, placenta, RBC surfaces
- osteoblasts and hepatocytes
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
Diseases from increased ALP
- Bone disease (paget’s disease, hyperparathoidism, osteoporosis)
- Hepatobiliary disease, hepatic cancer, hepatitis, cirrhosis
Activators and Inhibitors of ALP
Activators: Zn2+, Mg2+
Inhibitors: phosphate, anticoagulants (oxalates, citrate, EDTA)
Limitations of ALP
- serum or heparin plasma measured within 4 hours
- ALP falsely increases when stored at 4°C and RT
- HEMOLYSIS
Tissue Distribution of LD
- non-specific; throughout body
- highest in heart, liver, skeletal muscles, RBCs, platelets, lymph nodes
Clinical Significance of LD
- non-specific indicator of disease
- anemia, liver disease, heart disease
Disease of increased LD
- anemia (hemolytic, megaloblastic)
- liver disease (not as specific as GGT or ALT)
- heart disease (not as specific as troponins)
Coenzyme of LD
NAD+
Limitations of LD
- serum is preferred: platelets in plans can increase LD levels
- serum must be stored at RT
- some LD isoenzymes are cold labile
- HEMOLYSIS
ALT Tissue Distribution
- primarily liver and kidneys
Clinical Significance of ALT
- hepatic disease
Coenzyme of ALT
Pyridoxal 5’ phosphate (vitamin B6)
Limitations of ALT
- unstable; must be measured within 24 hrs
- stable at -70°C
- HEMOLYSIS; due to endogenous LD enzyme
Tissue Distribution of GGT
- kidney, bile ducts of liver, pancreas and intestine
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)
Activator and Inhibitors of GGT
Activator: Mg2+
Inhibitor: citrate, oxalate, fluoride
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)
CK Tissue Distribution
- skeletal muscle, heart, brain
Clinical Significance of CK
- assessing muscle disease and heart disease
Diseases of increased CK
- muscle (muscular dystrophy, rnhabdomylosis)
- heart (myocardial infarction, but cardiac troponins are more specific)
Activator, coenzyme, and inhibitors of CK
Activator: Mg2+
Coenzyme: ATP
Inhibitors: all anticoagulants besides heparin (Mn2+, Ca2+, Zn2+, excess Mg2+)
Limitations of CK
- serum and heparin plasma specimens are stable up to 48hrs at 4°C
- HEMOLYSIS; interferes with second hexokinase reaction
Amylase Tissue Distribution
- salivary glands, pancreas, ovaries, fallopian tubes, and lungs
Clinical Significance of Amylase
- 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
Activator and Inhibitors to Amylase
Activator: Ca2+ absolutely required
Inhibitors: all anticoagulants EXCEPT heparin
Limitations of Amylase
- Serum and urine amylase stable at RT
- In vitro, plasma triglycerides inhibit amylase activity
- Morphine and opiates elevate amylase
Lipase Tissue Distribution
- pancreas, stomach, and small intestine
Clinical Significance of Lipase
- used to diagnose acute pancreatitis
- also increased in gastric/ duodenal ulcers and intestinal obstruction
Cofactors of Lipase
- Colipase and bile salts
Limitations of Lipase
- stable in serum at RT for one week
- HEMOLYSIS; hemoglobin inhibits lipase activity
- bilirubin and lipemia interference is method dependent
