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MLSCI 262 > 360 - Serum Enzymes > Flashcards

360 - Serum Enzymes Flashcards

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1
Q

the amount of energy needed to raise all the molecules in 1 mol of a compound at a certain temperature to the transitional state at the peak of the energy barrier

A

activation energy
- this corresponds to the formation of an activated enzyme-substrate complex

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2
Q

group of enzymes that catalyze the same reaction but are encoded by different genes

A

isoenzymes
- each has different molecular structure and varying physical, immunological, and biochemical properties

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3
Q

non-protein molecules needed for enzyme activity.

A

cofactor
ex: activators, coenzymes

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4
Q

inorganic cofactor, that when bound to an enzyme increases the enzyme’s activity

A

activator
ex: Cl-, Mg2+

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5
Q

organic, low molecular weight, substances which combines with an inactive protein

A

coenzyme

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6
Q

what is a holoenzyme?

A

a coenzyme and apoenzyme forms holoenzyme or a complete enzyme

the active form of an apoenzyme formed by the combination of the apoenzyme with its coenzyme (prosthetic group), e.g. alanine transferase and pyridoxal phosphate

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7
Q

T or F. Coenzymes are more complex than activators, e.g. NAD+ and NADP+, vitamins

A

T!

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8
Q

an inactive form of an enzyme that requires a coenzyme to be converted into an active holoenzyme

A

apoenzyme

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9
Q

what is a prosthetic group?

A

a coenzyme bound to an apoenzyme, e.g. pyridoxal phosphate bound to an apoenzyme

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10
Q

denaturation

A
  • change in the structure of a protein accompanied by a loss of activity
  • can be caused by extreme pH, elevated temperature, changes in ionic strength and chemical modifiers
  • can be reversible or irreversible.
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11
Q

how do enzymes work?

A

proteins that function as catalysts by lowering the activation energy
they are not consumed or destroyed in the process

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12
Q

Most physiological enzymes perform optimally in the pH range

A

7.0 to 8.0
Shifts in pH can change the ionization of enzymes active site or the substrate and can cause conformational changes in the structure of the enzyme

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13
Q

Effect of extreme pH shifts

A

it can irreversibly denature an enzyme

buffers control the pH of enzyme rxns

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14
Q

Most physiological enzymes have optimal activity at this temperature

A

37C
- As temperature increases interactions between enzymes and substrates become more common
- 10°C increase in temperature doubles the reaction rate
- temperature rises too high = enzyme is inactivated and irreversibly denatured

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15
Q

The rate of the enzymatic reaction is dependent on the concentration of enzyme

A

zero order kinetics

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16
Q

Describe zero order kinetics

A
  • dependent on enzyme concentration
  • occurs at high substrate concentration
  • complete saturation of enzyme by excess substrate
  • rxn reaches Vmax
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17
Q

rate reaction is directly proportional to the concentration of the substrate

A

first order kinetics

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18
Q

describe first order kinetics

A
  • velocity of the enzymatic reaction will increase as more substrate is added until Vmax is reached
  • as the amount of substrate decreases, the reaction rate decreases
  • reaction rate reflects the amount of enzyme-substrate complex formed
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19
Q

describe competitive inhibition

A

inhibitor = structural analog of substrate and competes w the substrate for the active site of the enzyme
- rxn can reach same Vmax, just slower
- enzyme Km is constant bc more substrate required to overcome inhibition; there is appearance of increased Km
- reverisble

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20
Q

T or F. Competitive inhibition can be overcome by adding more substrate

A

T! This is so that the substrate concentration is greater than the inhibitor

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21
Q

when an inhibitor, often a metallic ion, binds to the enzyme at an allosteric site causing conformational changes in the enzyme structure

A

non-competitive inhibition
- not reversible

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22
Q

T or F. In non-competitive inhibition, the inhibitor does not alter the affinity of the enzyme for the substrate

A

T!
- The substrate concentration does not modify the interaction between the inhibitor and the enzyme, therefore increasing the substrate concentration will not overcome inhibition, and thus Km is unaltered

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23
Q

T or F. In non-competitive inhibition, Vmax is reached

A

F! binding of the inhibitor to the enzyme slows down the reaction rate, and Vmax cannot be reached

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24
Q

when the inhibitor binds to the enzyme-substrate complex preventing the creation of the product

A

uncompetitive inhibition

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25
describe uncompetitive inhibition
- adding more substrate increases the amount of enzyme-substrate complex, which worsening the inhibition and free enzyme concentration is reduced = decreased Vmax and decreased in Km. reversible.
26
The concentration of an enzyme in a specimen is _____ proportional to the measurable catalytic activity of the enzyme.
directly
27
how do we measure enzyme activity in the lab?
enzyme activity is measured by monitoring a decrease in substrate concentration or an increase in product concentration by spectrophotometry
28
describe the fixed point method
- started, incubated for a specified time at a set temperature - reaction is stopped, and the change in absorbance is measured - run over a few seconds to a few minutes - assumed the reaction is constant and linear over time and follows zero-order kinetics
29
describe continuous monitoring kinetic methods
- started, incubated at a set temperature for a set time - change in absorbance (or amount of product formed) is measured at multiple time points or continuously until the reaction is stopped **multiple readings verifies a constant linear reaction rate**
30
Why is continuous monitoring preferred to fixed point methodologies?
continuous monitoring is preferred to fixed point methodologies because of the shorter reaction time and the ability to verify zero-order kinetics
31
tissue distribution of alkaline phosphatase (ALP)
- high in the intestine, liver, bone, and placenta. - on the surface of red blood cells
32
clinical significance of ALP
- osteoblasts and hepatocytes - active bone growth, children = higher levels of ALP than adults - placental forms of ALP, enter the circulation and result in elevated plasma ALP concentrations during the last trimester of pregnancy
33
ALP levels in different bone diseases
Paget’s disease, 10 - 25X the normal upper limit Osteomalacia, rickets, 2 - 4X the normal upper limit Hyperparathyroidism (slight to mod increase) In osteoporosis, levels are usually normal or slightly increased
34
how does the liver respond to any type of hepatobiliary blockage (ALP)?
produce more ALP 3-10X normal upper limit - similar can be seen in hepatic cancer; 10-20X normal upper limit - liver diseases such as hepatitis and cirrhosis that affect the parenchymal cells may demonstrate a slight rise in ALP
35
other causes of increased ALP
- individuals undergoing hemodialysis - individuals with cancer (due to presence of variant carcinoplacental forms of ALP - Regan + Nagoa) - these forms of ALP similar to placental form and can cause increased ALP concentrations
36
Activators for ALP
Zn2+, Mg2+
37
Inhibitors or ALP
phosphate and anticoagulants: oxalates, citrate, EDTA
38
limitations for ALP reaction
Serum or heparin plasma should be measured within 4 hours ALP increases on storage at 4°C and room temperature DO NOT USE HEMOLYZED SPECIMENS Bilirubin and lipemia are not causes of significant interference
39
tissue distribution of lactate dehydrogenase (LD)
- found throughout the body - highest concentrations of LD are in the heart, liver, skeletal muscles, red blood cells, platelets & lymph nodes
40
clinical significance of LD
LD is a non-specific indicator of disease There are primarily three clinical uses for LD levels: anemia, liver disease and heart disease
41
LD and anemia
- an increase in serum LD is observed in hemolytic anemias and megaloblastic anemias - LD is also useful for predictive monitoring in leukemia and lymphoma
42
LD and liver disease
LD is increased in viral hepatitis, cirrhosis, and liver cancer It is not as specific as GGT or ALT for liver diseases
43
LD and heart disease
Lactate dehydrogenase is also increased in myocardial infarction but is not as specific as troponins
44
LD reaction coenzyme
NAD+
45
LD reaction limitations
serum sample is preferred; platelets in plasma can increase LD levels Store serum samples at room temperature Some LD isoenzymes are cold labile DO NOT USE HEMOLYZED SPECIMENS Bilirubin and lipemia are not causes of significant interference
46
ALT (alanine aminotransferase) tissue distribution
ALT is found primarily in the liver and kidneys
47
clinical significance of ALT
ALT is increased in hepatic diseases In viral hepatitis and acute hepatic, necrosis ALT can increase 10 - 40X the normal upper limit Acetaminophen toxicity ALT >85X the normal upper limit Elevated concentrations of ALT may also be observed in non-alcoholic fatty liver disease, metabolic syndrome
48
ALT reaction coenzyme
pyridoxal 5' phosphate (vitamin B6)
49
ALT rxn limitations
ALT is unstable and should be measured on the same day ALT is stable at -70°C Hemolysis may falsely elevate results due to the release of endogenous LD enzyme Bilirubin and lipemia are not causes of significant interference
50
GGT (gamma-glutamyl transferase) tissue distribution
GGT is expressed in the kidney, the bile ducts of the liver, pancreas and intestine
51
GGT clinical significance
- an indicator of hepatobiliary disease, especially biliary obstruction - elevated in alcoholic hepatitis, heavy alcohol drinkers and liver cancer - can help in determining whether observed ALP elevations are due to hepatobiliary disease (cholestasis) or skeletal disease as GGT is normal in skeletal disorders and pregnancy
52
GGT rxn activator
Mg2+
53
GGT rxn inhibitor
citrate, oxalate, fluoride
54
GGT rxn limitations
Serum and plasma samples are stable at 4°C A non-hemolyzed sample is preferred Bilirubin and lipemia are not causes of significant interference GGT levels are higher levels in newborns The following drugs can cause a false increase up to 4X the normal upper limit: ethanol, warfarin, phenobarbital, and phenytoin
55
tissue distribution of creatine kinase (CK)
CK is expressed in skeletal muscle, heart, brain
56
clinical significance of CK
CK measurements are used in assessing skeletal muscle diseases and heart disease
57
CK and muscle
CK is increased in all forms of muscular dystrophy CK is increased in viral and polymyositis, rhabdomyolysis, and muscle trauma It is NOT increased in neurogenic diseases, e.g. multiple sclerosis, Parkinsonism
58
CK and heart
CK is increased in cardiac disorders, including myocardial infarct; however, cardiac troponins are more specific
59
CK rxn activator
Mg 2+
60
CK rxn coenzyme
ATP
61
CK inhibitors
All anticoagulants other than heparin Mn2+, Ca2+, Zn2+, Cu2+ and excess Mg2+
62
CK rxn limitations
Serum and heparin plasma specimens are stable for up to 48h at 4°C Gross hemolysis will interfere with the second hexokinase reaction due to the presence of enzymes and reaction intermediates Bilirubin and lipemia do not significantly interfere
63
tissue distribution of amylase
Amylase is found in the salivary glands, pancreas, ovaries, fallopian tubes, and lungs
64
amylase clinical significance
Amylase activity is increased in salivary gland inflammation, e.g. mumps virus Amylase activity is increased in acute pancreatitis and other intra-abdominal disorders, e.g. biliary tract disease, intestinal obstruction, appendicitis, and ectopic pregnancy
65
this enzyme is a more specific enzyme for acute pancreatitis than amylase
lipase Urine and plasma levels should correlate as the kidney freely filters amylase
66
amylase activator
Ca2+ absolutely required fo activity
67
amylase rxn inhibitor
all anticoags except heparin
68
limitations of amylase rxn
Serum and urine amylase is stable at room temperature In vitro, plasma triglycerides inhibit amylase activity Morphine and opiates elevate amylase Hemolysis, bilirubin, and lipemia do not cause significant interference
69
distribution of lipase AKA triacylglycerol lipase
Lipase is found in the pancreas, stomach, and small intestine
70
lipase clinical significance
- used to diagnose acute pancreatitis > In acute pancreatitis, serum lipase rises 4-8 hours after onset of symptoms, peaks at 24h, and diminishes to normal within 7-14 days - Lipase >3X the normal upper limit is indicative of acute pancreatitis - also increased in gastric or duodenal ulcers and intestinal obstruction
71
methodologies to measure lipase
colourimetric, turbidimetric, titrimetric rxns
72
cofactors of lipase
colipase and bile salts
73
limitations of lipase
Lipase is stable in serum at RT for one week Hemolysis should be avoided as hemoglobin inhibits lipase activity Bilirubin and lipemia interference is method dependent

MLSCI 262 (21 decks)

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