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MLSCI 262 > 360 - Serum Enzymes > Flashcards

360 - Serum Enzymes Flashcards

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
Q

describe uncompetitive inhibition

A
  • 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.

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26
Q

The concentration of an enzyme in a specimen is _____ proportional to the measurable catalytic activity of the enzyme.

A

directly

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27
Q

how do we measure enzyme activity in the lab?

A

enzyme activity is measured by monitoring a decrease in substrate concentration or an increase in product concentration by spectrophotometry

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28
Q

describe the fixed point method

A
  • 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
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29
Q

describe continuous monitoring kinetic methods

A
  • 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
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30
Q

Why is continuous monitoring preferred to fixed point methodologies?

A

continuous monitoring is preferred to fixed point methodologies because of the shorter reaction time and the ability to verify zero-order kinetics

31
Q

tissue distribution of alkaline phosphatase (ALP)

A
  • high in the intestine, liver, bone, and placenta.
  • on the surface of red blood cells
32
Q

clinical significance of ALP

A
  • 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
Q

ALP levels in different bone diseases

A

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
Q

how does the liver respond to any type of hepatobiliary blockage (ALP)?

A

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
Q

other causes of increased ALP

A
  • 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
Q

Activators for ALP

A

Zn2+, Mg2+

37
Q

Inhibitors or ALP

A

phosphate and anticoagulants: oxalates, citrate, EDTA

38
Q

limitations for ALP reaction

A

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
Q

tissue distribution of lactate dehydrogenase (LD)

A
  • found throughout the body
  • highest concentrations of LD are in the heart, liver, skeletal muscles, red blood cells, platelets & lymph nodes
40
Q

clinical significance of LD

A

LD is a non-specific indicator of disease
There are primarily three clinical uses for LD levels: anemia, liver disease and heart disease

41
Q

LD and anemia

A
  • 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
Q

LD and liver disease

A

LD is increased in viral hepatitis, cirrhosis, and liver cancer
It is not as specific as GGT or ALT for liver diseases

43
Q

LD and heart disease

A

Lactate dehydrogenase is also increased in myocardial infarction but is not as specific as troponins

44
Q

LD reaction coenzyme

A

NAD+

45
Q

LD reaction limitations

A

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
Q

ALT (alanine aminotransferase) tissue distribution

A

ALT is found primarily in the liver and kidneys

47
Q

clinical significance of ALT

A

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
Q

ALT reaction coenzyme

A

pyridoxal 5’ phosphate (vitamin B6)

49
Q

ALT rxn limitations

A

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
Q

GGT (gamma-glutamyl transferase) tissue distribution

A

GGT is expressed in the kidney, the bile ducts of the liver, pancreas and intestine

51
Q

GGT clinical significance

A
  • 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
Q

GGT rxn activator

A

Mg2+

53
Q

GGT rxn inhibitor

A

citrate, oxalate, fluoride

54
Q

GGT rxn limitations

A

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
Q

tissue distribution of creatine kinase (CK)

A

CK is expressed in skeletal muscle, heart, brain

56
Q

clinical significance of CK

A

CK measurements are used in assessing skeletal muscle diseases and heart disease

57
Q

CK and muscle

A

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
Q

CK and heart

A

CK is increased in cardiac disorders, including myocardial infarct; however, cardiac troponins are more specific

59
Q

CK rxn activator

A

Mg 2+

60
Q

CK rxn coenzyme

A

ATP

61
Q

CK inhibitors

A

All anticoagulants other than heparin
Mn2+, Ca2+, Zn2+, Cu2+ and excess Mg2+

62
Q

CK rxn limitations

A

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
Q

tissue distribution of amylase

A

Amylase is found in the salivary glands, pancreas, ovaries, fallopian tubes, and lungs

64
Q

amylase clinical significance

A

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
Q

this enzyme is a more specific enzyme for acute pancreatitis than amylase

A

lipase
Urine and plasma levels should correlate as the kidney freely filters amylase

66
Q

amylase activator

A

Ca2+
absolutely required fo activity

67
Q

amylase rxn inhibitor

A

all anticoags except heparin

68
Q

limitations of amylase rxn

A

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
Q

distribution of lipase AKA triacylglycerol lipase

A

Lipase is found in the pancreas, stomach, and small intestine

70
Q

lipase clinical significance

A
  • 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
Q

methodologies to measure lipase

A

colourimetric, turbidimetric, titrimetric rxns

72
Q

cofactors of lipase

A

colipase and bile salts

73
Q

limitations of lipase

A

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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