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Michelle: Clinical Chem > Week 3: Enzymes > Flashcards

Week 3: Enzymes Flashcards

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1
Q

T/F: Enzymes alter both biochem rxn AND chem equilibrium point of rxn

A

FALSE

Alter rate of biochcem rxn but not chem equilibrium point

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2
Q

Why is the measurement of enzymes clinically relevant?

A

Enzyme concentration can be measured to detect cellular injury or altered production by specific organ tissue

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3
Q

What is the general enzyme rxn equation?

A

E + S -> E*S -> E + P

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4
Q

Define adduct

A

Enzyme-substrate complex

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5
Q

What is a catalyst?

A

Same as enzyme! Accelerates rate of reaction without being modified itself

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6
Q

Define cofactor and give examples

A

Definition: Non-protein, molecules essential for enzyme activity and must bind enzyme to alter configuration for optimum substrate binding

Examples: Mg2+, Cl-, Zn- (activators)

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7
Q

Define coenzyme and give examples

A

Definition: Organic molecules that loosely bind proteins and are required for enzyme function. Participate in rxn but are not substrates. Carry electrons, atoms, or functional groups

Example: NADH

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8
Q

Apoenzyme

A

protein portion of enzyme

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9
Q

Holoenzyme

A

enzyme + coenzyme

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10
Q

Zymogen

A

Inactive, secreted form of enzyme

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11
Q

Prosthetic group

A

Tightly bound non-protein molecules of organic OR non-organic (metal ion) origin

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12
Q

What type of bond is present in the adduct?

A

Noncovalent bonds

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13
Q

What are general enzyme reaction conditions?

A
  • Usually 37°C, no higher than 40°C
  • -5°C are inactivated and stored
  • Most pH ranges are 7-8
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14
Q

First-order kinetics

A

Constant [E] with increasing [S] and increasing reaction rate

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15
Q

Zero-order kinetics

A

All enzyme sites are saturated with substrate. Constant reaction rate that depends on [E]

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16
Q

Post-zone phenomenon

A

Antigen excess (substrate excess)

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17
Q

Prozone phenomenon

A

Antibody excess (enzyme excess)

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18
Q

Hook effect

A

Decrease in signal due to excess analyte concentration (outside of analytical range). See data increase and then “hook” down

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19
Q

Enzyme reaction conditions when measuring reaction rate

A
  • [S] > [E]
  • Change in [product] must solely depend on [E]
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20
Q

Km

A

[S] which is half of Vmax

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21
Q

Difference between non-competitive and uncompetitive inhibitors?

A

Non-competitive: Allosteric inhibitor binds enzyme and may allow substrate binding but can’t form product

Uncompetitive: Inhibitor binds enzyme-substrate complex and prevents product formation

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22
Q

As long as [S] > [E], enzyme velocity is proportional to ___

A

[E]

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23
Q

List clinically significant enzymes

A
  • Lactate dehydrogenase (LD)
  • Creatine kinase (CK)
  • Aspartate amino transferase (AST)
  • Alanine amino transferase (ALT)
  • Gamma glutamyl transferase (GGT)
  • Alkaline phosphatase (ALP)
  • Amylase (AMY)
  • Lipase (LIP)
  • Cholinesterase/pseudocholinesterase
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24
Q

Purpose of aminotransferase (aka transaminase?

A

To transfer amino groups for the formation of oxaloacetate and pyruvate

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25
List the two aminotransferases and their end products
AST = oxaloacetate ALT = pyruvate
26
What can increase liver enzyme activity?
Inflamed liver tissue, infection
27
Describe **AST** (aspartate aminotransferase)
- In liver, heart, skeletal muscle, and kidney tissue - Cytoplasm + mitochondria - Short half-life increases clinician value - Normal: [AST] < [ALT]
28
In which diseases is [AST] > [ALT]?
- Alcoholic hepatitis - Hepatic cirrhosis - Hepatocellular carcinoma
29
Why should you avoid hemolysis when measuring AST?
False increase in [AST]
30
Describe **ALT** (alanine aminotransferase)
- Primarily in liver + kidney tissue - **Greater specificity for damaged liver than AST** - Cytoplasm
31
ALT is the best predictor of liver damage associated with which conditions?
- Viral hepatitis - hepatic cirrhosis due to non-alcoholic, fatty liver disease - Hepatitis caused by drug abuse (e.g., fentanyl causes massive increase in AST and ALT)
32
How do you measure AST and ALT (aminotransferase assay)?
- Form oxaloacetate and oxidize NADH - Measure decrease in absorbance at 340 nm 3 times
33
Describe alkaline phosphatase (ALP)
- Catalyzes hydrolysis at **alkaline** pH - Membranes of small intestines, kidneys, liver, bone, and placenta - Clinical lab only analyzes liver ALP isoenzyme - Liver isoenzyme > bone isoenzyme > intestinal placenta isoenzyme - Magnesium activator
34
List disease states associated with ALP
- Obstructive hepatobiliary disease - Osteoblast-mediated bone disease
35
Describe ALP assay
- No NADH used - 4-NPP converts to 4-NP (yellow) - Measure increase in absorbance at 405 nm three times
36
List interfering factors in ALP assay
- Hemolysis causes false increase since intracellular ALP gets released - Chelating anticoags (e.g., citrate, oxalate, EDTA) should not be used bc can interfere with Zn and Mg cofactors - If liver disease not implicated (regular ALT + AST), then order ALP isoenzyme panel to find tissue of origin
37
Describe acid phosphatase
- optimal pH < 7 (acidic) - Prostate, bone, liver, spleen, kidney, RBCs, plts - **Aids detection of prostatic carcinoma, especially metastatic**
38
Describe Gamma-glutamyl transferase (GGT)
- Found in kidney, liver, pancreas, and intestines - Cell membrane and cytoplasm - Involved in glutathione metabolism + membrane transport of aa + peptides
39
Disease states associated with GGT?
- Mostly hepatobiliary disorders - Metastatic carcinoma (super high GGT) - Severe alcoholism + drug use - Normal during pregnancy + bone disorder pts
40
Which enzyme should be measured to screen for alcohol use and why?
GGT because it takes longer to return to normal levels after drinking
41
Which wavelength is used for the GGT assay?
Measure at 410 nm
42
Describe acinar cells in pancreas
- Create bicarb-heavy alkaline fluid to neutralize stomach acid in intestines - Get inflamed with super fatty foods
43
Describe amylase
- **Functions** to break down carbs into simple sugars - S-amylase secreted by salivary glands to start sugar digestion - P-amylase secreted by pancreatic acinar cells to further sugar breakdown - Good indicator of pancreatic injury **but not best diagnostic test for pancreatitis** - High concentration gradient between plasma and acinar cells - Amylase is small enough to be excreted through urine
44
Disease states associated with high **plasma** amylase levels
- Acute/chronic pancreatitis - Hereditary pancreatitis - Pancreatic carcinoma
45
Describe amylase levels in populations that eat high carb vs high protein diets
High carb = higher amylase levels High protein = lower amylase levels
46
What is the time frame of detectable amylase activity in acute pancreatitis pts?
- 5-8 hours after symptom onset - Activity peaks after 12-48 hrs - Return to normal 3-4 days post-symptom onset
47
List interfering factors in amylase assay
- Calcium-chelating anticoags (EDTA, citrate, oxalate) inhibit amylase - Only use heparinized plasma, tho most often assayed on **serum** - Add 24-hr urine amylase test to serum amylase test bc not specific to acute pancreatitis
48
Describe lipase
- **Functions** to hydrolyze triglycerides to glycerol - **Only test needed to diagnose acute pancreatitis** - Lipase level just above ref range considered to "reach threshold" for diagnosis - Usually low levels in normal ppl
49
Disease states associated with abnormal lipase levels
- Acute pancreatitis (super specific) - Chronic pancreatitis - Celiac disease - Crohn's disease - Cystic fibrosis - Pancreatic carcinoma
50
Lipase enzyme is almost exclusive to which organ?
**Pancreas** [pancrea lipase] up to 5000x higher than in other tissues
51
Lipase assay methods
- Old = turbidemetry to measure fatty acid release - New = synthetic substrates in one coupled-enzyme, continuous monitoring method
52
Describe creatine kinase (CK)
- Uses ATP to convert creatine to creatine phosphate (energy source for muscles) - Fwd rxn occurs in mitochondria - Found primarily in cardiac + musculoskeletal tissue - In cytoplasm, CK also phosphorylates ADP to ATP for muscle contraction (rvs rxn)
53
Where are the following CK isoenzymes found: - CK-MB - CK- MM - CK-BB
- CK-MB = cardiac tissue - CK-MM = muscle tissue - CK-BB = brain tissue
54
Disease states associated with high CK levels
- Muscular dystrophy - Acute rhabdomyolysis - **Acute myocardial infarction (most common disease associated with high CK)** - Severe fall - Trauma - Surgery
55
Interfering factors with CK measurement?
- CK is unstable, so quickly store after analysis - Hemolysis falsely increases [CK] - Coupled-enzyme test only measures **total** CK, so order specific immunoassay test or perform protein electrophoresis to ID isoenzyme
56
Describe lactate dehydrogenase (LADH)
- **Functions** to moderate interconversion between lactate and pyruvic acids
57
Disease states associated with **moderate** increase of LADH?
- Acute myocardial infarction (AMI) - Pulmonary embolism - Leukemia - Hemolytic anemia - Liver and renal diseases
58
Disease states associated with **severe** increase of LADH?
- Pernicious anemia - Megaloblastic anemia - Cancer
59
LADH assay limitations?
- Old assay - General disease marker, not specific - 5 isoenzymes exist
60
Order of LADH isoenzyme concentrations in normal patients?
LD2 > LD1 > LD3 > LD4 > LD5
61
Order of LADH isoenzyme concentration in AMI pt?
LD1 > LD2 > LD3 > LD4 > LD5
62
Describe LADH assay
Labs measure lactic acid conversion to pyruvic acid and measure formation of NADH (increase in absorbance, NAD+ gets reduced)

Michelle: Clinical Chem (4 decks)

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