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Clinical Chemistry 2 > 9 Enzymes > Flashcards

9 Enzymes Flashcards

1
Q

What are enzymes and where are they found in the body?

A

Enzymes are proteins which act as specific biological catalysts. They increase the rate of chemical reactions in living organisms without themselves being altered.

Enzymes are found in all tissues and fluids, and are responsible for almost every significant life process.

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2
Q

What is the general enzyme reaction?

A

General enzyme reaction:

Enzyme + Substrate → Enzyme/Substrate Complex → Enzyme + Products (E + S → ES → E + P)

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3
Q

What are simple enzymes versus complex enzymes? What is the main difference.

A

Simple enzymes are composed entirely of protein (no cofactors);

Complex enzymes are composed of protein and cofactors, referred to as holoenzymes.

Complex enzymes have cofactors.

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4
Q

What is a apoenzyme?

A

Apoenzyme is the inactive enzyme or protein portion
Cofactor is necessary for enzyme activity or enhances reaction.

Such that –>
Holoenzyme = apoenzyme + cofactor

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5
Q

What is the name of the substance that enhances the enzymes reaction?

A

Cofactor is necessary for enzyme activity or enhances reaction.

Note: Two types of cofactors
1. Activators or inorganic cofactors.
2. Organic cofactors or ‘coenzymes’, often referred to as 2nd substrates. If tightly bound, then called a prosthetic group (non-protein).

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6
Q

What are two types of cofactors?

A
  1. Inorganic cofactor, Activator - such as Mg2+, Cl-, Zn2+, Fe2+, and K+
  2. Organic cofactor can be: Coenzyme - such as NAD, NADP, or FAD. Also referred to as second substrates.
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7
Q

What is a nonprotein which is tightly bound to the apoenzyme called? Name some examples.

A

Prosthetic group - nonprotein which is tightly bound to the apoenzyme such as heme, biotin, flavin, iron sulfides, copper and ubiquinone

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8
Q

What is the coenzyme for Alcohol dehydrogenase to create Acetaldehyde (ethanol) and where does it come from? Give the full reaction.

A

Alcohol dehydrogenase (ADH) holoenzyme with NAD+ acting as a coenzyme

Ethanol + NAD+ Alcohol Dehydrogenase→ Acetaldehyde + NADH + H+ (read at 340 nm)
NAD+ (nicotinamide) is from Vitamin B3 (niacin or nicotinic acid)

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9
Q

What are different names of a structural inactive form of an enzyme called? Give an example used.

A

Proenzyme:
1. Structurally inactive form or enzyme precursor
2. Must be activated. Example: Digestive enzymes
Pepsinogen ↔ Pepsin

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10
Q

What are isoenzymes?

A

Isoenzymes:

  1. Different molecular forms of an enzyme. Similar chemical activity .
  2. Active centers are identical, but different arrangement of amino acids in side chain.

Examples:
Creatine Kinase has 3 isoenzymes
Lactate dehydrogenase or LD or LDH has 5 isoenzymes

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11
Q

What can creatine kinase be used for by Doctors?

A

Creatine Kinase (CK)
Useful for diagnosing and monitoring myopathies or other trauma, toxin or drug-induced muscle injury.

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12
Q

What can increase serum creatine kinase (CK) without it being related to a diagnosis?

A

Exercise can significantly ↑ serum CK activity.

Extent of elevation depends on the severity of exercise and conditioning of the patient.

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13
Q

What are the three different creatine kinase isoenzymes are there subunits? What organs are they related to?

A

Three different creatine kinase isoenzymes composed of two subunits (B= brain; M= muscle)
CK-BB – brain, bowel, prostate
CK-MB – heart and a small amount in skeletal muscle
CK-MM – skeletal muscle and heart

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14
Q

What creatine kinase is related to myocardial infarction and how?

A

CK-MB – heart and a small amount in skeletal muscle

↑ levels with myocardial infarction

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15
Q

What creatine kinase can be related to prostate cancer?

A

CK-BB – brain, bowel, prostate

↑ with cancers in these areas

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16
Q

What creatine kinase is released with tissue damage of skeletal muscle?

A

CK-MM – skeletal muscle and heart

↑ levels with tissue damage

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17
Q

How many isoenzymes does Lactate dehydrogenase make and what are its subunits called? Is this enzyme specific to a condition?

A

Lactate dehydrogenase (LDH) is a tetrameric polymer made of two different types of subunits (H = heart; M = muscle). Different combinations of these subunits is what leads to 5 distinct isoenzymes.

No not specific.
LDH1 & LDH2: Heart and RBC
LDH3 & LDH4: Variety of organs.
LDH5: Skeletal Muscle and Liver

18
Q

What condition is LDH1 elevated in?

A

LDH1: Elevated in Myocardial Infarction

19
Q

What conditions is LDH5 elevated in?

A

LDH5: Elevated in muscle and liver diseases

20
Q

What is IUBMB classification?

A

IUBMB = International Union of Biochemistry and Molecular Biology

Numbering system that divides enzymes into 6 classes:
E.C. = Enzyme Commission
First number = functional class of enzyme
Second and third number = subclasses and sub-subclasses indicating the type of bond attacked
Fourth number = serial number indicating individual enzymes within class

Example: Creatine kinase = E.C.2.7.3.2

21
Q

How are enzymes names most commonly derived?

A

Enzyme Common names: Formed simply by adding “ase” to the substrate name or based on its function.

Example: Urea + ase = Urease
Most commonly used in the laboratory

22
Q

What does the functional class of enzymes called Oxidoreductases do?

A

Oxidoreductases: Catalyze oxidation-reduction reactions (add or remove H+). Often use NAD or NADP.

Example: Lactate Dehydrogenase

23
Q

What is the enzyme category that catalyze the transfer of functional groups between donor and acceptor molecules?

A

Transferases (Functional Class #2)

Example: Aspartate aminotransferase

24
Q

What does Hydrolases do?

A

Catalyze the breaking of bonds through the addition of H2O.

Example: Lipase

25
Q

What is the name of the functional class that the enzyme Carbonic Anhydrase belongs to and what does it do?

A

Lyases: Add or remove H2O, ammonia or CO2 to form or break double bonds.

Functional Class#4

26
Q

What enzymes catalyze the change of one isomer to the other?

A

Isomerases
Functional Class #5

Example: Isomerase

27
Q

What do ligases use to join two chemical groups together?

A

Ligases (Functional Class#6)
Catalyze reactions to join two chemical groups using ATP energy.

Example: Glutamine Synthetase

28
Q

How can enzyme specificity be determined?

A

Enzyme specificity can be determined (demonstrated?) by:

  1. Substrate –> only one substrate catalyzed. E.g. Urease only acts on urea.
  2. Bonds –> Acts only on certain bonds. E.g. Esterase only acts on ester linkages.
  3. Isomer –> Only one isomer of a compound is acted upon. E.g. Glucose oxidase acts on beta-D-glucose only.
  4. Group –> Reacts with a group present in a variety of compounds. E.g. Phosphatases cleave phosphate groups.
29
Q

How do enzymes affect the amount of energy required for the reaction?

A

Most biochemical reactions are NOT spontaneous.

Enzymes are required to reduce the activation energy so products can form.

The enzyme reduces the activation energy but the overall energy released during the reaction is the same (me from graph).

30
Q

What is the Michaelis-Menten Curve?

A

Michaelis-Menten Curve:
Curve that shows the reaction has reached its maximum velocity when all of the specific enzyme has combined with the specific substrate.

At max velocity, further increases in substrate conc. do not increase the rate of the reaction.

31
Q

What is the equation for the rate of reaction (velocity) as per Michaelis-Menten Curve?

A

Michaelis-Menten Curve:
V = Vmax (S) / [Km + S]

Where:
V = rate of reaction or velocity
Vmax = maximum velocity
S = substrate concentration
Km = Michaelis-Menten constant, where substrate concentration at which the reaction velocity is half of the maximum level. Usually expressed as moles/L.
32
Q

How does the affinity of the enzyme relate to the Michaelis-Menten constant if the value is decreased?

A

As Km decreases, the affinity of the enzyme for its substrate increases.

33
Q

What are the characteristics in the region of the Michaelis-Menten Curve referred to as “First-order kinetics” and “Zero-order kinetics”?

A

First Order Kinetics:

  1. Reaction rate is directly proportional to substrate concentration.
  2. Amount of enzyme exceeds substrate.
  3. Measuring quantity of substrate.

Zero Order Kinetics:

  1. Reaction velocity has reached its max.
  2. Substrate is in excess (all enzymes are saturated).
  3. Reaction rate is dependent only on enzyme conc.
  4. Measuring quantity of enzyme.
34
Q

What are the factors affecting enzyme activity?

A
  1. pH: Each enzyme has an optimal pH for max activity. Activity is decreased for pH values lower or higher than the optimal pH. If extreme, could denature enzyme.
  2. Temperature: Activity of enzymes increases with a rise in temp. Protein structure may begin to denature > 40C. Best at 37C.
  3. Substrate Concentration: Enzyme activity is directly proportional to substrate concentration.
  4. Activator Concentration: Rate of reaction depends on the amount of activator present.
  5. Enzyme Concentration: More activity with higher enzyme concentration.
  6. Competitive Inhibitor
  7. Non-competitive Inhibitor
35
Q

What is an inhibitor?

A

An inhibitor is any substance that interferes with the enzymatic reaction.

36
Q

What are they and how do competitive inhibitor versus non-competitive inhibitor affect enzyme reactions?

A

Competitive Inhibitor: Structural similar substrate binds to enzyme at active site and prevents formation of enzyme-substrate complex.

  • Reversible.
  • Decreases or prevents enzyme activity.
  • Can be overcome by increasing amount of substrate present.

Non-competitive Inhibitor - Substance binds at site other than substrate causing shape distortion of the enzyme.

  • Non-reversible
  • Decreases or prevents enzyme activity.
  • CANNOT be overcome by increasing amount of substrate present.
37
Q

How can the lab measure the affect of enzymes?

A

The lab can measure:

  1. Increase in product concentration
  2. Decrease in substrate concentration
  3. Decrease in coenzyme concentration
  4. Increase in concentration of altered coenzyme.
38
Q

How does the lab use enzymes as reagents?

A

The lab can use enzymes as reagents to determine substrate concentration –> add excess quantities of enzyme.

39
Q

What are different types of enzyme assays?

A

Different types of enzyme assays:

  1. One-Point Assay (Fixed Time) - measurement at a fixed time.
  2. End-Point Assays (Fixed Time) - measurement at the end of the reaction.
  3. Multi-Point Assays (Continuous-monitoring) - Measurement at multiple times throughout reaction. Useful when the amount of enzyme is too low to measure.
40
Q

What is the clinical significance of measurement of the lipase & amylase enzyme?

A

Pancreatitis.

Measurement of enzymes aids in diagnosis of disease, follow the course of the disease, or used to monitor treatment.

41
Q

What is the clinical significance of creatine kinase?

A

Creatine Kinase
Myocardial Infarction and Skeletal Muscle Disorders

(although can be increased in all kinds of situations).

Study slide 21 for more common enzymes & clinical significance.

Clinical Chemistry 2 (13 decks)

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