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Clinical Chemistry > Enzymes: Lactate Dehydrogenase and Creatine Kinase > Flashcards

Enzymes: Lactate Dehydrogenase and Creatine Kinase Flashcards

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1
Q

What reaction does Lactate Dehydrogenase catalyze?

A

The oxidation of lactate to pyruvate or pyruvate to lactate

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2
Q

How many pH optimums does the Lactate Dehydrogenase reaction have?

A

2

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3
Q

What is the pH optimum for the forward LD reaction?

A

8.3-8.9

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4
Q

What is the pH optimum for the reverse LD reaction?

A

7.1-7.4

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5
Q

What is the required co-factor for the LD reaction?

A

NAD+

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6
Q

The LD reaction can occur in both directions, which direction does this reaction favor?

A

Reverse (pyruvate to lactate)

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7
Q

Is lactate dehydrogenase specific for lactate and pyruvate?

A

Not absolute specificity. Can also reduce a number of alpha ketoacids and oxidize several alpha hydroxyacids

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8
Q

What is the molecular structure of lactate dehydrogenase?

A

Tetramer (4 polypeptide chains) bound together by disulphide bonds

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9
Q

What are the 2 possible LD subunit types?

A

H and M subtypes

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10
Q

What are some LD inhibitors?

A

Borate, oxalate, EDTA, pyruvate, lactate, reagents with reactivity against thiol groups

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11
Q

How do borate and oxalate inhibit LD enzymatic activity?

A

They compete with lactate for the enzyme binding site

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12
Q

How does EDTA inhibit LD enzymatic activity?

A

It binds with zinc, which acts as an LD activator.

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13
Q

How do pyruvate and lactate inhibit LD enzymatic activity?

A

They inhibit due to excess

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14
Q

Why would serum LD be increased?

A

Heart disease, liver disease, muscle disease, hemolytic disorders, pulmonary disease, cancer

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15
Q

Name H and/or M subunits of LD-1.

A

H4

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16
Q

Name H and/or M subunits of LD-2.

A

H3M

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17
Q

Name H and/or M subunits of LD-3.

A

H2M2

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18
Q

Name H and/or M subunits of LD-4.

A

HM3

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19
Q

Name H and/or M subunits of LD-5.

A

M4

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20
Q

How many LD isoenzymes are there?

A

5 isoenzymes

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21
Q

Which LD isoenzyme(s) will be increased when heart disease is present?

A

LD-1 and LD-2

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22
Q

Which LD isoenzyme(s) will be increased when liver disease is present?

A

LD-4 and LD-5

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23
Q

Which LD isoenzyme(s) will be increased when muscle disease is present?

A

LD-5

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24
Q

Which LD isoenzyme(s) will be increased when hemolytic disorders are present?

A

LD-1 and LD-2

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25
Q

Which LD isoenzyme(s) will be increased when pulmonary disease is present?

A

LD-3

26
Q

Which LD isoenzyme(s) will be increased when cancer is present?

A

LD-4 and LD-5

27
Q

What type of sample is preferred for LD measurement?

A

Serum

28
Q

Why isn’t plasma preferred when LD measurement is done?

A

May be contaminated with platelets, which contain a high concentration of LD

29
Q

Does hemolysis affect LD measurement?

A

Yes, it will falsely elevate the levels due to LD being present in RBCs

30
Q

Which LD isoenzymes are labile to cold?

A

LD-4 and LD-5

31
Q

What is recommended storage for serum used for LD measurement?

A

Keep at room temp because some of the LD isoenzymes are sensitive to cold

32
Q

In children, are LD levels normally higher or lower than adults?

A

5x higher

33
Q

Measurement of LD depends on what?

A

Whether the reaction is occurring in a forward or reverse direction

34
Q

Why is the LD forward reaction the recommended way to measure it?

A

Lactate is more stable than pyruvate as a substrate, less inhibitory

35
Q

What is actually measured when LD enzymatic activity is assayed?

A

As lactate is oxidized to pyruvate, NAD is reduced to NADH. There will be an increase of absorbance at 340 nm.

36
Q

Why would LD isoenzymes be fractionated?

A

To determine the organ of involvement in the disease process

37
Q

Which isoenzyme can be isolated using substrate selectivity with 2-oxybutyrate?

A

LD-1, due to it containing only H subunits, which 2-oxybutyrate has a greater affinity for

38
Q

Immunoprecipitation is used to measure all LD isoenzyme fractions except for?

A

LD-1

39
Q

Which enzyme group does creatine kinase belong to?

A

It is a transferase

40
Q

What reaction does CK catalyze?

A

Catalyzes the reversible transfer of a phosphate group from ATP to creatine

41
Q

What is pH optimum for forward CK activity?

A

9.0

42
Q

What is the pH optimum for reverse CK activity?

A

6.8

43
Q

What ion does CK require to activate the reaction?

A

Mg

44
Q

What compounds can act as inhibitors on CK?

A

(Excess) Mg, Ca, Zn, Cu, sulfhydryl binding reagents, citrate, fluoride, uric acid, excess ADP

45
Q

What is the molecular structure of CK?

A

It is a dimer; 2 peptide chain, B and M joined by disulphide bonds

46
Q

How many CK isoenzymes are there?

A

3 (CK-1, CK-2, CK-3/CK-BB, CK-MB, CK-MM)

47
Q

How is CK relatively unstable?

A

Activity is easily lost when the thiol group in the disulphide bond is broken.

48
Q

Can the disulphide bond in the CK molecule be restored?

A

Partial restoration can occur by adding sulfhydryl compounds

49
Q

What tissue sources is CK-1 (CK-BB) mainly contained in?

A

Brain and nerve tissue

50
Q

What tissue sources is CK-2 (CK-MB) mainly contained in?

A

Heart and skeletal muscle

51
Q

What tissue sources is CK-3 (CK-MM) mainly contained in?

A

Heart and skeletal muscle

52
Q

What are CK isoforms?

A

Subtypes of the CK isoenzymes

53
Q

How are CK isoforms created?

A

Arise from the removal of the terminal lysine on the M peptide chain of the isoenzymes released from the tissues

54
Q

What enzyme catalyzes the removal of the terminal lysine from the M peptide chain on the CK molecule?

A

Carboxypeptidase

55
Q

How many isoforms does CK-3 (CK-MM) have?

A

3

56
Q

Which CK-3 isoform has both lysines intact?

A

MM3

57
Q

Why doesn’t carboxypeptidase have any effect on the CK-1 (CK-BB) isoenzyme?

A

The enzyme only has an effect on the M peptide chain. The CK-1 isoenzyme has only B peptide chain.

58
Q

Which CK-2 (CK-MB) isoform does not have lysine removed?

A

MB2

59
Q

Which CK-2 (CK-MB) isoform has one lysine removed?

A

MB1

60
Q

How long does it take to remove the lysine from the M peptide chains to form the CK isoforms?

A

Takes about 10 hours

61
Q

Which CK-3 isoform has only one of the lysines removed?

A

MM2

62
Q

Which CK-3 isoform has both lysines removed?

A

MM1

Clinical Chemistry (6 decks)

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