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Clinical Chemistry > Enzymes: Transferases > Flashcards

Enzymes: Transferases Flashcards

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0
Q

Once the alpha-ketoglutarate accepts the amine group, what is it converted to?

A

L-glutamate

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1
Q

What reaction do the aminotransferases catalyze?

A

The transfer of an amine group to an alpha-ketoglutarate.

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2
Q

What varies for each aminotransferase when the amino acid is donated?

A

The amino acid substrate that donates the amine group

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3
Q

What is required to transfer the amine group to alpha-ketoglutarate?

A

Pyridoxal-5-phosphate

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4
Q

What other name is pyridoxal-5-phosphate known as?

A

Vitamin B6

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5
Q

What does AST stand for?

A

Aspartate aminotransferase

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7
Q

What does ALT stand for?

A

Alanine aminotransferase

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8
Q

What is the pH optimum for AST and ALT?

A

7.3-7.8

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9
Q

How long is AST stable when refrigerated?

A

3-4 days

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10
Q

What reaction does AST catalyze?

A

The amine transfer from aspartic acid to alpha-ketoglutarate

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11
Q

What are the products formed when AST catalyzes a reaction?

A

Oxaloacetate and L-glutamate

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12
Q

Does hemolysis affect AST measurement?

A

Yes, it falsely increases AST activity due to AST being present in RBCs.

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13
Q

Where is AST found in highest concentrations?

A

Heart, liver, skeletal muscle

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14
Q

Where is AST found in smaller amounts?

A

Kidney, pancreas, spleen, lung, RBC

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15
Q

In what disease states is an elevated AST seen in?

A

Heart disease, liver disease, skeletal muscle disorders, pulmonary embolism, acute pancreatitis

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16
Q

Is an elevated AST diagnostic for an AMI?

A

No, it has limited diagnostic use due to it taking too long to increase (6-8 hours after pain onset).

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17
Q

In viral hepatitis, how many times the URL will AST be increased?

A

30-50x the URL

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18
Q

In toxic hepatitis, how many times the URL will AST be increased?

A

As high as 100x the URL

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19
Q

What reaction does ALT catalyze?

A

The transfer of an amine group on alanine to alpha-ketoglutarate

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20
Q

What products are formed in the reaction ALT catalyzes?

A

Pyruvate and glutamate

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21
Q

How long is ALT stable at refrigerated temperature?

A

3-4 days

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22
Q

Is ALT measurement affected by hemolysis?

A

No

23
Q

Where is ALT found in highest concentration?

A

Liver

24
Q

Where else can ALT be found in the body?

A

Widely distributed through the body in small amounts (heart, kidney, skeletal muscle)

25
Q

In what disease states is ALT elevated in?

A

Liver disease (viral/toxic hepatitis, cirrhosis, hepatic obstructive disorders)

26
Q

In what disease state will ALT be higher than AST?

A

Acute inflammatory process (like hepatitis)

27
Q

In what disease state will AST be higher than ALT?

A

Severe liver necrosis (cirrhosis and hepatocellular carcinoma)

28
Q

Why is AST higher than ALT in severe liver necrosis?

A

Mitochondrial AST is stored in RBCs and as scar tissue replaces living tissue, AST is released from the RBCs, leading to the elevated levels?

29
Q

What is the difference between ALT and AST measurement?

A

Each utilize a different substrate

30
Q

What are the substrates used for AST measurement?

A

Alpha-ketoglutarate and aspartate

31
Q

What are the substrates used for ALT measurement?

A

Alpha-ketoglutarate and alanine

32
Q

What is the name of the method used to measure ALT and AST?

A

Karmen method

33
Q

What is actually measured in the Karmen method?

A

As NADH is converted to NAD, a decrease in absorbance at 340 nm is observed which is proportional to AST activity

34
Q

In the measurement of AST, what enzyme is used to catalyze the conversion of oxaloacetate to malate?

A

Malate dehydrogenase

35
Q

What does GGT stand for?

A

Gamma-glutamyltransferase

36
Q

What reaction does GGT catalyze?

A

Catalyzes the transfer of a gamma-glutamyl group from a donor peptide to an acceptor compound.

37
Q

What type of molecules can be acceptor of a gamma glutamyl group from a donor peptide?

A

Another peptide, an amino acid, or water

38
Q

Where is GGT found?

A

Found in most cells, in the cell membrane

39
Q

Where is the highest amounts of GGT found in the body?

A

In the kidney

40
Q

Besides, the kidney, where else can GGT be found?

A

Liver, prostate, pancreas and brain

41
Q

GGT found in the serum originates from what body system?

A

Hepatobiliary system

42
Q

What disease is GGT elevations sensitive for?

A

Liver disease

43
Q

Why is GGT the most sensitive out of all the liver enzymes?

A

It elevates first and persists longer

44
Q

GGT levels can help interpret elevated levels of what enzyme?

A

ALP

45
Q

If ALP and GGT are both elevated, what disease does this indicate?

A

Hepatic disease

46
Q

If ALP is elevated and GGT is normal, what does this say about the source of the ALP?

A

Nonhepatic source, like bone disease, pregnancy or childhood bone growth

47
Q

What drugs can induce GGT synthesis and elevate serum levels?

A

Alcohol intake, phenytoin and barbituates

48
Q

What specimen is preferred for GGT analysis?

A

Serum or EDTA plasma

49
Q

Why isn’t heparin preferred for GGT analysis?

A

Heparin causes turbidity in the reaction mixture and thus, interferes with the measurement

50
Q

How long is the sample for GGT analysis stable at refrigerated temperature?

A

7 days

51
Q

How long is the sample used for GGT analysis stable if frozen?

A

2-3 months

52
Q

What is a common substrate used for GGT measurement?

A

Gamma-glutamyl-p-nitroanilide

53
Q

What is produced when GGT reacts with gamma-glutamyl-p-nitroanilide?

A

p-nitroaniline is formed

54
Q

What is measured in GGT analysis?

A

p-nitroaniline, which is yellow

Clinical Chemistry (6 decks)

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