Enzymes: properties and physiology (LD, CK, ALT, AST, ALP, GGT, amylase, lipase)

17 ASCP MLS practice questions on Enzymes: properties and physiology (LD, CK, ALT, AST, ALP, GGT, amylase, lipase), part of Chemistry. The first 17 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Hard
A 27-year-old man has a raised ALP on an insurance screen drawn about 90 minutes after a large fried lunch. Results: ALP 162 U/L (reference 40-130), GGT 22 U/L (below 50), ALT 24 U/L and AST 21 U/L (both below 40), total bilirubin 0.6 mg/dL [10 µmol/L], calcium 9.5 mg/dL [2.37 mmol/L] (8.6-10.2), phosphate 3.6 mg/dL [1.16 mmol/L] (2.5-4.5), 25-hydroxyvitamin D 34 ng/mL [85 nmol/L]. He is blood group O and a secretor. A repeat ALP after a 12-hour fast is 98 U/L. Which ALP isoenzyme most likely caused the first result?
1. ALiver ALP
2. BPlacental-like (Regan) ALP
3. CBone ALP
4. DIntestinal ALP
Show answerHide answer
Answer: D · Intestinal ALP
Intestinal ALP enters the blood after a fatty meal, especially in people of blood group O or B who are secretors. A normal GGT argues against a liver source, and his age with normal calcium, phosphate and vitamin D argues against bone. The ALP fell back into the reference range after a 12-hour fast, which fits a meal-related rise, whereas bone or tumor-related ALP would stay raised. On electrophoresis, intestinal ALP moves most slowly toward the anode. This is one reason ALP is best measured on a fasting sample.
- A: A normal GGT makes a liver source unlikely.
- B: A tumor-related isoenzyme would not disappear after an overnight fast.
- C: His growth has ended, calcium, phosphate and vitamin D are normal, and bone ALP would not fall after a fast.
Question 2 · Medium
On electrophoresis at pH 8.6, in what order do the CK isoenzymes lie, from the anode toward the cathode?
1. ABB, MB, MM
2. BMB, BB, MM
3. CMM, MB, BB
4. DMB, MM, BB
Show answerHide answer
Answer: A · BB, MB, MM
At pH 8.6 the B subunit carries more negative charge than the M subunit. CK-BB (CK-1) therefore moves fastest toward the anode, CK-MB (CK-2) lies in the middle, and CK-MM (CK-3) stays near the point of application on the cathode side. The isoenzyme numbers follow this order of migration. Unusual bands, such as the macro-CKs, are identified by where they run relative to these three.
- B: CK-BB, not CK-MB, moves fastest toward the anode.
- C: This is the reverse order, from cathode to anode.
- D: CK-MM moves least, so it cannot lie between MB and BB.
Question 3 · Hard
An enzyme has a Km of 2.0 mmol/L for its substrate. At a substrate concentration of 18 mmol/L, the reaction velocity is what percentage of Vmax?
1. A90%
2. B10%
3. C100%
4. D50%
Show answerHide answer
Answer: A · 90%
The Michaelis-Menten equation is v = Vmax × [S] / (Km + [S]). Here v = Vmax × 18 / (2 + 18) = 0.90 × Vmax, or 90%. Velocity approaches Vmax only gradually, so a substrate concentration 9 times the Km still gives 90%, not 100%. This is why enzyme assays set the substrate concentration well above the Km.
- B: 10% is Km / (Km + [S]), the fraction of enzyme left free.
- C: 100% would need an infinitely high substrate concentration.
- D: 50% of Vmax occurs when [S] equals the Km, 2.0 mmol/L.
Question 4 · Easy
Amylase needs which ions for full activity?
1. AMagnesium and zinc
2. BSodium and potassium
3. CCalcium and chloride
4. DMagnesium alone
Show answerHide answer
Answer: C · Calcium and chloride
Amylase is a calcium metalloenzyme, and chloride is its activator. It hydrolyzes α-1,4 glycosidic bonds in starch and glycogen. Because it needs calcium, EDTA, citrate and oxalate inhibit it, so serum or heparin plasma is used. Magnesium activates CK and ALP, and ALP also contains zinc.
- A: Magnesium and zinc are needed by alkaline phosphatase.
- B: Sodium and potassium do not activate amylase.
- D: Magnesium is the activator of CK.
Question 5 · Easy
Alkaline phosphatase belongs to which enzyme class?
1. AOxidoreductases
2. BLyases
3. CTransferases
4. DHydrolases
Show answerHide answer
Answer: D · Hydrolases
Hydrolases split bonds by adding water, and ALP removes phosphate groups from organic esters at an alkaline pH. Amylase and lipase are also hydrolases. Transferases such as AST, ALT, CK and GGT move groups between molecules, and oxidoreductases such as LD catalyze redox reactions. ALP is usually assayed with p-nitrophenyl phosphate, which it hydrolyzes to yellow p-nitrophenol.
- A: Oxidoreductases such as LD transfer electrons.
- B: Lyases such as aldolase split bonds without water or oxidation.
- C: Transferases such as AST, ALT, CK and GGT move groups between molecules.
Question 6 · Hard
A 74-year-old woman with no cardiac symptoms has a persistently raised CK-MB by an immunoinhibition method. CK electrophoresis shows an extra band between CK-MM and CK-MB that is still present months later. The most likely cause is:
1. ACK-MB from a recent infarction
2. BMacro-CK type 2 (mitochondrial CK)
3. CMacro-CK type 1 (CK-BB bound to IgG)
4. DCK-BB released from a brain injury
Answer and explanation in LearnFree account
Question 7 · Medium
When serum is heated at 56 °C for 10 minutes, which ALP isoenzyme loses its activity most readily?
1. APlacental ALP
2. BLiver ALP
3. CIntestinal ALP
4. DBone ALP
Answer and explanation in LearnFree account
Question 8 · Easy
Which LD isoenzyme moves fastest toward the anode and is the main form in heart muscle and red cells?
1. ALD2
2. BLD5
3. CLD1
4. DLD3
Answer and explanation in LearnFree account
Question 9 · Medium
A competitive inhibitor changes enzyme kinetics by:
1. ARaising Km; Vmax unchanged
2. BRaising both Km and Vmax
3. CLowering both Km and Vmax
4. DLowering Vmax; Km unchanged
Answer and explanation in LearnFree account
Question 10 · Medium
Pancreatic lipase acts on triglyceride only at an oil-water interface. For full activity it needs:
1. AChloride ions
2. BPyridoxal 5'-phosphate
3. CColipase and bile salts
4. DMagnesium and zinc ions
Answer and explanation in LearnFree account
Question 11 · Easy
Which CK isoenzyme makes up almost all of the CK in skeletal muscle?
1. ACK-MM
2. BMitochondrial CK
3. CCK-BB
4. DCK-MB
Answer and explanation in LearnFree account
Question 12 · Easy
AST and ALT both require which coenzyme for full activity?
1. AThiamine pyrophosphate
2. BNADH
3. CPyridoxal 5'-phosphate (vitamin B6)
4. DFlavin adenine dinucleotide
Answer and explanation in LearnFree account
Question 13 · Hard
Kinetic studies give these results. Without inhibitor: Km 4.0 mmol/L, Vmax 200 U/L. With inhibitor: Km 2.0 mmol/L, Vmax 100 U/L. Which type of inhibition fits?
1. ANoncompetitive
2. BIrreversible
3. CCompetitive
4. DUncompetitive
Answer and explanation in LearnFree account
Question 14 · Medium
On a Lineweaver-Burk (double reciprocal) plot, the y-intercept equals:
1. A1/Vmax
2. B−1/Km
3. CVmax/2
4. DKm/Vmax
Answer and explanation in LearnFree account
Question 15 · Medium
In macroamylasemia, serum amylase is high but urine amylase is low. Why?
1. APancreatic amylase is released in an inactive form
2. BThe kidney tubules reabsorb more filtered amylase
3. CSalivary-type amylase is not filtered by glomeruli
4. DAmylase bound to immunoglobulin is too large to filter
Answer and explanation in LearnFree account
Question 16 · Easy
An enzyme activity assay should run where the reaction rate depends only on the amount of enzyme. Which region of the Michaelis-Menten curve shown meets this condition?
Figure: MedExams
1. ARegion A
2. BRegion D
3. CRegion B
4. DRegion C
Answer and explanation in LearnFree account
Question 17 · Medium
The double-reciprocal plot shown compares an enzyme with and without inhibitor X. How does X change the kinetic constants?
Figure: MedExams
1. AVmax falls; Km is unchanged
2. BKm and Vmax both fall
3. CKm rises; Vmax is unchanged
4. DVmax rises; Km is unchanged
Answer and explanation in LearnFree account

Enzymes: properties and physiology (LD, CK, ALT, AST, ALP, GGT, amylase, lipase)

On electrophoresis at pH 8.6, in what order do the CK isoenzymes lie, from the anode toward the cathode?

An enzyme has a Km of 2.0 mmol/L for its substrate. At a substrate concentration of 18 mmol/L, the reaction velocity is what percentage of Vmax?

Amylase needs which ions for full activity?

Alkaline phosphatase belongs to which enzyme class?

A 74-year-old woman with no cardiac symptoms has a persistently raised CK-MB by an immunoinhibition method. CK electrophoresis shows an extra band between CK-MM and CK-MB that is still present months later. The most likely cause is:

When serum is heated at 56 °C for 10 minutes, which ALP isoenzyme loses its activity most readily?

Which LD isoenzyme moves fastest toward the anode and is the main form in heart muscle and red cells?

A competitive inhibitor changes enzyme kinetics by:

Pancreatic lipase acts on triglyceride only at an oil-water interface. For full activity it needs:

Which CK isoenzyme makes up almost all of the CK in skeletal muscle?

AST and ALT both require which coenzyme for full activity?

Kinetic studies give these results. Without inhibitor: Km 4.0 mmol/L, Vmax 200 U/L. With inhibitor: Km 2.0 mmol/L, Vmax 100 U/L. Which type of inhibition fits?

On a Lineweaver-Burk (double reciprocal) plot, the y-intercept equals:

In macroamylasemia, serum amylase is high but urine amylase is low. Why?

An enzyme activity assay should run where the reaction rate depends only on the amount of enzyme. Which region of the Michaelis-Menten curve shown meets this condition?

The double-reciprocal plot shown compares an enzyme with and without inhibitor X. How does X change the kinetic constants?