Deck 16: Protein Isoforms: Isoenzymes and Isoforms

Question 1

The method of isoenzyme analysis where antibody reacts specifically with one subunit to render that isoenzyme catalytically inactive or remove the isoenzyme altogether is known as:

A)immunoassay technique
B)substrate specificity technique
C)catalytic inhibition
D)immunoinhibition

Answer 1

immunoinhibition

Question 2

What is the limitation of LD isoenzyme measurement in diagnostic enzymology?

A)Since LD catalyzes a reversible reaction, it is difficult to get a true measurement of LD activity.
B)Since LD is found in virtually every tissue, the clinical usefulness in pinpointing areas of disease is extremely limited.
C)LD is found primarily in cells and tissue, making its measurement difficult.
D)all of the above

Answer 2

Since LD is found in virtually every tissue, the clinical usefulness in pinpointing areas of disease is extremely limited.

Question 3

What is the order of electrophoretic migration of the CK-MM isoforms?

A)CK-MM₃, CK-MM₂, CK-MM₁
B)CK-MM₂, CK-MM₁, CK-MM₃
C)CK-MM₂, CK-MM₃, CK-MM₁
D)CK-MM₁, CK-MM₂, CK-MM₃

Answer 3

CK-MM₃, CK-MM₂, CK-MM₁

Question 4

Which of the following statements is true regarding posttranslational modification of alkaline phosphatase (ALP) isoenzymes?

A)ALP isoforms result from the cleavage of terminal amino acids, creating variations in electrical charge and allowing separation by electrophoresis.
B)ALP isoforms result from the addition of carbohydrate side chains, which do not significantly modify electrical charge, making separation by electrophoresis difficult.
C)ALP isoforms result from dephosphorylation reactions that significantly alter the charge of the isoforms, allowing separation by electrophoresis.
D)ALP isoforms result from the addition of lipoprotein side chains, which do not significantly modify electrical charge, making separation by electrophoresis difficult.

Question 5

What is the basic difference between isoenzymes and isoforms?

A)Isoenzymes originate at the gene level, and isoforms originate from the posttranslational modification of the enzyme.
B)Isoforms originate at the gene level, and isoenzymes originate from the posttranslational modification of the enzyme.
C)Isoenzymes are homodimers, and isoforms are heterodimers.
D)Isoenzymes are heteropolymers, and isoforms are homopolymers.

Question 6

All of the following statements are true about the LD₁ isoenzyme except:

A)LD₁ preferably catalyzes the conversion of lactate to pyruvate.
B)LD₁ predominates in tissues that receive a high oxygen supply.
C)LD₁ is found in high concentration in postpubertal testes.
D)LD₁ is found in high concentration in cardiac muscle and erythrocytes.

Question 7

Which of the following describes the key concept for the heat-stability technique of isoenzyme analysis?

A)All enzyme (such as ALP isoenzymes and isoforms) is rendered inactive at the appropriate temperature, allowing pre- and post-measurements to determine enzyme activity.
B)Individual isoenzymes are rendered inactive at different temperatures to allow specific analysis of other isoenzymes.
C)Increasing temperature will increase isoenzyme activity and improve detection up to the point where there is a loss of enzyme stability.
D)Individual isoenzymes are converted to their corresponding isoforms at different temperatures, while other isoenzymes remain unmodified.

Question 8

All of the following statements are true about the LD₅ isoenzyme except:

A)LD₅ has approximately a 10-fold greater affinity for pyruvate than does LD1.
B)LD₅ is a tetramer that consists of four H subunits.
C)LD₅ predominates in tissues that are primarily anaerobic.
D)LD₅ is found in high concentration in skeletal muscle and liver.

Question 9

The CK-MB isoenzyme is typically associated with cardiac muscle.In a situation where there is cardiac muscle damage, what is the approximate maximum level that can be attained by CK-MB?

A)approximately 95% of the total CK activity
B)approximately 70% of the total CK activity
C)approximately 40% of the total CK activity
D)approximately 33% of the total CK activity

Question 10

Which of the following correctly explains why the CK₁ isoenzyme is typically not detected?

A)The molecular weight of CK₁ prevents its passage across the blood-brain barrier, thus it does not appear in the blood stream.
B)CK₁ is not very chromophoric, making it difficult to detect its presence.
C)CK₁ is completely destroyed by plasma enzymes as soon as it enters the blood stream.
D)CK₁ is a neutral molecule and cannot be analyzed by electrophoresis.

Question 11

Which of the following characteristics of isoenzymes result in the difference in catalytic activity seen between different isoenzymes?

A)the organ location of the different isoenzymes
B)the prosthetic group attached to the different isoenzymes
C)the amino-acid sequence difference between isoenzymes
D)all of the above

Question 12

Isoenzymes of an enzyme can differ in which of the following ways?
1)heat stability
2)amino acid composition
3)Michaelis-Menten constants
4)isoelectric points

A)1, 2, 3, 4
B)1, 3, 4
C)1, 2, 3
D)2, 3, 4

Question 13

With which tissue are each of the CK isoenzymes most frequently associated?

A)brain, cardiac muscle, skeletal muscle
B)cardiac muscle, skeletal muscle, brain
C)skeletal muscle, cardiac muscle, brain
D)skeletal muscle, brain, cardiac muscle

Question 14

CK-MM isoforms result from the action of ______ cleaving terminal ______ amino acid residues.

A)aminopeptidase, histidine
B)aminopeptidase, lysine
C)carboxypeptidase, histidine
D)carboxypeptidase, lysine

Question 15

Normal protein degradation by posttranslational modification serves which of the following functions in vivo?

A)to eliminate abnormal proteins that could become harmful at high concentrations
B)to remove enzymes that appear outside their normal cellular location
C)to permit the regulation of cellular metabolism by eliminating superfluous isoenzymes
D)all of the above

Question 16

The most common enzyme group associated with posttranslational proteolytic cleavage of enzymes is:

A)oxidoreductases
B)peptidases
C)transferases
D)isomerases

Question 17

Posttranslational modification of proteins will have the greatest impact on which method of protein analysis?

A)fluorometric analysis
B)turbidimetric analysis
C)immunoassay
D)spectrophotometric analysis