Tag: Isoenzymes

Isoenzymes

ISOENZYMES

Q. 1

True about isoenzymes is:

 A

Same quaternary structure

 B

Same distribution in different organs

 C

Same enzyme classification with same umbers

 D

Catalyze the same reaction

Q. 1

True about isoenzymes is:

 A

Same quaternary structure

 B

Same distribution in different organs

 C

Same enzyme classification with same umbers

 D

Catalyze the same reaction

Ans. D

Explanation:

    • Isoenzymes are the multiple forms of the same enzyme in a single species that catalyze the same chemical reaction or reactions, but differ from each other structurally, electrophoretically and immunologically.
    • Though the same chemical reaction is catalyzed, the different isoenzymes may catalyze the same reaction at different rates.
    • Isoenzymes have different pH optimes, Km and V max values.
    • Isoenzymes may differ in their amino acid sequence and their quarternary structures.
    • The isoenzymes may have different properties also for e.g. LDH-4 and LDH-5 are easily destroyed by heat, whereas LDH-1 and LDH-2 are not, if heated upto 60°C. (Heat resistant).
    • Individual isoenzymes (isozymes) are distinguished and numbered on the basis of electrophoretic mobility, with the number 1 being assigned to that form having the highest mobility toward the anode, for e.g. LDH-1 has the highest mobility towards the anode and LDH-5 is the slowest.
    • Isoenzymes have different tissue distributions. Therefore the pattern of isoenzymes found in the plasma may serve as a means of identifying the site of tissue damage. Example of the diagnostic use of isoenzymes are the study of Lactate Dehydrogenase and Creatine Kinase.

Q. 2

True about isoenzymes is/are:

 A

Different km value

 B

Act on different substrate

 C

Same electrophoretic mobility

 D

All

Q. 2

True about isoenzymes is/are:

 A

Different km value

 B

Act on different substrate

 C

Same electrophoretic mobility

 D

All

Ans. A

Explanation:

  • Isozymes are the physically distinct forms of the same enzymes that catalyze the same reaction, and differ from each other structurally, electrophoretically and immunologically.
  • They differ in their physical properties because of genetically determined difference in amino acid sequence.
  • They are separated by electrophoresis as they have different electrophoretic mobility.
  • They have different Km value.
  • Isoenzyme of an oligomeric enzyme process differ in combination of its peptide protomer.

Q. 3

Which isoenzyme of LDH is seen in heart

 A

LDH 1

 B

LDH 2

 C

LDH 3

 D

LDH 4

Q. 3

Which isoenzyme of LDH is seen in heart

 A

LDH 1

 B

LDH 2

 C

LDH 3

 D

LDH 4

Ans. A

Explanation:

Ans. is ‘a’ i.e., LDH1

Quiz In Between


Q. 4

First enzyme to be raised in MI is ‑

 A

CPK-MB

 B

LDH

 C

Myoglobin

 D

Troponin-I

Q. 4

First enzyme to be raised in MI is ‑

 A

CPK-MB

 B

LDH

 C

Myoglobin

 D

Troponin-I

Ans. C

Explanation:

Ans. is ‘c’ i.e., Myoglobin 


Q. 5

Enzyme specificity is given by ‑

 A

Km

 B

Vrm„

 C

Both

 D

None

Q. 5

Enzyme specificity is given by ‑

 A

Km

 B

Vrm„

 C

Both

 D

None

Ans. A

Explanation:

Ans. is ‘a’ i.e., K. 

  • The Km of an enzyme is the concentration of the substrate that enables the enzyme to function at half maximum activity and is therefore a measure of the specificity of a substrate.for the enzyme” Clinical biochemistry
  • Actually enzyme specificity is not measured by Km alone.
  • It is measured by the ratio Kcat/Km which is a second order rate constant for the reaction between substrate and free enzyme.
  • This ratio is important, for it provides a direct measure of enzyme efficiency and specificity.
  • Note : Kcat is turnover number and measures the rate of the catalytic process.

Q. 6

Q10 in enzyme matches with ‑

 A

2

 B

4

 C

8

 D

10

Q. 6

Q10 in enzyme matches with ‑

 A

2

 B

4

 C

8

 D

10

Ans. A

Explanation:

Ans. is ‘a’ i.e., 2

  • Most enzyme show a 50-300% (average 200%) increase in reaction rate when the temperature is increased by 10°, and the ratio of rate constant at two temperatures 10° apart is usually between 1.5 to 4 (average 2) for most enzymes.
  • This value is termed as Q10.
  • “The rate of enzymatic reaction doubles with every 10° rise in temperature. “

Q. 7

Fastest acting enzyme ‑

 A

LDH

 B

Trypsin

 C

Catalase

 D

None

Q. 7

Fastest acting enzyme ‑

 A

LDH

 B

Trypsin

 C

Catalase

 D

None

Ans. C

Explanation:

Ans. is ‘c’ i.e., Catalase 

Measurement of enzyme activity

  • The activity of enzyme is measured in terms of the following :
  • Unit of enzyme activity : – By international agreement, one unit enzyme activity is defined as the amount causing transformation of 1.0 micro mole of substrate per minute at 25° C. It is usually expressed as mole of substrate disappeared or mole of product formed per minute.
  • Specific activity : – It refers to the number of enzyme units per milligram of protein. It is a measure of enzyme purity; higher the enzyme purity, more is the specific activity.
  • Turn over number : – This refers to the number of substrate molecules transformed per unit time by a single enzyme molecule (or by a single catalytic site), when the enzyme concentration alone is rate-limiting factor. Catalase has the highest turnover number and hence is the fastest active enzyme. Carbonic anydrase has the 2″ fastest turnover number; therefore, it is 2nd fastest active enzyme (after catalase). Lysozyme has the lowest turnover number and therefore is slowest acting.

Quiz In Between



Isoenzymes

ISOENZYMES


ISOENZYMES (ISOZYMES)

  • Isoenzymes are the physically distinct forms of the same enzyme.
  • Isoenzymes differ from each other structurally, electrophoretically and immunologically.
  • Isoenzymes possess quaternary structure and are made up of two or three different subunit (mutimeric).
  • Isoenzymes catalyze the same reaction and act on same substrate, but with different Km and Vmax values i.e. isozymes have different kinetics.

Plasma Enzymes-

  • Functional plasma enzymes- specific function in the plasma. E.g. Coagulation factors (thrombin), lipoprotein lipase, clotting factors.
  • Non functional enzymes- E.g. alkaline phosphatase, acid phosphatase, gamma glutamyl transpeptidase, LDH, Creatine kinase.

Lactate Dehydrogenase (LDH)

  • LDH with two subunits- H(heart) and M(muscle)
  • It has five isoenzymes.
Name of the isoenzyme Tissue location
LDH-1 Heart muscle
LDH-2 RBC
LDH-3 Brain
LDH-4 Liver and skeletal muscle
LDH-5 Liver and skeletal muscle
  • In MI, LDH1 is raised more than LDH2.
  • Normal LDH pattern on electrophoresis is LDH2 > LDHI > LDH 3 > LDH 4>LDH5
  • Increased in LDH level- pancreatitis.

Creatine Kinase (CK)

  • Three isoenzymes.
  • It is subunit M(myocardium) and B (Brain).
Name of isoenzyme Tissue localisation
CK-1 Brain
CK-2 Heart
CK-3 Skeletal Muscle

Alkaline Phosphatase (ALP)-

Isoenzyme Tissue Location
Alpha-1 ALP Epithelial cells of biliary canaculi
Alpha-2 heat liable ALP Hepatic cells
Alpha-2 heat stable ALP Placenta (Inhibited by Phenylalanine)
Pre beta ALP Osteoblast
Gamma ALP Intestinal cells
Leukocyte ALP Leukocytes
  • Raised activity of alkaline phosphatase is useful in diagnosis of bone and liver pathology.

 Transaminase-

  • Aspartate Transaminase- increase in myocardium.
  • Mitochondrial isoenzyme present in liver.
  • Alanine Transaminase (ALT)-  mainly in liver and entirely in Cytoplasm. 

Protease-

  • Serine Proteasesserine residue at the active site(serine, histidine, aspirate).
  • E.g.- Trypsin, chymotrypsin, elastase (catalytic traid)
  • Inhibited by disopropylphosphofluridate binds covalently to serine residue.
  • Activated in intestine by proteolytic activation.

Carboxyl or acid Proteases-

  • Most important carboxyl proteases is Pepsin.

Exam Important

  1. Isoenzymes differ from each other structurally, electrophoretically and immunologically.
  2. Isoenzymes possess quaternary structure and are made up of two or three different subunit (mutimeric).
  3. Functional plasma enzymes- specific function in the plasma.- E.g. Coagulation factors (thrombin), lipoprotein lipase, clotting factors.
  4. Non functional enzymes  E.g. alkaline phosphatase, acid phosphatase, gamma glutamyl transpeptidase, LDH, Creatine kinase.
  5.  LDH has five isoenzymes.
Name of the isoenzyme Tissue location
LDH-1 Heart muscle
LDH-2 RBC
LDH-3 Brain
LDH-4 Liver and skeletal muscle
LDH-5 Liver and skeletal muscle

 6. In MI, LDH1 is raised more than LDH2.

 7. Creatine Kinase (CK)- Three isoenzymes.

CK-1 Brain
CK-2 Heart

 8. ALP found in liver, bone, kidney, intestinal mucosa and placenta.

9. Serine Proteasesserine residue at the active site(serine, histidine, aspirate).

10. Serine proteases- E.g.- Trypsin, chymotrypsin, elastase (Catalytic triad).

11. Serine proteases activated in intestine by proteolytic activation.

12.  Most important carboxyl proteases is Pepsin.

Don’t Forget to Solve all the previous Year Question asked on ISOENZYMES

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