Clinical applications of plasmatic enzymes studies.



Measuring plasma enzymes activity is an important tool in diagnosis and monitoring of treatment.


Enzymes that have a physiological rol in blood, like coagulation enzymes, are present in plasma, but also can be found small quantities of enzymes that normally are present in tissues.


These quantities increase in some diseases of tissues and organs, since as a consequence of increased death cells or changes in cell membranes permeability, intracellular enzymes are released into plasma, giving clues about some organs diseases.


There is a strong association between the finding of an increase in plasma of particular enzymes, and the damage of organs that are rich in those enzymes.


A brief (and incomplete)  list of enzymes that have been useful as diagnostic tools, and its main diagnostic uses include:


Enzymes and Related Diseases


Acid Phosphatase .- Some Prostatic diseases

Alanine aminotransferase (ALT). -Liver, Heart diseases

Aldolase .- Some muscle diseases

Alkaline Phosphatase.- Liver and Bone diseases

Amylase.- Pancreatic diseases

Angiotensin-Converting Enzyme (ACE) .- Active Sarcoidosis

Aspartate aminotransferase (AST).- Heart, Liver diseases

Cholinestarase (pseudocholinestarase).- Acute organophosphorus poisoning

Creatin Kinase (CK or CPK) .- Heart, Muscle diseases

Gamma-Glutamyltransferase (GGT).- Liver disease, alcohol rehabilitation

Lactate Dehydrogenase (LDH).- Heart, Liver, Brain diseases

Lipase .-Pancreatitis

Lysozyme.- Some acute leukemias


More general information about the use of enzymes in diagnostic can be found here.


As discussed previously, some enzymes that catalyze the same reaction, have different structure. They are called Isoenzymes or Isozymes.  The diagnostic importance of  the determination of the different isoenzymes of an enzyme, has been discussed in a former post.


Classify this enzyme


(Question E-15) The enzyme that catalyzes this type of reaction belongs to this class of enzymes:


a)     Class 1: Oxidoreductases


b)     Class 2: Transferases


c)      Class 3: Hydrolases


d)     Class 4: Lyases


e)     Class 5: Isomerases


f)       Class 6: Ligases



Some questions about coenzymes, the organic cofactors of enzymes


(E-12) FMN and FAD have in common that in both structures we can find:


a)     riboflavin

b)     adenosine

c)      AMP

d)     Ribose

e)     Adenine


(E-13) FMN, FAD, NAD+ and NADP+ are organic cofactors in reactions catalyzed by enzymes:


a)     oxidoreductases

b)     lyases

c)      ligases

d)     isomerases

e)     hydrolases

f)       transferases


(E-14) A compound present in NAD+ and NADP+ but not in FMN and FAD is:


a)     Niacin

b)     Riboflavin

c)      Adenin

d)     Ribose

e)     Phosphate


Q: About the regulation of the enzyme activity


(E-11) Which kind of process is represented in the diagram that appears below, considering that:


          increasing the concentration of the Substrate S the activity of the enzyme increases.


          The compound I is not related to the metabolic pathway in which this enzyme participates


          Vmax is not affected by the compound I


          Km increases as result of the presence of I






a)      allosteric activation


b)      allosteric inhibition


c)      competitive inhibition


d)     homotropic interaction


e)      heterotropic interaction


f)       irreversible inhibition


g)      feed back inhibition


h)      feed back activation


i)        non competitive inhibition


Q: About Michaellis Constant (Km)

Enzyme Question No.10 (E-10)



The measuring of the Km in an isomerase that catalyzes the transformation of different D-carbohydrates in the corresponding L- isomers,  show different values, depending on the carbohydrate that is transformed. Given the following carbohydrates  with the corresponding values of Km, mark the one for which the enzyme show less affinity:


a) D-glucose                    Km =  2000 uM


b) D-galactose                Km =   4500 uM


c) D-mannose                Km =  8000 uM


d) D-Ribose                    Km = 10000 uM


e) D-fructose                   Km =  9000 uM


Q: About Enzyme Regulation

Enzyme Question (E-09)


A Protein Kinase

A Protein Kinase







Protein kinases are enzymes that act on other enzymes by adding phosphates groups. When the enzyme is phosphorylated, it changes its activity (it becomes more or less active, depending on the enzyme). This regulatory mechanism of enzymatic activity is called:


a)     Allosteric Control


b)     Competitive inhibition


c)      Covalent Modification


d)     Isozymes Modification


e)     Zymogen activation


Extended Match Question about Enzymes

Read the following options:


a)     absolute specificity over substrate

b)     cooperativity

c)      enzyme activity Unit

d)     heterotropic interaction

e)     homotropic interaction

f)       relative specificity over substrate

g)     specificity of action



Which of them correspond to the definitions described below?


(E-06 ) The fact that an enzyme only catalyzes one of the possible transformations of a substrate:




(E-07 ) The activity that catalyzes the transformation of 1 micromol/minute of substrate:




(E-08 ) The effect of one ligand on an allosteric enzyme, that produces a modification on the binding of a different ligand: