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.

Some basic (biochemistry) comments about H1N1 virus.

 

 

This picture represents an Influenza virus.

 

Observe the capside and the core, containing nucleic acids associated to proteins.

 

The genome of the Influenza A virus is formed by 8 segments of negative sense RNA. Negative sense means that the molecule runs from 3’ to 5’, so it can not be translated to proteins. This type of virus needs a RNA polymerase for the transcription of the original viral RNA to RNA with positive sense (5’3’) that can function as mRNA.

 

Observe also in the viral surface two important glycoproteins: Haemagglutinin and Neuraminidase (Sialidase).

 

Hemagglutinin is a kind of lectin. Lectins are glycoproteins related to cellular recognition. Hemagglutinin in viral capside allows the virus to bind, in lungs and throat, with sialic acid residues (derived of neuraminic acid) that are part of the proteins in the epithelial cell surface. An endocytosis process allows the transport of the virus inside the cell and the eventual replication of the virus.

 

Once the viruses have been replicated inside the cell, they are excreted from the host cell inside a spherical phospholipid membrane that contains Hemagglutinin and Neuraminidase.  In the same say that happened at the beginning of the infection, the Hemagglutinin binds to sialic acid residues, but the Neuraminidase hydrolyses the glycoside linkage between Hemagglutinin and the Sialic Acid residues.

 

N-Acetyl-Neuraminic Acid (Sialic acid)

 

General Action of a Glycosidase (Neuraminidase is a Glycosidase)

 

In the absence of the viral Neuraminidase, the new formed viruses would remain linked to the sialic acids residues in the cell surface or in the glycoproteins in the respiratory tract mucus, and they would get trapped and impeded of infecting other cells. 

 

Hemagglutinin (H) and Neuraminidase (N) also show antigenic properties and Influenza A viruses are classified in subtypes according to the kind of antibodies that these proteins raise. Sixteen subtypes of H (HA) and nine types of N (NA) are known. The Influenza virus H1N1 is then the Influenza A virus with Hemagglutinin subtype H1 and Neuraminidase subtype N1.

 

This picture, from the Influenza Laboratory of the CDC shows the Influenza A H1N1 virus.  (Compare the picture with the graphic shown at the beginning of this post).

 

 

The drugs Oseltamivir (Tamiflu®) and Zanamivir (Relenza ®) have been effective in the treatment of infections with H1N1 virus. These antiviral drugs are potent competitive inhibitors of Neuraminidase, particularly when they are used in the first 48 hours after illness onset, e.g., before the virus is able to release itself from the initial host cells and infect other cells.

 

Updated CDC recommendations about the use of these antiviral agents can be found in these links:

 

 http://www.cdc.gov/h1n1flu/antiviral.htm

 

http://www.cdc.gov/h1n1flu/recommendations.htm

 

This graphic represent the structure of Oseltamivir

 

 

In fact, Oseltamivir is a prodrug (a precursor of the active drug), since the  carboxylic ester linkage is hydrolyzed in the liver, so Oseltamivir becomes  Oseltamivir carboxylate, the active form, with a conformation that looks like the natural substrate of the enzyme, the N-acetyl-neuraminic acid, a form of Sialic acid)

 

 

Updated information about Influenza A H1N1 virus, can be found at the CDC site

 

CDC: H1N1 Flu (Swine Flu)

 

This is the official site of the Mexican government with news and recommendations about the Influenza (in Spanish):

 

http://portal.salud.gob.mx/contenidos/noticias/influenza/profesionales_salud.html

Induced fit model of Enzyme-Substrate interaction

 

Answer to Question E-05

 

b) Induced fit

 

 

The Induced fit model describes the formation of the E-S as a result of the interaction between the  substrate and a flexible active site.  The substrate produces changes in the conformation on the enzyme, aligning properly the groups in the enzyme. It allows  better binding and catalytic effects. 

 

 

 

 

This model opposes to the former Lock and Key model (c) , that explained the formation of the E-S complex as a result of the binding of complementary geometrical rigid structures, as a lock and a key.

 

Follow this link to find a very good animation that represents these two models:

 

http://www.wiley.com/legacy/college/boyer/0470003790/animations/enzyme_binding/enzyme_binding.htm

 

 

The Concerted model (a) and the Sequential model (e) are models used to explain the allosteric changes of conformation of an enzyme from the T structure to the R structure and viceversa. In the concerted model all the subunits that form the allosteric protein change conformation at once, while in the sequential model the change in conformation of one subunit favors the change in conformation of the other subunits and so on.

 

The Michaellis Menten model (d) is related to the kinetics of enzyme catalyzed reactions, and describes the relationship between the concentration of substrate and enzyme velocity in a reaction where no allosteric effects exist.

 

More information about:

 

Michaelis Menten model:

http://themedicalbiochemistrypage.org/enzyme-kinetics.html#michaelis

 

http://en.wikipedia.org/wiki/Michaelis-Menten_kinetics

 

Induced fit model:

http://themedicalbiochemistrypage.org/enzyme-kinetics.html#interactions

 

Concerted Model and Sequential Model:

http://www.aw-bc.com/mathews/ch07/c07hsob.htm

 

http://en.wikipedia.org/wiki/Allosteric_regulation

 

http://www-ssrl.slac.stanford.edu/research/highlights_archive/allosteric_transition.html