Re: What might affect metabolism and hence catalase production in vertebrates?

Daniel:

You have several questions here, I will answer them in the order you asked.

1) What is Catalase?

Catalase is an enzyme.  That means it is a protein that catalyzes some 
reaction or conversion and is not consumed in the process.  In this case 
(See #3) it is responsible for degrading hydrogen peroxide into water and 
oxygen.  When we say it is a protein, we mean that it is a chain of amino 
acids that assumes some shape (or fold) in 3-dimensions which makes it 
catalase and not amylase, (which is another enzyme found in saliva).


2) Where is it produced and found in vertebrates?

In vertebrates, it is produced or present in virtually every cell in the 
body.  Peroxide is a common by-product of many metabolic reactions, and is 
toxic to cells, so it must be degraded quickly.  Most of the catalase is 
contained within organelles inside cells that contain a large collection 
of different oxygen-reacting enzymes.  this bag of enzymes, if you will is 
called the peroxisome.  Catalase, specifically, is made like all proteins, 
which is from a gene that is transcribed into an mRNA template, which 
directs the ribosome on the correct sequence and order of amino acids to 
assemble to form the correct protein.  Like most proteins that react with 
oxygen, catalase contains a Heme molecule, just like hemoglobin, to help 
it hold onto oxygens as the chemistry of reducing hydrogen peroxide occurs.

3) Where is it found in the liver?

In the liver, like all cells, catalase is primarily contained inside the 
peroxisomes.  There is a lot of catalse concentrated in the liver, because 
in vertebrates, this is where most metabolic and anabolic processes occur 
for the entire body, and thus most of the peroxide is generated there, so 
it needs more catalase to react with it as it is produced.
  
4) What is its purpose genrally and specifically in
relation to (Hydrogen or other) Peroxide?

Its purpose is solely to catayze the reduction of 2H2O2 into two molecules 
of water and one molecule of molecular oxygen O2.  Catalase is not 
effective at converting other reactive oxygen species inside of 
organisms.  Peroxi radicals, superoxide, nitric oxide and others are 
reduced and eliminated by other enzymes, many of which are found in the 
peroxisome as well, such as super oxide dismutase.
     Catalase is actually thought to be a 'perfect' enzyme.  That is 
essentially every time a molecule of peroxide collides with it, the 
chemistry occurs, and there is no limiting step to this process such as 
binding, or accidental release, or that the formation of product (Oxygen 
and water) is much much faster than the reverse reaction back to 
substrate.  (Remember, all chemical reactions catalyzed by enzymes can go 
backwards as well).  In the case of catalase, the only limiting step to 
the rate of chemistry is how quickly you can feed peroxide to it, which we 
define as the limit of diffusion.


5) Since catalase is involved in metabolism, What
differences are there between different vertebrates
(e.g. between say birds and mammals and fish) that
might affect metabolism and therefore catalase
production in that type of vertebrate?

You are absolutely correct to say that catalse is involved in metabolism.  
But since it is such a fast enzyme, it is not a very good stage at which 
to try and reguate metabolism, particularly since the substrate it 
eliminates is toxic.  It is possible that birds, which have very high 
rates of oxidative metabolism produce more catalase than mammals, but 
virtually any catalase, even from horseradishes is already 'perfect' and 
would be difficult to determine differences between them.  If we look at 
the sequence of the DNA in plants versus fungus versus humans for 
catalase, they are actually quite similar as well, implying that catalase
(s) are all decended from a common ancestral protein.  For example, Cow 
catalase is almost identical to the catalse found in Bakers Yeast, and 
human catalse is almost exactly the same as that found in dogs, mice, 
worms, frogs, zebrafish, slime molds and wheat, and that is just a few.

I hope this helps you in your research on catalase.  Thanks

-Matt-

Sources:
Voet and Voet Biochemistry 2nd Edition
NCBI Blast searches
SWISS-PROT www.expasy.ch