Re: In the guiacol-peroxidase reaction, is guaiacol an actual substrate ?

Hi Sara,

I think that some of the confusion on this issue stems from the fact that catalase enzymes are a distinct subset of peroxidase enzymes. As you will see in the link I cited above, the difference between these two types of enzymes is that catalase produces water and O2, while peroxidase produces water and an activated substrate, in your case this activated substrate is tetra-guaiacol.

Guaiacol (also known as 2-methoxyphenol) is a "natural" (I say natural because it was first isolated from Guaiac resin) peroxidase substrate that some plants produce in response to oxidative damage. It serves as a reducing substrate in the reduction of hydrogen peroxide, and is oxidized by the heme co-factor of peroxidases. However, there are a number of other molecules that can serve as peroxidase substrates (e.g., tetramethylbenzidine, caffeic acid, and chlorogenic acid). So, guaiacol really is a substrate of peroxidase. Perhaps it would be best to describe it as a co- substrate, along with hydrogen peroxide.

You can find quite a lot of information about peroxidase in our archives, and here is a primary reference that may be of use to you (assuming that you can find it).

Maehly, A.C. & Chance, B. (1954) The assay of catalases and peroxidases. In Methods of Biochemical Analysis (Glick, D., ed.), Vol. 1, pp. 357-408. Interscience, New York.