Re: why is Cu not as effective at catalysing the decomposition of H2o2 than Fe

My mainstay for enzyme data is this database in Germany. You’ll need to register if you haven’t already: http://www.brenda.uni-koeln.de/php/result_flat.php4?ecno=1.11.1.6

Having said that, it wasn’t too useful. This reference is probably worth digging out of your nearest university library:

Diversity of properties among catalases Switala, J.; Loewen, P.C.; Arch. Biochem. Biophys. 401, 145-154 (2002)

Apparently there are many inhibitors compared in this article.

Online data for copper inhibition is sparse. I found two references, one to chard catalase and the other to goat:

Purification and characterization of catalase from chard (Beta vulgaris var. cicla) Dincer, A.; Aydemir, T.; J. Enzyme Inhib. 16, 165-175 (2001) (in this paper, they observed 47% inhibition at 0.2 mM)

and Purification and characterization of catalase from goat (Capra capra) lung Chatterjee, U.; Sanwal, G.G.; Mol. Cell. Biochem. 126, 125-133 (1993) (in which 55% inhibition at 0.2 mM was observed).

If (I think it’s a big if) Cu replaces Fe in a haem (aka heme) ring, it will have two effects.

The reduction potential will change, which will probably make it more difficult for electrons to be transferred between peroxide and the enzyme.

Secondly, the haem may have a role in binding the peroxide, and copper and iron will not have the same binding characteristics. Inhibition could be by copper not binding well, or by the binding being too strong to allow release of product.

Having said that, I’m not sure if copper would swap places with iron in a haem ring and retain its redox activity.

Not a great help, I know!