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

When (true) catalase is inhibited by copper nitrate, I have been told that the 
copper ion displaces the Fe(III) ion within the heme group of the enzyme. 
Whist the Cu ion can still catalise the reaction, it it not as effective as 
the Fe ion. Why is it not as effective?
Would it be possible to also tell me how Cu is involved in catalysing the 
reaction (I am aware of the basic mechanics of of how Fe is involved when the 
enzyme is not inhibited).
Does the Cu ion bind to the four nitrogen ions in the heme group as Fe does?
Thank you very much for your help, I am very greatfull, as I am finding it 
very difficult to find out information concerning the above.

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