|MadSci Network: Biochemistry|
Well, believe it or not from all the searching I have done there seems to be no consensus as to why the heart has such low catalase expression compared to other tissues. Actually, this low level of catalase activity is the reason why the heart is so suseptale to oxidative damage (as mentioned briefly in the 2nd link provided). The research in this area is currently on-going.
Here are some links that provide some of this information:
As for the SOD activity decreasing with age... Well, that is currently another hot topic for which there is no simple answer or consensus. Some of the links below are quite tough reading but the only thing most of these references are able to do is correlate SOD activity with age with little hypotheses as to why this is so. It is most likely the normal process of human development as we age. Some various suggestions are in the links provided below
Some SOD links:
Hopefully, these links will provide a good "jumping-board" for you to search further. But as far as I can tell this research is still being pursued.
Try the links in the MadSci Library for more information on Biochemistry.