|MadSci Network: Biochemistry|
Elle, The activity of most enzymes, not just catalase, differs from one type of tissue to the next. This is not due to any difference in the enzyme itself, but to the fact that different tissues have different amounts of various enzymes. Different organs in our body share many of the same enzymes, but in very different quantities. Different species (such as the apple and potato that you mentioned) frequently share slightly different forms of enzymes that carry out the same catalytic reaction. While these isozymes, as they are called, can differ somewhat in their activity, the biggest difference between the enzymatic activity of a tissue sample from one plant species compared to another is most likely due to differences in the amounts of the enzymes that are present. Similarly, if you examined catalase activity in the fruit compared to the leaves of a particular plant, you would be very likely to find different levels of activity.
Try the links in the MadSci Library for more information on Biochemistry.