Subject: Why does the catalase in citrus fruits have a lower optimum acidity level?

For an indivudaul investigation I am investigating the effects of pH change on 
the catalase enzyme, and in particular, comparing the differences in the 
effects, between catalase samples taken from different fruits. As extra 
research I need to back up my hypothesis. So is it the presence of citric acid, 
that makes catalase from citrus fruits work best in more acidic conditions? and 
why is this so?

Re: Why does the catalase in citrus fruits have a lower optimum acidity level?