Your bacterium is growing on a type of medium called casein agar, which contains milk protein (casein). There is a clear zone around the growth area of the bacterium, showing that it is synthesizing the enzymes needed to catalyze the breakdown of casein. These enzymes are considered:
A. apoenzymes.
B. exoenzymes.
C. ribozymes.
D. regulated enzymes.
E. endoenzymes.