Final answer:
Casease is identified as an exoenzyme because it operates outside of the cell, breaking down the protein casein found in milk. Its activity can be observed externally, in contrast to cytoplasmic enzymes which function within the cell. The extracellular function of casease characterizes it as an extracellular protease.
Step-by-step explanation:
To determine whether casease is an exoenzyme or a cytoplasmic enzyme, we can refer to its function in the context of where it acts upon its substrate. Casease is an enzyme that degrades casein, which is the main protein found in milk. The degradation occurs outside of the microbial cell, as can be seen when microbes are grown on skim milk agar and produce a zone of clearing around their growth due to the action of casease on casein. Thus, since the activity of casease is exerted outside the cell, casease is classified as an extracellular protease.
In contrast, cytoplasmic enzymes, such as cytochrome C, act within a cell. An example of a cytoplasmic enzyme's action is its role in apoptosis, where cytochrome C released from mitochondria in the cell aids in the activation of caspases, leading to cell death.
Casease's role in protein catabolism is essential for microbial digestion of proteins into smaller peptides that can be taken up by the cell. This functional distinction between casease and cytoplasmic enzymes demonstrates why casease is considered an exoenzyme, which is produced inside a cell but functions outside of it.