Final answer:
The presence of catalase in the preparation of rough ER microsomes would indicate contamination, likely by peroxisomes, because catalase is not typically found in the rough ER.
Step-by-step explanation:
When isolating rough ER microsomes using ultracentrifugation, the presence of catalase would indicate contamination with another organelle. Catalase is an enzyme commonly found in peroxisomes, which function to break down hydrogen peroxide, a toxic by-product of metabolic processes. Thus, the presence of catalase in a fraction intended to be pure rough ER indicates that peroxisomes have also been isolated.
On the other hand, the presence of ribosomes, glycosylated proteins, and membranes would not necessarily indicate contamination. Ribosomes are naturally associated with the rough ER, as they bind to its surface and are responsible for protein synthesis. Glycosylated proteins are typically processed in the ER and the Golgi apparatus, so their presence might be expected to some extent. Similarly, membranes are a fundamental part of the rough ER structure. Therefore, their presence would not indicate contamination.