Final answer:
Not all additives cause denaturation of phycocyanin. Those that do not affect the protein structure or function leave it intact, unlike the denaturing additives which disrupt the protein's bonds and conformation.
Step-by-step explanation:
The additives that did not denature the phycocyanin were likely those that did not affect the protein's structure or function. Proteins may be denatured by various treatments such as extremes in pH, high temperatures, or by the action of specific chemicals that disrupt the protein's bonds and structure. Not all additives cause denaturation; some may have no effect on the protein, possibly because they do not disturb the critical bonds within the protein's structure or the specific conditions required for the protein to maintain its conformation. In contrast, additives that do cause denaturation are different in that they interfere with the protein's native state, leading to a functional loss.