Which isoenzymes retain activity after serum heating to 65 degrees Celsius for 10 minutes?

The correct answer is the option mentioning placental ALP and Regan isoenzyme because these isoenzymes have a higher thermal stability compared to others in the alkaline phosphatase (ALP) family. When serum is heated to 65 degrees Celsius for 10 minutes, many proteins and enzymes denature and lose their activity. However, placental ALP and Regan isoenzyme are notable exceptions due to their modified structure, which makes them less susceptible to heat-induced denaturation.

Placental ALP is primarily produced by placental tissue and is often used as a tumor marker in certain cancers. The Regan isoenzyme is an atypical form of ALP that can be associated with various malignancies, including ovarian and lung cancers. Their unique properties allow them to remain active even under conditions that would typically cause other enzymes to lose function.

In contrast, options involving bone ALP, pseudcholinesterase, and liver ALP generally do not retain activity at elevated temperatures due to their more conventional structural characteristics that are sensitive to heat. Understanding the thermal stability of these isoenzymes is important in clinical laboratory settings to ensure accurate enzyme activity measurements and interpretations.