What are the only isoenzymes that retain activity when serum is heated to 65 degrees Celsius for 10 minutes?

The isoenzymes that retain activity when serum is heated to 65 degrees Celsius for 10 minutes are indeed the placental alkaline phosphatase (ALP) and the Regan isoenzyme. This characteristic is significant because high temperatures can inactivate many enzymes, including most forms of alkaline phosphatase, but certain isoenzymes exhibit resilience to thermal inactivation.

Placental ALP is produced in the placenta during pregnancy, and its activity is particularly relevant in certain diagnostic contexts, such as monitoring pregnancy and detecting placental disorders. The Regan isoenzyme, often associated with neoplastic processes, is not commonly found in normal tissues; its activity can indicate the presence of certain types of cancer, specifically those of the gonads and liver.

Understanding the thermal stability of these isoenzymes is crucial in clinical chemistry for interpreting laboratory results accurately, especially when differentiating between various sources of ALP elevation in the serum.