The most heat-labile fraction of alkaline phosphatase is obtained from which tissue?

The most heat-labile fraction of alkaline phosphatase is obtained from which tissue?

• A. Liver
• B. Bone
• C. Intestine
• D. Placenta

Answer: (B)

The test hinges on how alkaline phosphatase isoenzymes differ in heat stability. When serum is heated (e.g., 56°C for 10 minutes), some isoforms fade away while others resist heat. Placental ALP is notably heat-stable, so it remains active after heating, whereas the bone isoenzyme is the most heat-labile and loses activity readily. Therefore, the fraction that is most affected by heat—and thus originates from the tissue with the greatest heat sensitivity—comes from bone. Placental ALP, in contrast, stays active, and liver and intestinal isoforms are less labile than bone.

The test hinges on how alkaline phosphatase isoenzymes differ in heat stability. When serum is heated (e.g., 56°C for 10 minutes), some isoforms fade away while others resist heat. Placental ALP is notably heat-stable, so it remains active after heating, whereas the bone isoenzyme is the most heat-labile and loses activity readily. Therefore, the fraction that is most affected by heat—and thus originates from the tissue with the greatest heat sensitivity—comes from bone. Placental ALP, in contrast, stays active, and liver and intestinal isoforms are less labile than bone.