Tissue origin of serum placental-like alkaline phosphatase in cigarette smokers

A variety of solubilised tissue extracts from cigarette smokers and non-smokers have been screened quantitatively for both placental alkaline phosphatase (PLAP) and placental-like alkaline phosphatase (PLAP-like AP) in order to identify the possible tissue origins of the circulating PLAP-like AP found in most smokers. Lung alveolar tissue, and to a lesser extent colonic tissues, contained both PLAP-like AP and PLAP. Tissues from smokers and non-smokers contained comparable proportions and amounts of PLAP and PLAP-like AP. No other tissue source of PLAP-like AP was found other than those previously reported for testicular, endometrial and thymic tissue. Selective release of PLAP-like AP from the lung in cigarette smokers seems likely to be a major source for this isoenzyme in peripheral circulation.