Fluorimetric determination of tissue distribution and differences between the activity of aspirin esterases I and II in mice and rats

A modification of available fluorimetric methods, based on the native fluorescence of salicylic acid, has been used to assay the activity of aspirin esterases I and II in small amounts of several tissues from rats and mice. The results obtained showed that aspirin esterase I from mouse liver and kidney had the lowest activity and that the activity of aspirin esterase II from these organs was greater than that from the same organs from rats. Liver enzyme kinetics and tissue distribution in rats was shown to be similar to previous data obtained using a spectrophotometric method. This fluorimetric method, which is more sensitive and rapid than the spectrophotometric method, may be useful in studies on aspirin metabolism.