Triglyceride formation and hydrolysis by toad bladder epithelium.

Triglycerides of toad bladder epithelium have been labeled in vitro with either palmitate-1-(14)C or linoleate-1-(14)C, during incubation of bladders that had been cut in halves. Hydrolysis with pancreatic lipase of triglycerides labeled in this fashion revealed that palmitate-1-(14)C appeared predominantly in the 1- and 3-position, whereas half of linoleate-1-(14)C was located in the 2-position. The hydrolysis of palmitate-1-(14)C or linoleate-1-(14)C labeled triglycerides was examined in homogenates of isolated bladder mucosal cells. Lipase activity was evident from pH 3.5 to 8.0, but clearly greatest at pH 4.5. Below pH 6.0 the products of hydrolysis were fatty acid and monoglyceride and the 1- (or 3-) position was preferentially attacked; above pH 6.0 complete deacylation occurred. Acid-optimum hydrolysis of triglycerides with production of monoglycerides was linear for about 30 min. After 2 hr most of the labeled triglycerides were hydrolyzed. Repeated freezing and thawing of the homogenate enhanced lipase activity. Added Ca(++), previously shown to be required for phospholipase A activity in toad bladder, had no effect on hydrolysisof triglycerides. This lipase activity directed at the considerable store of triglycerides present in toad bladder epithelium may provide fatty acid for energy production or for synthesis of other esters such as in phospholipids.