Solubilization and Comparative Properties of Some Mammalian Diphosphopyridine Nucleosidases

Abstract

Abstract Diphosphopyridine nucleosidases (DPNases) were solubilized from acetone powders prepared from some mammalian tissues. Solubilization was effected by the action of porcine pancreatic lipase on DPNases that are resistant to solubilization by trypsin and which heretofore had not been solubilized. Molecular weight estimates made on DPNases obtained from porcine, bovine, sheep, dog, horse, mouse, rabbit, and human tissues, as well as mouse Ehrlich ascites tumor cells indicate that these enzymes fall into three size classes: porcine, bovine, and sheep, ∼25,000; dog, ∼50,000; and the remainder between 70,000 and 90,000. The electrophoretic characteristics of the DPNases indicate that with the exception of the sheep brain material all the low molecular weight enzymes migrate toward the cathode at pH 7.0. The sheep DPNase as well as the enzymes from all the other sources studied migrate in the opposite direction. The mouse ascites cell, rat, rabbit, and sheep preparations are particularly interesting in that they show a number of multiple forms that are enzymatically active. Notwithstanding the variability in molecular weight and electrophoretic mobility, the solubilized mammalian DPNases exhibit similar although not identical catalytic properties in their sensitivity to nicotinamide inhibition, specificity to DPN+ and TPN+, and formation of the 3-acetylpyridine analogue of DPN+. A new catalytic stain is described that is specific for DPNases which carry out the exchange reaction with pyridine bases.