The Physiological Actions of Bacterial Phospholipases C on Eucaryotic Cells and their Membranes

Publisher Website
Google Scholar
Abstract
The hydrolytic and hemolytic actions of bacterial phosphatidylcholine-hydrolyzing phospholipases C and sphingomyelinases C on the micellar phospholipids, mammalian erythrocytes and their ghosts are described and discussed in detail. The substrate specificity of each phospholipase C, the accessibility of these enzymes to the erythrocyte membrane, and divalent metal ions such as Ca2+ and Mg2+, are the important or essential factors for the actions of these enzymes. Especially, the contributions of Ca2+ and Mg2+ are of significance. With some exceptions, Ca2+ is stimulative or essential for the hydrolytic and hemolytic actions of phosphatidylcholine-hydrolyzing phospholipases C, while Mg2+ is stimulative but Ca2+ is inhibitory for those actions of sphingomyelinases C. In the action of Bacillus cereus sphingomyelinase C, the enzyme is specifically adsorbed onto the surface of various erythrocytes, in the presence of Ca2+. For the explanation of the specific role of these divalent metal ions, the formation of ternary enzyme-metal ion-substrate complex is postulated in the physiological actions of phospholipases C and discussed in detail. Also, the in vitro and in vivo actions of bacterial phosphatidyl-inositol-specific phospholipases C are described and discussed. These enzymes release the ectoenzymes such as alkaline phosphatase, 5′-nucleotidase and acetyl-cholinesterase from the plasma membrane of mammalian or tumor cells. In this context, the antitumor activity of phosphatidylinositol-specific phospholipases C of Bacillus sp. toward transplanted Sarcoma 180 cells is described, and the deformation of these cells in vivo is shown by scanning electronmicroscopy.