Endovesiculation of human erythrocytes exposed to sphingomyelinase C: a possible explanation for the enzyme-resistant pool of sphingomyelin.
When human erythrocytes are treated with Staphylococcus aureus sphingomyelinase C at 37 degrees C they become susceptible to cold lysis and appear to endovesiculate. Endovesiculation has been confirmed by showing that in parallel with sphingomyelin breakdown, the cells accumulate [3H]inulin or [14C]sucrose (without losing intracellular K+) and also experience a loss of cell-surface acetylcholinesterase activity into a latent intracellular pool which can be revealed by treatment with detergent. On the basis of these observations it can be calculated that endovesicles account for about 2-4% of cell volume and about 25% of total cell surface. Pretreatment of cells with bee venom phospholipase A2 completely blocked sphingomyelinase-induced endovesiculation but this effect was related to a concomitant decrease in sphingomyelin breakdown which was reduced by about 90%. These results indicate that the pool of sphingomyelin which is not susceptible to attack by sphingomyelinase C (about 15% of total sphingomyelin) may be resistant because of membrane internalisation and not because it originally resides in the inner leaflet of the plasma membrane.
Allan
D
D
Department of Experimental Pathology, University College London, U.K.
Walklin
C M
CM
D000110:Acetylcholinesterase / Q000097:blood; D001409:Bacillus cereus / Q000201:enzymology; D003080:Cold Temperature; D004912:Erythrocytes / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure*; D006461:Hemolysis; D006801:Humans; D007444:Inulin / Q000097:blood; D008854:Microscopy, Electron; D010713:Phosphatidylcholines / Q000097:blood; D010741:Phospholipases A / Q000494:pharmacology; D054467:Phospholipases A2; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism*; D013108:Sphingomyelin Phosphodiesterase / Q000378:metabolism* / Q000494:pharmacology; D013109:Sphingomyelins / Q000097:blood*; D013211:Staphylococcus aureus / Q000201:enzymology; D013395:Sucrose / Q000097:blood; D010738:Type C Phospholipases / Q000494:pharmacology
D010713:Phosphatidylcholines; D013109:Sphingomyelins; D013395:Sucrose; D007444:Inulin; D010741:Phospholipases A; D054467:Phospholipases A2; D000110:Acetylcholinesterase; D010727:Phosphoric Diester Hydrolases; D010738:Type C Phospholipases; D013108:Sphingomyelin Phosphodiesterase