Phosphatidylcholine and 4-methylumbelliferyl phosphorylcholine hydrolysis by purified placental sphingomyelinase.
We present evidence which indicates that highly purified placental acid sphingomyelinase hydrolyses [14C]phosphatidylcholine [( 14C]PC) and the synthetic phosphodiester 4-methylumbelliferyl phosphorylcholine (4-MUPC). Hydrolysis was achieved by phospholipase C phosphodiesterase action. Of the several detergents tested, sodium taurocholate alone was necessary for PC hydrolysis, while 4-MUPC was hydrolysed independent of any detergent requirement. The pH optima for the reactions were 4.6-4.8 for PC hydrolysis and 4.8-5.0 for 4-MUPC hydrolysis. As with sphingomyelin hydrolysis, degradation of both PC and 4-MUPC was inhibited by 5'-, 3'-, and 2'-AMP, 5'-AMP being the most effective of the three. Furthermore, the phosphodiesterase activity against PC and 4-MUPC copurified with sphingomyelinase from human placenta and cross-reacted with a specific anti-sphingomyelinase monoclonal antibody, strongly indicating identity of the phosphodiesterases. This explains phospholipase C deficiency in sphingomyelinase-deficient Niemann-Pick disease cells.
Freeman
S J
SJ
Shankaran
P
P
Wolfe
L S
LS
Callahan
J W
JW
D000227:Adenine Nucleotides / Q000494:pharmacology; D002250:Carbon Radioisotopes; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007700:Kinetics; D010713:Phosphatidylcholines / Q000378:metabolism*; D010742:Phospholipid Ethers; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism*; D010920:Placenta / Q000201:enzymology*; D011247:Pregnancy; D011663:Pulmonary Surfactants / Q000378:metabolism*; D013108:Sphingomyelin Phosphodiesterase / Q000378:metabolism*; D013379:Substrate Specificity; D010738:Type C Phospholipases / Q000378:metabolism
D000227:Adenine Nucleotides; D002250:Carbon Radioisotopes; D010713:Phosphatidylcholines; D010742:Phospholipid Ethers; D011663:Pulmonary Surfactants; C046258:4-methylumbelliferyl phosphorylcholine; D010727:Phosphoric Diester Hydrolases; D010738:Type C Phospholipases; D013108:Sphingomyelin Phosphodiesterase