Document Detail

Processive interfacial catalytic turnover by Bacillus cereus sphingomyelinase on sphingomyelin vesicles.
MedLine Citation:
PMID:  12069857     Owner:  NLM     Status:  MEDLINE    
Sphingomyelinase (SMase), a water-soluble enzyme from Bacillus cereus, is shown to bind with high affinity to vesicles of sphingomyelin (SM) but not to vesicles of phosphatidylcholine (PC). The reaction progress by SMase bound to SM vesicles occurs in the scooting mode with virtually infinite processivity of the successive interfacial turnover cycles. Three conditions for the microscopic steady state during the reaction progress at the interface are satisfied: the bound SMase does not leave the interface even after all the SM in the outer layer is converted to ceramide; the SMase-treated vesicles remain intact; and the ceramide product does not exchange with SM present in excess vesicles or in the inner layer of the hydrolyzed vesicle. Within these constraints, on accessibility and replenishment of the substrate, the extent of hydrolysis in the scooting mode reaction progress is a measure of the number of vesicles containing enzyme. The slope of the Poisson distribution plot, for the enzyme per vesicle versus the logarithm of the fraction of the total accessible substrate remaining unhydrolyzed in excess vesicles, shows that a single 32 kDa subunit of SMase is fully catalytically active. The maximum initial rate of hydrolysis, at the limit of the maximum possible substrate mol fraction, X(S)*=1, is 400 s(-1) in H(2)O and 220 s(-1) in D(2)O, which is consistent with the rate-limiting chemical step. The integrated reaction progress suggests that the ceramide product does not codisperse ideally on the hydrolyzed vesicles. Furthermore, complex reaction progress seen with covesicles of SM+PC are attributed to slow secondary changes in the partially hydrolyzed SM vesicles.
Bao-Zhu Yu; David Zakim; Mahendra K Jain
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Publication Detail:
Type:  Journal Article; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Biochimica et biophysica acta     Volume:  1583     ISSN:  0006-3002     ISO Abbreviation:  Biochim. Biophys. Acta     Publication Date:  2002 Jun 
Date Detail:
Created Date:  2002-06-18     Completed Date:  2002-08-06     Revised Date:  2007-11-14    
Medline Journal Info:
Nlm Unique ID:  0217513     Medline TA:  Biochim Biophys Acta     Country:  Netherlands    
Other Details:
Languages:  eng     Pagination:  122-32     Citation Subset:  IM    
Department of Chemistry and Biochemistry, University of Delaware, Newark, USA.
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MeSH Terms
Bacillus cereus / enzymology*
Melitten / metabolism
Sphingomyelin Phosphodiesterase / metabolism*
Sphingomyelins / metabolism*
Grant Support
Reg. No./Substance:
0/Sphingomyelins; 20449-79-0/Melitten; EC Phosphodiesterase

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