Document Detail

Phospholipase A2 at the bilayer interface.
MedLine Citation:
PMID:  1866429     Owner:  NLM     Status:  MEDLINE    
Interfacial catalysis is a necessary consequence for all enzymes that act on amphipathic substrates with a strong tendency to form aggregates in aqueous dispersions. In such cases the catalytic event occurs at the interface of the aggregated substrate, the overall turnover at the interface is processive, and it is influenced the molecular organization and dynamics of the interface. Such enzymes can access the substrate only at the interface because the concentration of solitary monomers of the substrate in the aqueous phase is very low. Moreover, the microinterface between the bound enzyme and the organized substrate not only facilitates formation of the enzyme-substrate complex, but a longer residence time of the enzyme at the substrate interface also promotes high catalytic processivity. Binding of the enzyme to the substrate interface as an additional step in the overall catalytic turnover permits adaptation of the Michaelis-Menten formalism as a basis to account for the kinetics of interfacial catalysis. As shown for the action of phospholipase A2 on bilayer vesicles, binding equilibrium has two extreme kinetic consequences. During catalysis in the scooting mode the enzyme does not leave the surface of the vesicle to which it is bound. On the other hand, in the hopping mode the absorption and desorption steps are a part of the catalytic turnover. In this minireview we elaborate on the factors that control binding of pig pancreatic phospholipase A2 to the bilayer interface. Binding of PLA2 to the interface occurs through ionic interactions and is further promoted by hydrophobic interactions which probably occur along a face of the enzyme, with a hydrophobic collar and a ring of cationic residues, through which the catalytic site is accessible to substrate molecules in the bilayer. An enzyme molecule binds to the surface occupied by about 35 lipid molecules with an apparent dissociation constant of less than 0.1 pM for the enzyme on anionic vesicles compared to 10 mM on zwitterionic vesicles. Results at hand also show that aggregation or acylation of the protein is not required for the high affinity binding or catalytic interaction at the interface.
F Ramirez; M K Jain
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, P.H.S.; Review    
Journal Detail:
Title:  Proteins     Volume:  9     ISSN:  0887-3585     ISO Abbreviation:  Proteins     Publication Date:  1991  
Date Detail:
Created Date:  1991-09-12     Completed Date:  1991-09-12     Revised Date:  2007-11-15    
Medline Journal Info:
Nlm Unique ID:  8700181     Medline TA:  Proteins     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  229-39     Citation Subset:  IM    
Department of Chemistry, SUNY, Stony Brook 11794.
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MeSH Terms
Binding Sites
Lipid Bilayers*
Models, Molecular
Pancreas / enzymology*
Phospholipases A / chemistry*
Phospholipases A2
Protein Conformation
Grant Support
Reg. No./Substance:
0/Lipid Bilayers; EC 3.1.1.-/Phospholipases A; EC A2

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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