Phosphatidylinositol-specific phospholipase C forms different complexes with monodisperse and micellar phosphatidylcholine
2004 (English)In: Biochemistry, ISSN 0006-2960, E-ISSN 1520-4995, Vol. 43, no 7, 2080-2090 p.Article in journal (Refereed) Published
Phosphatidylinositol-specific phospholipase C (PI-PLC) from Bacillus cereus forms a premicellar complex E# with monodisperse diheptanoylphosphatidylcholine (DC7PC) that is distinguishable from the E* complex formed with micelles. Results are interpreted with the assumption that in both cases amphiphiles bind to the interfacial binding surface (i-face) of PI-PLC but not to the active site. Isothermal calorimetry and fluorescence titration results for the binding of monodisperse DC7PC give an apparent dissociation constant of K2 = 0.2 mM with Hill coefficient of 2. The gel-permeation, spectroscopic, and probe partitioning behaviors of E# are distinct from those of the E* complex. The aggregation and partitioning behaviors suggest that the acyl chains in E# but not in E* remain exposed to the aqueous phase. The free (E) and complexed (E# and E*) forms of PI-PLC, each with distinct spectroscopic signatures, readily equilibrate with changing DC7PC concentration. The underlying equilibria are modeled and their significance for the states of the PI-PLC under monomer kinetic conditions is discussed to suggest that the Michaelis−Menten complex formed with monodisperse DC7PC is likely to be E#S or its aggregate rather than the classical monodisperse ES complex.
Place, publisher, year, edition, pages
2004. Vol. 43, no 7, 2080-2090 p.
Biological Sciences Biochemistry and Molecular Biology
IdentifiersURN: urn:nbn:se:uu:diva-70078DOI: 10.1021/bi035063jOAI: oai:DiVA.org:uu-70078DiVA: diva2:97989