The ability of high pressure to dissociate several peripheral protein- membrane complexes was investigated. Three vitamin K-dependent proteins (factor X, protein Z, and prothrombin) dissociated from small unilamellar vesicles (SUVs, 30 nm diameter) composed of 25% phosphatidylserine (PS) and 75% phosphatidylcholine (PC) at comparable pressures (midpoints of 0.3-0.6 kbar). The pressure-induced dissociation curves for the factor X-SUV interaction followed the expected behavior for an interaction with an apparent dissociation equilibrium constant at atmospheric pressure, K(D(atm)), of 9 x 10-7 M and a change in volume of association, ΔV(a), of 88 mL/mol. Factor X also dissociated from large unilamellar vesicles (LUVs, 100 nm diameter, 25% PS:75% PC) with a midpoint of 0.5 kbar. A second group of calcium-dependent membrane-binding proteins included protein kinase C (PKC), a 64-kDa protein, and a 32-kDa protein. The 32-kDa protein dissociated from SUVs (midpoint of 0.8 kbar), whereas PKC and the 64-kDa protein did not dissociate to a significant degree. The differences in dissociability of these proteins appeared to be a result of the differences in their K(D(atm))'s (decreased dissociability with decreased K(D(atm)). This pattern was further demonstrated by the relatively high midpoint of dissociation (1.1-1.4 kbar) of serum amyloid P component (SAP; K(D(atm)) ca. 10-11) and the limited dissociation of factor V(a) light chain (K(D(atm)) ca. 10- 11). Changing the vesicle composition to phosphatidylethanolamine in place of PC gave higher affinity and decreased dissociation of the 32-kDa protein and SAP. Thus, the susceptibility of various peripheral membrane-binding proteins to high pressure dissociation was governed by both the K(D(atm)) and the ΔV(a) of the particular protein-membrane interaction, with the ΔV(a)'s of the dissociable proteins being relatively small (<150 mL/mol).
|Original language||English (US)|
|Number of pages||10|
|State||Published - 1992|