Electroactivity of adsorbed prothrombin at the Hg/solution interface and relation with the nature of the adsorption states

Interaction of an amphitropic protein (factor Xa) with membrane models in a complex system

Phosphatidylserine (PS) plays a crucial role, in the conversion of prothrombin into thrombin by the protease, factor Xa. Physiologically, the conversion occurs in the prothrombinase complex. The question of how water-soluble proteins that normally circulate in plasma bind remains to be unambiguously determined. We previously found that the amphitropic proteins (prothrombin, factors V and Va) penetrate into phospholipid layers. AC polarography has allowed the detection for the first time of insertion of factor Xa into condensed monolayers containing phosphatidylserine (PS) and phosphatidylcholine (PC) either 100% PS or 25% PS in the presence of Ca2+. This observation demonstrates that part of factor Xa can cross the phospholipid polar headgroup/hydrocarbon chain interface. In parallel experiments, radioactive surface measurements permitted measuring binding of tritium-labeled factor Xa onto a PS monolayer and calculate an association constant, 6x10(6) M(-1). Penetration of factor Xa into PS-containing vesicles was investigated also using photoactivable 5-[125I]iodonaphthalene-1-azide, which binds selectively to the lipid embedded domains of the protein. These experiments suggest that Factor Xa penetrates preferentially by its heavy chain, an alternative mode of binding to the commonly accepted binding via its Gla domain. Interaction of factor Xa with PS vesicles also changes its apparent K(m) for S 2222.

Experimental methods for investigating protein adsorption kinetics at surfaces

The adsorption of proteins at the solid-liquid interface is a process of fundamental importance in nature. Extensive reviews (MacRitchie, 1978; Andrade & Hlady, 1986; Norde, 1986) testify to the strong interest which has been shown in the problem during the past few decades. Norde & Lyklema (1978) have rightly pointed out that protein adsorption is scientifically intriguing; the phenomenology is complicated and includes many presently apparently irreconcilable observations.

Influence of surface charge on adsorption of fibrinogen and/or albumin on a rotating disc electrode of platinum and carbon

The adsorption of fibrinogen on to platinum and carbon and of albumin on to carbon was investigated for various changes of the surface by recording the variations of the double-layer capacitance of the electrochemical interface during adsorption, as a function of time. The rate of the second step of the adsorption decreased with increasing negative charge on to platinum but was charge-independent on to carbon. In contrast, on both surfaces, the rate of the first step and the area of the electrode surface in close contact with adsorbed proteins were both found to increase with increasing negative charge of the surface, although at pH 7.4 albumin and fibrinogen are negatively charged. The hypothesis of ion coadsorption inside the proteic layer has been proposed to account for this result.

Interaction of human gamma-carboxyglutamic acid domainless prothrombin with phospholipids

The conversion of prothrombin into thrombin occurs at the surface of stimulated platelets. In order to see the influence of gamma-carboxyglutamic acid in the interaction of prothrombin with phospholipid, we investigated the direct interaction of the peptide 1-41 and prothrombin (des 1-44) with phospholipid monolayers of various compositions. Adsorption of the labeled proteins was determined by surface radioactivity measurements. Penetration of the proteins into the lipid layers was inferred from capacitance variation of the monolayer, measured by a.c. polarography. Prothrombin (des 1-44) was found both to adsorb and to penetrate the lipid monolayers, in the presence and in the absence of Ca++. The effects are higher on 100% PS than on 25% PS. This protein was also found to increase the permeability of vesicles containing 25% PS to T1+ ions, in the presence and in the absence of Ca++. Comparison with prothrombin shows that Gla residues are clearly involved in the interaction at 25% PS; nevertheless, the peptide 1-41 does not penetrate. A model of interaction of prothrombin with phospholipid, including both adsorption of prothrombin by Gla residues and its penetration by another domain, is proposed.

Interaction of alpha-thrombin and prethrombin 2, with phosphatidylserine-containing monolayers

Prothrombin activation complex is located at a phospholipid surface on activated platelets. To see whether the thrombin domain of the molecule plays a role in the interaction with lipids, we investigated the direct interaction of human alpha-thrombin and its precursor prethrombin 2 with phospholipid monolayers of various compositions (PS/PC). Adsorption of the labeled proteins was determined by surface radioactivity measurements. Penetration of the proteins in the lipid layer was inferred from capacitance variation of the monolayer, measured by a.c. polarography. Disulfide bridges reduced at the electrode were determined by cyclic voltametry. In all the cases studied, although in different manners thrombin was found both to adsorb and penetrate the lipid layer, whereas prethrombin 2 did not penetrate pure phosphatidylcholine (PC). In the case of thrombin, but not of prethrombin 2, penetration is accompanied by S-S reduction which is maximum at 10 per cent of phosphatidylserine (PS). This indicates a different orientation for prethrombin 2 and thrombin in the lipid layer. This observation might be of importance for the comprehension of the architecture of the prothrombin activation complex and for the regulation of thrombin formation within the complex.