Solubilization of acridine

Solubilization of an active H,K-ATPase is also a prerequisite for reconstitution of the enzyme into liposomes. With these H,K-ATPase proteoliposomes it is then possible to study the transport characteristics of pure H,K-ATPase, without the interference of residual protein contamination that is usually present in native vesicular H,K-ATPase preparations. Rabon et al. [118] first reported the reconstitution of choleate or n-octylglucoside solubilized H,K-ATPase into phosphatidylcholine-cholesterol liposomes. The enzyme was reconstituted asymmetrically into the proteoliposomes with 70% of the pump molecules having the cytoplasmic side extravesicular. In the presence of intravesicular K, the proteoliposomes exhibited an Mg-ATP-dependent H transport, as monitored by acridine orange fluorescence quenching. Moreover, as seen with native H,K-ATPase vesicles, reconstituted H,K-... 

A study by stopped-flow techniques of the rate of solubilization of positively charged acridine (and related) dyes by the micelles of several sodium n-alkyl sulphates was reported by Robinson and co-workers [132]. The solubilization process was relatively slow k = 47.6 s for acridine orange in NaDS) due largely to charge effects and the rate was very dependent on the geometrical shape... 

The preferred location of aromatic solutes in micelles cannot be learned unequivocally from the literature. Evidence has been presented for solubilization in the micelle core, at the surface, or at both these sites, depending on the concentration (43,199-204). Therefore the solubilization site of aromatic compounds seems to depend on details of the respective systems. In the case of the probe acridine, site information can be derived from relative quantum yields... 

Otherwise, the observed plateau could suggest an association of these aromatic amines with membrane components. In fact, it was shown that azido acridines do interact with proteins of submitochondrial particles (9) and that an acridine derivative covalently bounded to impermeable molecules did retain the uncouling property (10). Moreover, quinacrine is an inhibitor of the FI ATPase solubilized from bovine heart mitochondria (11) and this property can be extended to other kind of ATPase, like the calcium dependent enzyme purified from sarcoplasmic reticulum (12). 

When micelles form in the solution Ni is partitioned out of the bulk into the vicinity of the charged micelle surface. Binding of NiMu" is unlikely since the ion is hydrophilic and singly charged [89]. The nickel murexide systems, therefore, operate somewhat differently from indicator dyes such as Acridine Orange and Pinacyanol Chloride which are lipophilic and are either solubilized by the micelle or adsorbed on to the surface. The chromophore in the murexide system remains in the bulk phase. 

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