Single-chain

While most vesicles are formed from double-tail amphiphiles such as lipids, they can also be made from some single chain fatty acids [73], surfactant-cosurfactant mixtures [71], and bola (two-headed) amphiphiles [74]. In addition to the more common spherical shells, tubular vesicles have been observed in DMPC-alcohol mixtures [70]. Polymerizable lipids allow photo- or chemical polymerization that can sometimes stabilize the vesicle [65] however, the structural change in the bilayer on polymerization can cause giant vesicles to bud into smaller shells [76]. Multivesicular liposomes are collections of hundreds of bilayer enclosed water-filled compartments that are suitable for localized drug delivery [77]. The structures of these water-in-water vesicles resemble those of foams (see Section XIV-7) with the polyhedral structure persisting down to molecular dimensions as shown in Fig. XV-11. 

This inequality indicates the amphiphile adopts a shape essentially equivalent to that of a cone with basal area <3. Such cones self-assemble to fonn spheroidal micelles in solution or spheroidal hemimicelles on surfaces (see section C2.3.15). Single-chain surfactants with bulky headgroups, such as SDS, typify surfactants in this category. 

P-MnOj pyrolusite (8) single chains of edge-shared (MnO ) octahedra (1x1 channels)... 

Thaumatin. Thaumatin [53850-34-3] is a mixture of proteins extracted from the fmit of a West African plant, Thaumatococcus daniellii (Beimett) Benth. Work at Unilever showed that the aqueous extract contains two principal proteins thaumatin I and thaumatin II. Thaumatin I, mol wt 22,209, contains 207 amino acids in a single chain that is cross-linked with eight disulfide bridges. Thaumatin II has the same number of amino acids, but there are five sequence differences. Production of thaumatins via genetic engineering technology has been reported (99). 

Calcitonins from several species have been characteri2ed and synthesi2ed. They are all single-chain 32-residue polypeptides (ca 3600 mol wt), although a disulfide link between the first and seventh cysteine residues results in a cycHc stmcture that is indispensable for activity (Eig. 6). 

Factor V. High in sialic acid content. Factor V is a large asymmetric single-chain glycoprotein that becomes an active participant in the coagulation cascade when it is converted to its active form by a-thrombin. Approximately 25% of human Factor V is found in the whole blood associated with platelets. Factor V is an essential cofactor along with Factor Xa plus phosphohpid plus Ca " in the conversion of prothrombin to thrombin. 

Factor VII. This is a vitamin K-dependent serine protease that functions in the extrinsic coagulation pathway and catalyzes the activation of Factors IX and X. Factor VII is present constitutively in the surface membrane of pericytes and fibroblasts in the adventitia of blood vessels, vascular endothehum, and monocytes. It is a single-chain glycoprotein of approximately 50,000 daltons. 

Protein S. Protein S is a single-chain molecule of approximately 78,000 daltons that contains 10 y-carboxy glutamic acid residues in the NH -terminal portion of the molecule. Protein S is a regulatory vitamin K-dependent protein. In plasma 40% of this protein circulates free and 60% circulates bound to C4b binding protein. Free Protein S functions as a nonenzymatic cofactor that promotes the binding of Protein C to membrane surfaces (22—25). 

Fig. 4. Fibrinolytic system where SCUPA is single-chain urokinase plasminogen activator rTPA is recombinant tissue plasminogen activator APSAC is acylated plasminogen streptokinase activator complex SK is streptokinase and UK is urokinase.

Streptokinase. Streptokinase is a single-chain protein containing 415 amino acids, mol wt of 45,000 to 50,000 (261,284—286). It is produced by P-hemolytic streptococci and is not an enzyme per se. Only after streptokinase combines with plasminogen on a 1 1 basis to form a... 

Prourokinase is a single-chain protein containing 411 amino acids (261,265,274,275). In clinical uses scu-PA does not bind to fibrin only and its use causes a decreased plasma fibrinogen of 80%. Its half-life in the circulation is 5 min. It is cleared by the fiver. It is used at 40—70 mg over 1 h and heparin is needed simultaneously. Fibrin specificity and thrombolytic efficacy are similar to that of t-PA. 

Streptokinase has a molecular weight of about 47,000 with a single chain of 415 amino acids there are no intramolecular disulfide bonds (64). The complete nucleotide sequence of the gene encoding the RNA for this protein has been reported (65,66). 

Fig. 63. Molecular arrangement in (a, c) plane of a mixed ethylene-chlorine binary crystal illustrating (a) radical pair formation, (b) single chain growth and (c) chain growth in the vicinity of product line. Molecules labelled 1-4 are ethylene (C2H4), chlorine, chloroethyl radical (C2H4CI) and anti 1,2-dichloroethane (C2H4CI2), respectively.

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