Enzyme compartmentation solubility

The compartmentation/solubility of an enzyme is another form of controlling the activity of an enzyme. 

Studies of the kinetics of [ S]0/ incorporation by C. sorokiniana (Giovanelli et al., 1978) and L. paucicostata (P. M. Macnicol, A. H. Datko, J. Giovanelli, and S. H. Mudd, unpublished) show that the soluble cysteine that is an intermediate on the pathway of sulfate assimilation is compartmentalized in a rapidly turning over pool which constitutes less than 2% of the total soluble cysteine in the cell. Recently it has been demonstrated that substantial portions of the cysteine synthases of leaves of spinach, peas and clover reside in the stroma of chloroplasts (Fankhauser ef al., 1976 Ng and Anderson, 1978). Chloroplastic and extrachloroplastic forms of cysteine synthase have been briefly reported (Fankhauser and Brunold, 1978). Earlier reports (Smith, 1972 Masada et al., 1975 Ascano and Nicholas, 1977) of cysteine synthase in a number of plant tissues claimed that the enzyme was predominantly soluble. The degree of intactness of the chloroplasts used in these studies was not determined, and a plausible explanation for recovery of cysteine synthase in the soluble fraction is that the chloroplasts were disrupted during isolation, releasing the enzyme. 

The biosynthesis of rubber may be divided into three steps (1) initiation, which requires an allylic diphosphate molecule, (2) elongation, in which IPP units are added to a Z-l,4-polyisoprene chain, and (3) termination, in which the polymer is released from the rubber transferase enzyme (Cornish, 1993). In plants, the elongation of Z-l,4-polyiso-prene (natural rubber) requires a small -allylic diphosphate initiator (less than or equal to C20). Famesyl pyrophosphate (FPP) is an effective initiator of polyisoprene biosynthesis (Light et al, 1989) further, because only one molecule of FPP is needed for each molecule of rubber formed, small traces of this substance that are inadvertently present complicate biosynthetic studies. The E-allylic diphosphates are hydrophilic cytosolic compounds, whereas Z-l,4-polyisoprene is hydrophobic and compartmentalized in subcellular rubber particles. A soluble E-prenyl transferase from the latex of Hevea brasiliensis serves as a famesyl diphosphate synthase and plays no direct role in elongation of Z-l,4-polyisoprene (Cornish, 1993). Because the hydro-phobic rubber molecule is produced inside a rubber particle but is formed from hydrophilic precursors from the cytoplasm, the polymerization reaction must take place at the particle surface. 

From the great number of oxidoreductases used to modify enzymatic BFC electrodes only a minority is capable of DET, which reduces the number of fuels and oxidants (Table 1). The substrate specificity of enzymes redners half-cell separation by e.g., membranes unnecessary. DET between enzyme and electrode also stops the need for soluble redox mediators to shuttle electrons between enzyme and electrode. This results in the possibility to design membraneless, non-compartmentalized enzymatic BFCs with a simple architecture. However, so far achieved DET currents are lower than MET currents, because usually only enzyme monolayers can be contacted. Strategies to improve the current density aim at the use of high surface area electrode materials like CNTs, AuNPs etc. or the layer-by-layer approach... 

Once established the chemical stability of the urea-urease reaction in the presence of lipids and of the fluorescent probe, the next step towards a successful oscillating system was the encapsulation of the enzyme into POPC liposomes through the droplet transfer method. This innovative method first takes advantage of the facile compartmentalization of water-soluble solutes (enzyme in this case) in water-in-oil (w/o) droplets, and then convert the solute-filled w/o droplets into vesicles that can be dispersed in an acidic solution of urea. 

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