Photosensitized electron transfer processes in SiO(2) colloids and sodium lauryl sulfate micellar systems: Correlation of quantum yields with interfacial surface potentials.

The effectiveness of negatively charged colloidal SiO(2) particles in controlling photosensitized electron transfer reactions has been studied and compared with that of the negatively charged sodium lauryl sulfate (NaLauSO(4)) micellar system. In particular, the photosensitized reduction of the zwitterionic electron acceptor propylviologen sulfonate (PVS(0)) with tris(2,2'-bipyridinium)ruthenium(II) [Ru(bipy)(3) (2+)] as the sensitizer and triethanolamine as the electron donor is found to have a quantum yield of 0.033 for formation of the radical anion (PVS([unk])) in the SiO(2) colloid compared with 0.

Photosensitized electron transport across lipid vesicle walls: Enhancement of quantum yield by ionophores and transmembrane potentials.

The photosensitized reduction of heptylviologen in the bulk aqueous phase of phosphatidylcholine vesicles containing EDTA inside and a membrane-bound tris(2,2'-bipyridine)ruthenium(2+) derivative is enhanced by a factor of 6.5 by the addition of valinomycin in the presence of K(+). A 3-fold stimulation by gramicidin and carbonyl cyanide m-chlorophenylhydrazone is observed.

Structure of the metal clusters in rabbit liver metallothionein.

Cadmium-113 nuclear magnetic resonance ((113)Cd NMR) has been used to determine the structures of the multiple cadmium binding sites in the two major isoproteins of rabbit liver metallothionein. The isotopically (113)Cd-labeled metallothionein used in these studies was isolated from the livers of rabbits that had been subjected to repeated injections of (113)CdCl(2). The native protein isolated from these livers contains an appreciable amount of Zn in addition to Cd, ranging from 2-3 mol per mol of protein out of a total metal content of 7 mol per mol of protein.

Determination by cadmium-113 nuclear magnetic resonance of the structural basis for metal ion dependent anticooperativity in alkaline phosphatase.

Cadmium-113 nuclear magnetic resonance (113Cd NMR) has been used to probe the binding characteristics of 113Cd2+ to the three classes of metal binding sites in Escherichia coli alkaline phosphatase to help elucidate the molecular origin of the metal ion dependent "half-sites" reactivity exhibited by this dimeric Zn2+ metalloenzyme [Otvos, J.D., Armitage, I.

Characterization of the properties of the multiple metal binding sites in alkaline phosphatase by carbon-13 nuclear magnetic resonance.

Carbon-13 nuclear magnetic resonance (13C NMR) of Escherichia coli alkaline phosphatase labeled biosynthetically with beta,beta-[gamma-13C]dideuteriohistidine has been used to determine the number and identity of the histidine residues that participate in metal ion coordination at the three classes of binding sites in this dimeric Zn2+ metalloenzyme. Detailed 13C NMR titrations of the apoenzyme with 113Cd2+ and Mg2+, in conjunction with parallel 13 Cd NMR measurements [Otvos, J.D.

Characterization of the histidine residues in alkaline phosphatase by carbon-13 nuclear magnetic resonance.

beta,beta-[gamma-13C]Dideuteriohistidine has been biosynthetically incorporated into alkaline phosphatase from Escherichia coli and utilized as a nonperturbing 13C nuclear magnetic resonance (NMR) probe of the environments of the histidine residues in this zinc metalloenzyme. The 13C NMR spectrum of the labeled enzyme exhibits 9 separate resonances arising from the 10 histidine residues located in each of the symmetrically disposed subunits of the dimer. The excellent resolution and large chemical shift range (14 ppm) displayed by these signals are direct consequences of the sensitivity of the histidine gamma-carbon chemical shift to the ionization state and tautomeric form of the imidazole side chains and the coordination of several of these to metal ion.

Photosensitized electron transport across lipid vesicle walls: quantum yield dependence on sensitizer concentration.

An amphiphilic tris(2,2'-bipyridine)ruthenium(2+) derivative that is incorporated into the walls of phosphatidylcholine vesicles photosensitizes the irreversible oxidation of ethylenediaminetetraacetate(3-) dissolved in the inner aqueous compartments of the vesicle suspension and the one-electron reduction of heptylviologen(2+) dissolved in the continuous aqueous phase. The quantum yield of viologen radical production depends on the phospholipid-to-ruthenium complex mole ratios. A kinetic model is used to derive an order-of-magnitude estimate for the rate constant of electron transport across the vesicle walls.

31P NMR of alkaline phosphatase. Saturation transfer and metal-phosphorus coupling.

The rate constants which characterize the formation and breakdown of the noncovalent (E.P) and covalent (E-P) enzyme-phosphate intermediates on the alkaline phosphatase reaction pathway are known to be sensitive to the nature of the metal ion bound to the enzyme. 31P NMR saturation transfer has been demonstrated to provide a simple and sensitive method for measuring the metal ion dependence of these rates under equilibrium conditions.

Plant crops as a source of fuel and hydrocarbon-like materials.

Chemical analyses have been made of a number of plant species in order to assess their suitability as renewable sources of hydrocarbon-like photosynthetic products. Yields of rubber and wax, glycerides, isoprenoids, and other terpenoids were estimated. Individual sterols were identified in latex from some species.