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Proton nuclear resonance spectra at 250 MHz of plastocyanins from spinach (Spinacia oleracea) and a blue green alga (Anabaena variabilis) are reported. Spectra of the reduced plastocyanins contain well-resolved peaks from slowly exchangeable N-H, histidine C2-H tyrosine ring, peptide alpha-CH, and high-field protons. The widths of these peaks indicate that the plastocyanins are monomeric. When the plastocyanins are oxidized, several changes in the spectra are observed including disappearance of peaks assigned to two histidine side chains. The pKa' values of the two histidine residues of reduced spinach plastocyanin are abnormally low (4.9 and less than 4.5). These pKa' values become more normal in apoplastocyanin or plastocyanin inhibited by cyanide. The results suggest that the imidazole groups of the two histidine residues are liganded directly to the copper in plastocyanin. The displacement of copper by cyanide is reversed at low pH. Spectra of apo- and reduced plastocyanins show only minor differences. However, the slowly exchangeable protons of plastocyanin exchange more rapidly in the apoprotein. Copper binding apparently does not cause a major reorganization of the protein structure, but the presence of copper does stabilize this structure.

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The multi-mode chemical-electric propulsion capable energetic ionic liquid propellant [Emim][EtSO 4 ]-HAN is electrosprayed in a 100 μm capillary emitter to test the electricmode performance of the propellant. The ionic liquid exhibits stable electrospray emission in both cation and anion extraction modes at a nominal extraction voltage of 3400 V. Near field measurements of current and mass flow rate distribution are taken at flow rates from 0.19 nL/s to 3.06 nL/s. Total emission current, as measured by Faraday cup and integrated, increases from 754 nA to 3195 nA for cation emission and from 552 nA to 2012 nA for anion emission. The thrust and specific impulse at 0.19 nL/s flow rate is 1.08 μN and 412 seconds, respectively, with a beam power of 2.22 mW. At 3.06 nL/s, the thrust is 8.71 μN and the specific impulse is 204 seconds with a beam power of 8.85 mW. Extrapolation of the current data shows that specific impulse in excess of 1000 seconds is achievable through optimized feed system and emitter design.

Chloroplast membrane carboxyl groups were modified by carbodiimide activation followed by glycine methyl ester substitution, leaving the derivatized group uncharged. This charge alteration induced a number of effects similar to addition of salts to control chloroplasts suspended in a low salt medium. These include: (a) restacking or multiple membrane association in low salt-treated chloroplasts that lack grana stacks, (b) Polycations are potent inhibitors of chloroplast photosystem I electron transfer reactions, when applied under low salt conditions (2, 3). Chloroplasts held in 0.1 M KCI do not show inhibition of electron flow by polycations (3); rather, polycations inhibit photophosphorylation and stimulate electron flow to some extent and greatly stimulate H+ ion fluxes (7). Knowing that chloroplast lamellae membranes have a net negative charge (8), it is probable that the polycation effects in both cases are mediated via electrostatic interactions between the membrane surface and the added polycation. Why does high salt media prevent the PS2 I inhibition seen in low salt media? Perhaps the prevention of polycation inhibition is due to screening of fixed negative charges by the soluble ions, i.e. the reduction in the membrane surface charge, resulting in less tight polycation binding. Another possibility is that the membrane conformation is quite different in the low and high salt cases, keeping the critical "site" of inhibition masked in the high salt media.Izawa and Good (14) (9) have shown that high salt conditions and grana stacking in mutant Chlamnydomonas cells that normally do not show in vivo stacking. They concluded that the large particle revealed by freeze etching is associated with the capacity of the membrane to exhibit stacking. Freeze etch results (1,19) show that completely unstacked spinach chloroplast membranes can retain the large particle, so unstacking does not coincide with its disappearance, although the presence of this particle may be a necessary condition for stacking to occur.We understand neither the mechanism of chloroplast membrane association nor the role of fixed charges in membrane structure and function. Inasmuch as the polylysine inhibition of PSI probably involves electrostatic interaction with fixed negative charge sites, we investigated the effects of masking membrane carboxyl groups on polylysine inhibition, on membrane conformational changes (acid-and salt-induced), and on grana stacking. Following Hoare and Koshland (12), we modified chemically the surface carboxyl groups, substituting glycine methyl ester in place of the carboxyl group. Figure 1 describes this modification. The glycine methyl ester replaces the carboxyl negative group and the adduct is electrically neutral, as the amide group has a very low pK. In this way, we have a test of the hypothesis that polylysine inhibits PSI by binding to carboxyl groups, and a system for investigating the role of carboxyl groups in grana stacking and membrane conformational changes.