Preparation and crystal structure of [NEt4]3[Fe6W2S8(SEt)9]; structural and electrochemical comparisons with its molybdenum analogue

[NEt₄]₃[Fe₆M₂S₈(SEt)₉] (M = Mo or W) compounds are isomorphous and contain molybdenum and tungsten atoms in an essentially identical environment. These complexes undergo an irreversible one-electron oxidation at −0.46 V (Mo) and −0.51 V (W) and two one-electron reductions at −1.56 and −1.76 V (Mo) and −1.52 and −1.84 V (W), in DMSO solution versus (0.1 M). The only distinction between the behavior of these molybdenum and tungsten complexes identified thus far is that, for the former the reductions are reversible whereas for the latter they are irreversible. This difference may be relevant to the low activity found for nitrogenases reconstituted with tungsten in place of molybdenum.     

Specificity of nucleotide binding and coupled reactions utilising the mitochondrial ATPase

1. 1. Tightly bound ATP and ADP, found on the isolated mitochondrial ATPase, exchange only slowly at pH 8, but the exchange is increased as the pH is reduced. At pH 5.5, more than 60% of the bound nucleotide exchanges within 2.5 min.

2. 2. Preincubation of the isolated ATPase with ADP leads to about 50% inhibition of ATP hydrolysis when the enzyme is subsequently assayed in the absence of free ADP. This effect, which is reversed by preincubation with ATP, is absent on the membrane-bound ATPase. This inhibition seems to involve the replacement of tightly bound ATP by ADP.

3. 3. Using these two findings, the binding specificity of the tight nucleotide binding sites was determined. iso-Guanosine, 2′-deoxyadenosine and formycin nucleotides displaced ATP from the tight binding sites, while all other nucleotides tested did not. The specificities of the tight sites of the isolated and membrane-bound ATPase were similar, and higher than that of the hydrolytic site.

4. 4. The nucleotide specificities of ‘coupled processes’ nucleoside triphosphate-driven reversal of electron transfer, nucleoside triphosphate-³²P_i exchange and phosphorylation were higher than that of the hydrolytic site of the ATPase and similar to that of the tight nucleotide binding sites.

5. 5. The different nucleotide specificities of uncoupled ATP hydrolysis and coupled processes can be explained even if both processes involve a single common site on the ATPase molecule. This model requires that energy can be ‘coupled’ only when it is released/utilised in the nucleotide binding steps of the mechanism.

6. 6. Adenosine β,γ-imidotriphosphate (AMP-PNP) is not a simple reversible inhibitor of the ATPase, since incubation requires preincubation and is not reversed when the compound is diluted out, or by addition of ATP. This compound inhibits the isolated and membrane-bound ATPase equally well. Its guanosine analogue does not act in this way.

7. 7. In submitochondrial particles, ADP inhibited uncoupled hydrolysis of ATP much more effectively than coupled hydrolysis, the latter being measured both directly (from ATP hydrolysis in the absence of uncoupler) or indirectly, by monitoring ATP-driven reduction of NAD⁺ by succinate.

8. 8. The effects of ADP and AMP-PNP were interpreted as providing evidence for two of the intermediates in the proposed scheme for coupled triphosphate hydrolysis.

Fluorescent probes in model membranes. II. monolayer studies of 2,2′-(vinylenedi-p-phenylene)bisbenzoxazole, d-3-aminodesoxyequilenin and n-octadecylnaphthyl-2-amino-6-sulfonic acid with host-lipid tetradecanoic acid

Film studies at the air-water interface have been carried out for pure films of 2,2′-(vinylenedi-p-phenylene)bisbenzoxazole (VPBO), d-3-aminodesoxy-equlenin (EQ) and N-octadecylnapthyl-2-amino-6-sulfonic acid (ONS), and for mixed films with tetradecanoic acid for the first two fluorescent probes. Pure film isotherms indicate highly rigid non-monomolecular films for both VPBO and EQ, revealing the presence of strong intermolecular forces. In mixed films with tetradecanoic acid VPBO rapidly segregates with resultant film loss over a wide concentration range. EQ, however, can be stabilized by the host-lipid at low concentrations. This, coupled with an ability to only slightly affect the host-lipid liquid-condensed/liquid-expanded phase change, suggests that EQ can be regarded as “non-perturbing” and should be retained in condensed lipid phases.ONS, because of its unusual polar headgroup, resembled hexadecanoic acid more than octadecanoic acid. While difficulties in spreading ONS precluded the study of mixed films, the indications are that it would be a satisfactory expanded lipid state probe if mixing can be brought about.     

A spectrofluorimetric investigation of calf thymus DNA modified by BP diolepoxide and 1-pyrenyloxirane

7β,8α-Dihydroxy-9α,10α-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BP diolepoxide, $\text{1}$) and 1-pyrenyloxirane ($\text{2}$) bind chemically to calf thymus DNA. The fluorescence efficiency of pyrenyl groups in mutagen modified DNA varies appreciably with its conformation and decreases in the order: pyrenees, modified denatured DNA and modified native DNA. A particularly interesting observation is that the fluorescence efficiency of mutagen modified DNA intensifies substantially upon denaturation. Our results suggest that the pyrenyl groups in mutagen modified DNA are intercalated between the base pairs of DNA. Since both $\text{1}$ and $\text{2}$ are powerful frame-shifting mutagens for S. typhimurium TA-98, the intercalative covalent binding of these compounds to DNA may provide a molecular basis for their mutagenic activity.     

The action of the adenosylhomocysteine hydrolase inhibitor, 3-deazaadenosine,on phagocytic function of mouse macrophages and human monocytes

An inhibitor of adenosylhomocysteine hydrolase, 3-deazaadenosine, caused profound inhibition of phagocytosis of opsonized erythrocytes by mouse resident peritoneal macrophages $\text{in}\text{vitro}$. The inhibition was evident at concentrations as low as 2×10^?7M, and increased with increasing concentration and time of exposure to the analogue. It was not associated with detachment of the macrophage monolayers or with loss of cell viability. Although the inhibition was not reversible, progression of the functional impairment was interrupted by washing out the analogue. In striking contrast, phagocytic function of human blood monocytes was unaffected by 3-deazaadenosine.