Bismuth compounds are known for their low levels of toxicity in mammals, and various types of bismuth salts have been used to treat medical disorders. As part of our program to probe this aspect of bismuth chemistry, cyclic organobismuth compounds 1 to 8 bearing a nitrogen or sulfur atom as an additional ring member have been synthesized, and their antimicrobial activities against five standard strains of gramnegative and gram-positive bacteria were assessed. The eight-membered-ring compounds, compounds 1 to 3, exhibited MICs of less than 0.5 g/ml against Staphylococcus aureus and were more active than the sixmembered ones, compounds 5 to 8 (MICs, 4.0 to 16 g/ml). The gram-positive bacteria (Staphylococcus aureus, Bacillus subtilis, and Enterococcus faecalis) were more susceptible to both types of ring compounds than the gram-negative ones (Escherichia coli and Pseudomonas aeruginosa). Treatment with polymyxin B nonapeptide increased the susceptibility of E. coli to cyclic organobismuth compounds, indicating the low permeability of the outer membrane of gram-negative bacteria to the compounds. Compound 1 also had activity against methicillin-resistant S. aureus, which had an MIC for 90% of the hospital stock strains of 1.25 g/ml. The killing curves for S. aureus treated with compound 1 or 3 revealed a static effect at a low dose (2؋ the MIC). However, when S. aureus was treated with 10؋ the MIC of compound 1 or 3, there was an approximately 3-log reduction in the viable cell number after 48 h of treatment. Electron microscopic inspection demonstrated a considerable increase in the size of S. aureus and the proportion of cells undergoing cell division after treatment with compound 1 at 0.5؋ the MIC.
A mouse DNA polymerase accompanied by a novel RNA polymerase activity and its specific protein factor (stimulating factor) were purified from Ehrlich ascites tumor cells and partially characterized. The DNA polymerase was thought to be a subspecies of DNA polymerase alpha, and to be accompanied by or copurified with RNA polymerase activity capable of synthesizing RNA, which was probably utilized as a primer for subsequent DNA polymerization on a template of poly(dT) or poly(dC). This coupled reaction by RNA and DNA polymerase activities required the stimulating factor in addition to ribo- and deoxyribonucleotide substrates, although the degree of requirement depended on the kind of template and ribonucleotide substrate: the activity to incorporate dATP with poly(dT) plus ATP depended greatly on the stimulating factor, while the activity to incorporate dGTP with poly(dC) did not when GTP was added at high concentrations. GDP could be substituted for GTP, but the activity with poly(dC) plus GDP depended largely on the stimulating factor. Involvement of known RNA polymerases in the activity with poly(dT) was excluded, because addition of purified mouse RNA polymerases I and II had no effect on the incorporation of dATP, and alpha-amanitin (100 micrograms/ml) did not inhibit the incorporations of dATP and ATP. Analysis of the inhibition by the nucleotide analog 2',3'-dideoxynucleoside 5'-triphosphate (ddNTP) further supported the involvement of new RNA polymerase; ddNTPs inhibited the activities with poly(dT) and poly(dC) significantly more than RNA polymerases I and II or DNA polymerase alpha activity with poly(dT) . oligo(rA) and poly(dC) . oligo(dG) as template. Lineweaver-Burk analysis of the inhibitions showed that ddATP inhibited competitively with respect to ATP, and ddGTP inhibited competitively with respect to GDP but noncompetitively with respect to GTP.
The LH1 antenna complex and a native form of the LH2 complex were isolated from the carotenoidless R26 and R26.1 mutants of Rhodobacter sphaeroides by the use of a new detergent, sucrose monocholate. One-color, pump-and-probe transient Raman spectroscopy of these complexes using 351 nm, approximately 50 ps pulses showed the generation of the triplet state of bacteriochlorophyll a (BChl a), whereas measurements using 355 nm, approximately 12 ns pulses showed the generation of BChl a cation radical. Subpicosecond to nanosecond time-resolved absorption spectroscopy using 388 nm, 200 fs pulses for excitation showed rapid (<1 ps) generation of the triplet state and fast decay (<10 ps) of the singlet state of BChl a. Microsecond absorption spectroscopy confirmed the generation of BChl a cation radical. EPR spectroscopy using 532 nm, approximately 5 ns pulses for excitation established the generation of BChl a cation radical. The EPR line width suggested that the unpaired electron is shared by two BChl a molecules. In LH1, the yield of BChl a cation radical per complex was estimated to be about 80% of that in the reaction center, and in LH2 about 50%. Thus, rapid generation of the triplet state, and its subsequent transformation into the cation-radical state of BChl a have been shown to be intrinsic properties of B870 and B850 BChl a assembly in the carotenoidless LH1 and LH2 antenna complexes. In the case of the carotenoid-containing LH2 complex, the triplet states of BChl a and carotenoid (spheroidene) were generated immediately after excitation, but the triplet-state BChl a was quenched efficiently by the carotenoid so that no BChl a cation radical was generated. Thus, the photoprotective function of the carotenoid in this antenna complex is shown.
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