Assignment of the g = 4.1 EPR signal to manganese in the S2 state of the photosynthetic oxygen-evolving complex: an X-ray absorption edge spectroscopy study

X-ray absorption spectroscopy at the Mn K-edge has been utilized to study the origin of the g = 4.1 EPR signal associated with the Mn-containing photosynthetic O2-evolving complex. Formation of the g = 4.1 signal by illumination of Photosystem II preparations at 140 K is associated with a shift of the Mn edge inflection point to higher energy. This shift is similar to that observed upon formation of the S2 multiline EPR signal by 190 K illumination. The g = 4.1 signal is assigned to the Mn complex in the S2 state.     

Inhibition of chondrogenesis by normal mouse serum in cultured chick limb cells

Chick limb-bud mesoderm cells from embryonic stages 22–25 were cultured at high cell densities in media known to support chondrogenesis. Under these conditions the continuous presence of normal mouse serum, at a concentration of 10%, inhibits the ability of the cells to produce toluidine blue-stainable cartilage matrix materials. In contrast, mesodermal cells treated with comparable concentrations of other heterologous sera continue to differentiate much like the control cultures while growing in the presence of the test sera. The inhibitory effect of the serum was shown not to be the result of a general cytotoxic effect on protein synthesis or the inability of the cells to incorporate [³H]d-glucosamine. There was a significant difference however, in the distribution of the incorporated glucosamine. Less label was associated with the cell layer of the treated series, while a greater amount of the incorporated material was found to be secreted into the medium when compared with the control cultures. Studies have shown also that the serum inhibitory response is dose dependent, while the factor(s) itself is non-dialysable, stable to heat and repeated freezing and is not a conventional serum lipoprotein. Following the addition of whole or delipidated mouse serum, a significant increase in lipid droplets appears in the cytoplasm of the cells. Biochemical analyses of mouse serum-treated cells indicate that there is a marked increase in their triglyceride content as compared to the control cells. While the nature of the serum inhibitory factor remains to be determined, the accumulation of triglyceride following mouse serum treatment suggests that this may play a role in modulating the expression of the chondrogenic phenotype.     

Requirement for Abasic Endonuclease Gene Homologues in Arabidopsis Seed Development

Arabidopsis thaliana has three genes, Ape1L, Ape2, and Arp, that show homology to abasic (apurinic/apyrimidinic) endonuclease genes of bacterial, yeast, or animal cells. In bacteria, yeast, and animals, abasic endonucleases function in base excision repair of oxidized and other modified DNA bases. Here we report that plants with knock-out mutations in any one of Ape1L, Ape2, or Arp show no apparent differences from wild type in growth rate, growth habit, and fertility. However, coincident knock-out mutations in Ape1L and Ape2 are lethal and lead to abortion of developing embryos. Mutations of Arp are not deleterious, even in combination with one of the other two mutations. The results are consistent with the interpretation that the process of base excision repair, involving at least one intact copy of Ape1L or Ape2, is required in the process of embryogenesis.     

Antibiotic Exposure in a Low-Income Country: Screening Urine Samples for Presence of Antibiotics and Antibiotic Resistance in Coagulase Negative Staphylococcal Contaminants

Development of antimicrobial resistance has been assigned to excess and misuse of antimicrobial agents. Staphylococci are part of the normal flora but are also potential pathogens that have become essentially resistant to many known antibiotics. Resistances in coagulase negative staphylococci (CoNS) are suggested to evolve due to positive selective pressure following antibiotic treatment. This study investigated the presence of the nine most commonly used antimicrobial agents in human urine from outpatients in two hospitals in Ghana in relation to CoNS resistance. Urine and CoNS were sampled (n = 246 and n = 96 respectively) from patients in two hospitals in Ghana. CoNS were identified using Gram staining, coagulase test, and MALDI-TOF/MS, and the antimicrobial susceptibility to 12 commonly used antimicrobials was determined by disk diffusion. Moreover an analytical method was developed for the determination of the nine most commonly used antimicrobial agents in Ghana by using solid-phase extraction in combination with HPLC-MS/MS using electron spray ionization. The highest frequency of resistance to CoNS was observed for penicillin V (98%), trimethoprim (67%), and tetracycline (63%). S. haemolyticus was the most common isolate (75%), followed by S. epidermidis (13%) and S. hominis (6%). S. haemolyticus was also the species displaying the highest resistance prevalence (82%). 69% of the isolated CoNS were multiple drug resistant (≧4 antibiotics) and 45% of the CoNS were methicillin resistant. Antimicrobial agents were detected in 64% of the analysed urine samples (n = 121) where the most frequently detected antimicrobials were ciprofloxacin (30%), trimethoprim (27%), and metronidazole (17%). The major findings of this study was that the prevalence of detected antimicrobials in urine was more frequent than the use reported by the patients and the prevalence of resistant S. haemolyticus was more frequent than other resistant CoNS species when antimicrobial agents were detected in the urine.     

Correlation between nortriptyline and debrisoquine hydroxylation in the human liver

The benzylic hydroxylation of nortriptyline (NT) and debrisoquine (D) by isolated human liver microsomes from eight subjects was studied. There was a strong correlation between the 10-hydroxylation of NT and the 4-hydroxylation of D (r = 0.96). The ability to hydroxylate D was also measured in vivo as the ratio between D and 4-OH-D in urine after oral administration of the drug to four subjects. This estimate of hydroxylation capacity agreed with the in vitro measurements. Liver microsomes from a subject defined as a poor in vivo oxidizer of D hydroxylated NT and D unusually slowly. Separation of microsomal proteins by SDS-gel electrophoresis indicated a relative lack of a cytochrome P-450 isozyme with a molecular weight of 54,500 in the liver from the poor oxidizer.     

Characterization of the Earliest Known Staphylococcus aureus Plasmid Encoding a Multidrug Efflux System

The staphylococcal qacB-encoding multidrug resistance plasmid pSK156, isolated from a clinical strain dating from 1951, was characterized. Comparison of the regions flanking qacB with other qacA- and qacB-encoding plasmids provided insights into the evolution and dissemination of these multidrug efflux genes and led to the detection of the earliest known copy of the insertion sequence IS257.