The fish diet of black-browed albatrossDiomedea melanophris and grey-headed albatrossD. Chrysostoma at South Georgia

 The fish component of the diet of black-browed and grey-headed albatrosses at South Georgia was investigated by intercepting 155 meals from adults arriving to feed chicks during February 1986 and 1994. Fish represented 30% and 72% by mass of the diet of black-browed albatrosses and 14% and 60% by mass of the diet of grey-headed albatrosses in 1986 and 1994 respectively. We determined the identity and quantified the contribution (by numbers, size and mass) of fish species mainly by using otoliths (54 representing 9 taxa and 57 representing 17 taxa in black-browed and grey-headed albatross samples respectively). For black-browed albatrosses in 1986 the main fish prey was Patagonotothen guntheri (77% of otoliths, 51% of estimated fish biomass) and a single large specimen of Icichthys australis (40% estimated biomass), whereas in 1994 Pseudochaenichthys georgianus was the main fish prey (57% of estimated biomass) with Magnisudis prionosa (30%) and Champsocephalus gunnari (12%) also making substantial contributions. Grey-headed albatross samples from 1986 were dominated by southern lampreys (40% by number, 79% of estimated biomass), lanternfish (32% of numbers, 9% by mass) and Patagonotothen guntheri (11% by mass); in 1994 Champsocephalus gunnari (42% by numbers, 24% by mass), Magnisudis prionosa (13% by number, 36% by mass), Muraenolepis microps (90% by number), Pseudochaenichthys georgianus (15% by mass) and lanternfish (18% by number but only 1% by mass) were the main prey. The importance of Patagonotothen guntheri to both species in 1986 and its absence in 1994 probably reflect albatrosses obtaining it from the commercial fishery, which was active in 1986 but closed in 1994. Otherwise the fish diet of black-browed albatrosses is dominated by krill-feeding fish, characteristic of the waters of the South Georgia shelf. In contrast, the grey-headed albatross diet comprises deeper water mesopelagic species, especially lanternfish, which reflect its affinity for the Antarctic Polar Frontal Zone and associated oceanic upwellings. Received: 28 June 1995 / Accepted: 8 October 1995     

Thermodynamic resolution of the iron-sulfur centers of the succinic dehydrogenase of Rhodopseudomonas sphaeroides.

A single alkaline wash removes most of the succinic dehydrogenase activity from chromatophores of Rhodopseudomonas sphaeroides. Three iron-sulfur centers are also removed by this washing. Two of these are ferredoxin-like centers with electron paramagnetic resonance signals at g_v = 1.94 and midpoint potentials of +50 and ?250 mV at pH 7. The third is a high-potential iron-sulfur protein type signal centered at g 2.01 and a midpoint potential of +80 mV at pH 7. These centers have very similar properties to those of the well-characterized mammalian succinic dehydrogenase and account for the majority of iron-sulfur centers observed in chromatophores. Because it is so easily removed, it is concluded that succinic dehydrogenase is located on the outer surface of the chromatophore membrane, a conclusion supported by the fact that removal of the enzyme does not interfere with the kinetics of light-induced electron flow, nor does it allow cytochrome c₂ to escape from inside the chromatophore vesicles.     

Quality assurance of monoclonal products: Virologic and molecular biologic considerations

Summary The FDA has set limits concerning the viral and molecular contamination of monoclonal antibody products intended for human use. Industry has an obligation to be as familiar with these limits as it has been with federal requirements pertaining to pyrogens and bacteria. The assessment of risk from polynucleotides, based on molecular biologic and existing technical limitations, is discssed, as is the strategy of validating the purification of monoclonal antibodies of viral contaminants in terms of an indicator organism concept.     

Spectroscopic properties of the hydroxylase of methane monooxygenase

The hydroxylase component of methane monooxygenase (EC 1.14.13.25), which catalyzes the oxidation of methane to methanol, has been studied by visible, electron spin resonance and X-ray spectroscopies. The enzyme appears to possess a mu-oxo- or mu-hydroxo-bridged binuclear iron site, with no sulfur ligands to the cluster. Each Fe has 4-6 oxygen (or nitrogen) ligands, at an average distance of 1.92 +/- 0.03 A. The Fe-Fe distance is 3.05 +/- 0.05 A. Essentially all of the irons are in the Fe3+ state as the enzyme is prepared, but reduction with N-methylphenazonium methosulfate generates ESR-detectable states that appear to emanate from mixed-valence binuclear sites. One of these, with gav near 1.85, displays typical Curie law microwave saturation behavior, but the other, gav near 1.73, has a very potent method of spin-relaxation. Together they account for approximately 0.6 spins per molecule.     

The role of the Rieske iron-sulfur center as the electron donor to ferricytochrome c2 in Rhodopseudomonas sphaeroides

The Rieske iron-sulfur center in the photosynthetic bacterium Rhodopseudomonas sphaeroides appears to be the direct electron donor to ferricytochrome c₂, reducing the cytochrome on a submillisecond timescale which is slower than the rapid phase of cytochrome oxidation ($\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{3–5 μ}\text{s}$). The reduction of the ferricytochrome by the Rieske center is inhibited by 5-n-undecyl-6-hydroxy-4,7-dioxobenzothiazole (UHDBT) but not by antimycin. The slower (1–2 ms) antimycin-sensitive phase of ferricytochrome c₂ reduction, attributed to a specific ubiquinone-10 molecule (Q_z), and the associated carotenoid spectral response to membrane potential formation are also inhibited by UHDBT. Since the light-induced oxidation of the Rieske center is only observed in the presence of antimycin, it seems likely that the reduced form of Q_z (Q_zH₂) reduces the Rieske center in an antimycin-sensitive reaction. From the extent of the UHDBT-sensitive ferricytochrome c₂ reduction we estimate that there are 0.7 Rieske iron-sulfur centers per reaction center.UHDBT shifts the EPR derivative absorption spectrum of the Rieske center from g_y 1.90 to g_y 1.89, and shifts the E_m,7 from 280 to 350 mV. While this latter shift may account for the subsequent failure of the iron-sulfur center to reduce ferricytochrome c₂, it is not clear how this can explain the other effects of the inhibitor, such as the prevention of cytochrome b reduction and the elimination of the uptake of H⁺_II; these may reflect additional sites of action of the inhibitor.     

A microcosm for measuring survival and conjugation of genetically engineered bacteria in rhizosphere environments

A microcosm is described to evaluate and measure bacterial conjugation in the rhizosphere of barley and radish with strains ofPseudomonas cepacia. The purpose was to describe a standard method useful for evaluating the propensity of genetically engineered microorganisms (GEMs) to transfer DNA to recipient bacteria. Results demonstrated the formation of transconjugants from the rhizosphere of each plant 24 h after inoculation. Transconjugant populations peaked at 1.8 × 10² colony forming units (CFU)/g root and associated soil in barley and 2.0×10² CFU/g root and associated soil in radish; they then declined over the next five days of the experiment. No significant differences were found in the survival of transconjugant populations monitored from the two plant species. The microcosm was also used to document the formation of false positive transconjugants, which resulted from donor and recipientP. cepacia mating on the surface of selective agar plates instead of in microcosms. Transconjugants resulting from such plate mating occurred in substantial numbers during the first 5 days of the experiment but declined to undetectable numbers by day 7. The use of nalidixic acid was investigated to determine the magnitude of plate mating. The number of transconjugants detected from radish rhizosphere was reduced by two orders of magnitude by including nalidixic acid in the plating medium; this indicated that 99% of the transconjugants were a result of plate mating.     

Is the cognitive function of older patients affected by antihypertensive treatment? Results from 54 months of the Medical Research Council's trial of hypertension in older adults.

OBJECTIVE--To establish whether initiation of treatment with diuretic or beta blocker is associated over 54 months with change in cognitive function. DESIGN--A cognitive substudy, nested within a randomised, placebo controlled, single blind trial. SETTING--226 general practices from the Medical Research Council''s general practice research framework. SUBJECTS--A subset of 2584 subjects sequentially recruited from among the 4396 participants aged 65-74 in the trial of treatment of hypertension in older adults. The 4396 subjects were randomised to receive diuretic, beta blocker, or placebo. Subjects had mean systolic pressures of 160-209 mm Hg and mean diastolic pressures <115 mm Hg during an eight week run in. OUTCOME MEASURES--The rate of change in paired associate learning test (PALT) and trail making test part A (TMT) scores (administered at entry and at 1, 9, 21, and 54 months) over time. RESULTS--There was no difference in the mean learning test coefficients (rate of change of score over time) between the three treatments: diuretic -0.31 (95% confidence interval -0.23 to -0.39), beta blocker -0.33 (-0.25 to -0.41), placebo -0.30, (-0.24 to -0.36). There was also no difference in the mean trail making coefficients (rate of change in time taken to complete over time) between the three groups: diuretic -2.73 (95% confidence interval -3.57 to -1.88), beta blocker -2.08 (-3.29 to -0.87), placebo -3.01, (-3.69 to -2.32). A less conservative protocol analysis confirmed this negative finding. CONCLUSION--Treating moderate hypertension in older people is unlikely to influence, for better or for worse, subsequent cognitive function.