Bacteriopheophytin c in reaction center complexes of green photosynthetic bacteria

Two reaction center complexes prepared from cytoplasmic membranes of Chlorobium limicola f. thiosulfato-philum were compared by absorption and CD spectrophotometry. Bacteriopheophytin c (670 nm), which is optically active in one complex but not in the other, may serve as a secondary electron acceptor in the reaction center.     

Ontogeny of murine T lymphocytes: I. Maturation of thymocytes induced in vitro by tumor necrosis factor-positive serum (TNF+)

One question which is unresolved in developmental immunology is whether cortical thymocytes are the precursor cells which give rise to medullary thymocytes and peripheral T cells. Cortical thymocytes display a characteristic surface antigen phenotype (high TL and Thy-1, low H-2, no Qa-2, no Qa-3), are agglutinated by peanut agglutinin (PNA), and are unresponsive to concanavalin A (Con-A). The functionally more mature medullary thymocytes express a surface phenotype more closely resembling peripheral T cells (no TL, low Thy-1, high H-2, and some Qa-2), are not agglutinated by PNA, and are responsive to Con-A. An in vitro induction system has been devised in which mouse thymocytes undergo quantitative changes in surface antigens in less than 24 hr and increase their mitogen response to Con-A. The phenotypic changes are characterized by a decrease of TL and Thy-1 and an increase in H-2, Qa-2, and Qa-3. Studies in which thymocytes were fractionated on BSA gradients and by PNA agglutination demonstrate that the inducible cells have the properties of cortical thymocytes. Our data show that a subpopulation of cortical thymocytes can acquire phenotypic characteristics similar to medullary thymocytes and peripheral T cells.     

Purification and properties of the flavoenzyme D-lactate dehydrogenase from Megasphaera elsdenii.

A pyridine nucleotide independent D-lactate dehydrogenase has been purified to apparent homogeneity from the anaerobic bacterium Megasphaera elsdenii. The enzyme has a molecular weight of 105 000 by sedimentation equilibrium analysis with a subunit molecular weight of 55 000 by sodium dodecyl sulfate gel electrophoresis and is thus probably a dimer of identical subunits. It contains approximately 1 mol of FAD and 1 g-atom of Zn2+ per mol of protein subunit, and the flavin exhibits a fluorescence 1.7 times that of free FAD. An earlier purification [Brockman, H. L., & Wood, W. A. (1975 J. Bacteriol. 124, 1454--1461] results in substantial loss of the enzyme's zinc, which is required for catalytic activity. The new purification yields greater than 5 times the amount of enzyme previously isolated. The enzyme is specific for D-lactate, and no inhibition is observed with L-lactate. Surprisingly, the enzyme has a significant oxidase activity, which depends on the ionic strength. Vmax values of 190 and 530 min-1 were obtained at a gamma/2 of 0.224 and 0.442, respectively. Except for this atypically high oxygen reactivity, D-lactate dehydrogenase resembles other flavoenzyme dehydrogenases in that the flavin does not react with sulfite, the tryptophan content is low, and a neutral blue semiquinone is formed upon photochemical reduction. The enzyme flavin is reduced either by dithionite, by oxalate plus catalytic 5-deazaflavin in the presence of light, or by D-lactate. Two electrons per flavin were consumed in a dithionite titration, implyine with varying ratios of D-lactate and pyruvate, an Em7 of -0.219 +/- 0.007 V at 20 degrees C was calculated for the flavin. The enzyme requires dithiothreitol for stability. Rapid inactivation results when the enzyme is incubated with a substoichiometric level of Cu2+. This inactivation can be reversed by dithiothreitol. It is proposed that the enzyme possesses a pair of cysteine residues capable of facile disulfide formation.     

Eimeria tenella: specific reversal of t-butylaminoethanol toxicity for parasite and host by choline and dimethylaminoethanol.

t-Butylaminoethanol is an anticoccidial compound that is related structurally to the metabolically active substances, dimethylaminoethanol, and choline. Toxic effects of t-butylaminoethanol for chickens and Eimeria tenella are specifically overcome by feeding sufficient amounts of dimethylaminoethanol or choline. Dietary concentrations of the two above metabolites required to totally overcome toxic effiects of t-butylaminoethanol were determined and are expressed as the reversal ratio, inhibitor (t-butylamino-ethanol): metabolite. The inhibitor:choline ratio for total reversal of toxic effects of the inhibitor in chickens is approximately 1:10 over a concentration range of inhibitor from 0.019 to 0.05%. The inhibitor:choline ratio for reversal of antiparasitic effects is approximately 1:200 with a concentration of 0.01% inhibitor. The inhibitor:Dimethylaminoethanol ratio for reversal of toxic effects of the inhibitor in the chicken is approximately 1:7 with a concentration of 0.015% inhibitor. The inhibitor:dimethylaminoethanol ratio for reversal of antiparasitic effects is approxmately 1:20 wth a concentration of 0.01% inhibitor.     

A Simple Device for Staining Many Single-Hole Grids Without Individual Manipulation

In serial sectioning for electron microscopy one of the greatest problems encountered is that the Formvar support film may break when grids are being mounted in or removed from a holder used for staining, or during staining. The latter is particularly troublesome when grids are stained individually. We describe here a device that conveniently eliminates this problem.     

Determination of phenylalanine in serum using reversed-phase liquid chromatography and fluorescence detection

A liquid chromatography procedure is reported for determining phenylalanine in small volumes of serum. A 10-μl volume of serum was deproteinized with ethanol and an aliquot was derivatized with dansyl chloride reagent. The dansylated phenylalanine and the norleucine internal standard were separated using reversed-phase chromatography and measured with a fluorescence detector. Linearity was excellent over the range 50–800 mg/l. Within-run precision was better than 4%. Total analysis time including chromatography was approximately 40 min. As little as 300 pg of dansylated phenylalanine was detected.     

Enchanced accuracy of coliform testing in seawater by a modification of the most-probable-number method.

A 1-year study of marine water sample from six beach locations showed that the most-probable-number method failed to recover significant numbers of coli-forms. Modifying this method by transferring, after 48 h, presumptive negatives (growth and no gas production) to confirmed and fecal coliform media significantly improved recovery. Tests which were presumptive negative but confirmed as fecal coliform positive were designated as false negatives. Most-probable-number method false negatives occurred throughout the year, with 143 of 270 samples collected producing false negatives. More than 50% of fecal coliform false-negative isolates were Escherichia coli. Inclusion of false-negative tubes into the coliform most-probable-number method data resulted in increased violation of the California ocean water contact sports standard at all sites. More than 20% of the samples collected were in violation of this standard. These data indicate that modification of the most-probable-number method increases detection of coliform numbers in the marine environment.     

The zoospore ofOlpidium brassicae

Summary The ultrastructure of the zoospore ofOlpidium brassicae is described and compared with observations made of other zoospores of the uniflagellatePhycomycetes. The zoospore ofO. brassicae is characterized by an extensive, cone-shaped rhizoplast and a lack of a nuclear cap, as well as a side-body complex or a rumposome. Vacuoles which contain osmiophilic material are termed gamma-like particles. Three-dimensional reconstructions based on serial sectioning were made of the organelles in the region of the nucleus, showing that the zoospore ofO. brassicae contains one or at most two elaborately branched mitochondria. Microbodies have a high degree of interconnection and are in intimate association with the mitochondrion, lipid drops, and the nuclear envelope.