The p lambda CM system: phage immunity-specific incompatibility with IncP-1 plasmids

Summary A pCM2 replicon derived by an N^– deletion from ::Tn9 which carries the imm434 immunity region is incompatible with some (but not all) IncP-1 plasmids. The imm pCM1 replicon does not show the same incompatibility behavior.     

黄素氧还蛋白参与的固氮链电子传递

棕色固氮菌中电子载体Fld直接向固氮酶铁蛋白传递电子。Fld_(ox)至Fld_R是双电子二步还原反应,极谱半波电位分别为-210、-550 mV。Fld_(ox)至Fld_(SR)的中点电位为-280 mV,Fld_(SR)至Fld_R为-500mV。铁蛋白中点电位为-256mV,加MgATP后为-390 mV。Fld_R与铁蛋白ox组成的电池电动势为244mV,电子传递可自发进行,反应的J△G~o为-23KJ/摩尔,铁蛋白被Fld_R还原的K_a=1.3×120~4,加入MgATP后△G~o为-10.6KJ/摩尔,K_a=72。因此,未加入MgATP时电子传递反应更易进行。     

Assimilation of 13NH 4 + by Anthoceros grown with and without symbiotic Nostoc

The pathways of assimilation of ammonium by pure cultures of symbiont-free Anthoceros punctatus L. and the reconstituted Anthoceros-Nostoc symbiotic association were determined from time-course (5–300 s) and inhibitor experiments using ¹³NH ₄ ⁺ . The major product of assimilation after all incubation times was glutamine, whether the tissues were cultured with excess ammonium or no combined nitrogen. The ¹³N in glutamine was predominantly in the amide-nitrogen position. Formation of glutamine and glutamate by Anthoceros-Nostoc was strongly inhibited by either 1mM methionine sulfoximine (MSX) or 1 mM exogenous ammonium. These data are consistent with the assimilation of ¹³NH ₄ ⁺ and formation of glutamate by the glutamine synthetase (EC 6.3.1.2)-glutamate synthase (EC 1.4.7.1) pathway in dinitrogen-grown Anthoceros-Nostoc. However, in symbiont-free Anthoceros, grown with 2.5 mM ammonium, formation of glutamine, but not glutamate, was decreased by either MSX or exogenous ammonium. These results indicate that during short incubation times ammonium is assimilated in nitrogenreplete Anthoceros by the activities of both glutamine synthetase and glutamate dehydrogenase (EC 1.4.1.2). In-vitro activities of glutamine synthetase were similar in nitrogen-replete Anthoceros and Anthoceros-Nostoc, indicating that the differences in the routes of glutamate formation were not based upon regulation of synthesis of the initial enzyme of the glutamine synthetase-glutamate synthase pathway. When symbiont-free Anthoceros was cultured for 2 d in the absence of combined nitrogen, total ¹³NH ₄ ⁺ assimilation, and glutamine and glutamate formation in the presence of inhibitors, were similar to dinitrogen-grown Anthoceros-Nostoc. The routes of immediate (within 2 min) glutamate formation and ammonium assimilation in Anthoceros were apparently determined by the intracellular levels of ammonium; at low levels the glutamine synthetase-glutamate synthase pathway was predominant, while at high levels independent activities of both glutamine synthetase and glutamate dehydrogenase were expressed.     

Preliminary crystallographic studies of lobster D-glyceraldehyde-3-phosphate dehydrogenase and the modified enzyme carrying the fluorescent derivative

When the active-site carboxymethylated D-glyceraldehyde-3-phosphate dehydrogenase is irradiated with ultraviolet light in the presence of NAD+, a fluorescent NAD derivative that is covalently linked to the enzyme is obtained. A preliminary crystallographic study of this fluorescent derivative, as well as of the native and the carboxymethylated enzymes from Palinurus versicolor, showed that they are isomorphous and belong to space group C2 as reported for the native enzyme from Palinurus vulgaris. The three forms of the enzyme, although they have identical unit cell parameters, differ considerably in their diffraction patterns, indicating marked differences in conformation in spite of the fact that they differ chemically only in a restricted region around the active site.     

Effects of high-frequency oscillatory ventilation on vagal and phrenic nerve activities

This study was undertaken to define the mechanism for the respiratory inhibition observed during high-frequency oscillatory ventilation (HFOV). The effects of HFOV on the activities of single units in the vagus (Vna) and phrenic nerves (Pna) were examined in pentobarbital-anesthetized dogs. The animals were either ventilated by intermittent positive-pressure ventilation (IPPV) with and without positive end-expiratory pressure (PEEP), or by HFOV at a frequency of 25 Hz and pump displacement volume of 3 ml/kg. In 13 vagal units the Vna was much higher during HFOV than during IPPV or airway occlusion at a matched airway pressure. Ten units in the phrenic nerves were examined, and Pna (expressed as bursts/min) was attenuated by HFOV in all of them. In four of them, the effect of cooling the vagi to 8-10 degrees C on Pna was examined, and it was found that HFOV failed to alter the Pna. We conclude that 1) HFOV stimulates the pulmonary vagal afferent fibers continuously and to a degree greater than that due to static lung inflation and increased airway pressure and 2) the increased vagal activity during HFOV probably causes phrenic nerve activity inhibition.     

Unique acceptors for poly(ADP-ribose) in resting,proliferating and DNA-damaged human lymphocytes

Acceptor proteins for poly(adenosine diphosphoribosyl)ation were determined in resting human lymphocytes, in lymphocytes with N-methyl-N′-nitro-N-nitrosoguanidine-induced DNA damage and in lymphocytes stimulated to proliferate by phytohemagglutinin. Kinetic studies showed that the increase in ADP-ribosylation which occurred in response to N-methyl-N′-nitro-N-nitrosoguanidine (MNNG) treatment was greater in magnitude but more transient in duration than that which occurred in phytohemagglutinin-stimulated cells. Gel electrophoretic analyses revealed that MNNG treatment and phytohemagglutinin stimulation both caused an increase in ADP-ribosylation of poly(ADP-ribose) polymerase and core histones. In MNNG-treated cells, an increase in ADP-ribosylation of histone H1 was also observed. In contrast, phytohemagglutinin-stimulated cells showed no increase in ADP-ribosylation of histone H1. In MNNG-treated cells there was also ADP-ribosylation of a protein of molecular weight 62 000, while in phytohemagglutinin-stimulated cells there was a marked increase in ADP-ribosylation of a protein of molecular weight 96000. MNNG treatment of phytohemagglutinin-stimulated cells produced a pattern of ADP-ribosylation that appeared to be due to the combined effects of the individual treatments. 3-Aminobenzamide effectively inhibited ADP-ribosylation under all treatment conditions.     

Stimulation of Mycelial Growth of Endothia parasitica by Heavy Metals

Of 16 metal cations tested on agar medium, only copper and iron stimulated mycelial growth of Endothia parasitica in relatively high concentrations. Similarly enhanced growth was produced in high (32%) glucose concentrations and also when the fungus was grown on cellophane placed over the agar surface. E. parasitica secreted large amounts of oxalate that precipitated primarily as calcium oxalate at the periphery of the fungal colony, causing an opaque halo in the medium. Mycelial growth was retarded greatly when calcium oxalate accumulated, but retardation was reversed by copper and iron salts that prevented accumulation of the calcium oxalate crystals. E. parasitica grew well on media containing copper oxalate and copper-calcium oxalate but grew poorly with calcium oxalate as the carbon source and was inhibited by sodium oxalate in the medium. The specificity by which only copper and iron salts stimulated mycelial growth suggested that the metal and oxalate ions interact to form specific oxalate complexes that reverse the inhibition of simple oxalate salts. This probably accounts for enhanced growth in the presence of otherwise toxic levels of metals and oxalate. The stimulation did not occur in liquid cultures.     

Activity of phenol oxidases at the puparium formation stage in development of nineteen lozenge mutants of Drosophila melanogaster

Phenol oxidase activity of activated A₁ and A₂ (A₃) electrophoretic components from 19 lozenge mutant and three lozenge double mutant strains was compared to that of wild type flies. Melanin production by the activated A components with tyrosine as substrate was compared to activity in the same acrylamide gels with dopa as substrate. Melanin production decreased, first in the A₁ band and then in the A₂ (A₃) band, with increased morphological expression of the mutant genes. No melanin bands were obtained with either substrate in five of the more severely affected mutants. A possible correlation between phenol oxidase activity and quinone production necessary for normal development of eyes, female accessory sex organs, and claws is discussed.Supported by PHS grant AM-08331-05.     

CHROMOSOME MICROMANIPULATION : III. Spindle Fiber Tension and the Reorientation of Mal-Oriented Chromosomes

Kinetochore reorientation is the critical process ensuring normal chromosome distribution. Reorientation has been studied in living grasshopper spermatocytes, in which bivalents with both chromosomes oriented to the same pole (unipolar orientation) occur but are unstable: sooner or later one chromosome reorients, the stable, bipolar orientation results, and normal anaphase segregation to opposite poles follows. One possible source of stability in bipolar orientations is the normal spindle forces toward opposite poles, which slightly stretch the bivalent. This tension is lacking in unipolar orientations because all the chromosomal spindle fibers and spindle forces are directed toward one pole. The possible role of tension has been tested directly by micromanipulation of bivalents in unipolar orientation to artificially create the missing tension. Without exception, such bivalents never reorient before the tension is released; a total time "under tension" of over 5 hr has been accumulated in experiments on eight bivalents in eight cells. In control experiments these same bivalents reoriented from a unipolar orientation within 16 min, on the average, in the absence of tension. Controlled reorientation and chromosome segregation can be explained from the results of these and related experiments.