[Treatment of ischemic necrosis of femoral head by the transfer of vascular pedicled iliac periosteum]

OBJECTIVE

To investigate the therapeutical effect of treatment of ischemic necrosis of femoral head by the transfer of vascular pedicled iliac periosteum.

METHODS

From June 1983 to August 1997, 106 cases with ischemic necrosis of femoral head (II stage in 64 cases, III stage in 39 cases, IV stage in 3 cases) were treated by the transfer of vascular pedicled iliac periosteum with ascending branch of lateral femoral circumflex vessel or deep circumflex iliac vessel pedicle.

RESULTS

Followed up 2 years and 4 months to 16 years, there were excellent in 54 cases, better in 38 cases, moderate in 9 cases, poor in 5 cases, and 86.8% in excellent rate according to the criterion of the therapeutical effect on the repair and reconstruction of adult ischemic necrosis of femoral head.

CONCLUSION

Treating ischemic necrosis of femoral head by the transfer of vascular pedicled iliac periosteum has the advantage of constant pedicle, easily drawing materials and reliable therapeutical effect.

Tumor-derived EMMPRIN (extracellular matrix metalloproteinase inducer) stimulates collagenase transcription through MAPK p38

EMMPRIN (extracellular matrix metalloproteinase inducer) stimulates fibroblast metalloproteinases (MMP) 1, 2 and 3 (Kataoka et al. (1993) Cancer Res. 53, 3154-3158). Here we focus on MMP-1, showing that in lung tumors, MMP-1's cognate mRNA is strongly expressed in stromal fibroblasts adjacent to EMMPRIN-expressing tumor cells. In vitro, EMMPRIN upregulates MMP-1 mRNA expression in a concentration-dependent manner, with a peak accumulation at 24 h. The response is genistein-sensitive, suggesting it is dependent on tyrosine kinase activity. Analysis of tyrosine phosphorylation-dependent MAP kinases ERK 1/2, SAPK/JNK, and p38 showed that the activity of p38 but not that of the other 2 kinases was elevated in response to EMMPRIN. That p38 activity was required for EMMPRIN stimulation of MMP-1 was evident from results showing that the p38 inhibitor SB203580 blocked this response. This is the first available information regarding the mechanism by which tumor-associated molecules upregulate MMP synthesis in stromal fibroblasts.

Activation of NF-kappaB via a Src-dependent Ras-MAPK-pp90rsk pathway is required for Pseudomonas aeruginosa-induced mucin overproduction in epithelial cells

Cystic fibrosis (CF) is an autosomal recessive disorder, the most common lethal genetic disease in Caucasians. Respiratory disease is the major cause of morbidity and mortality. Indeed, 95% of CF patients die of respiratory failure. Pseudomonas aeruginosa, an opportunistic pathogen, chronically infects the lungs of over 85% of CF patients. It is ineradicable by antibiotics and responsible for airway mucus overproduction that contributes to airway obstruction and death. The molecular mechanisms underlying this pathology are unknown. Here we show that P. aeruginosa activates a c-Src-Ras-MEK1/2-MAPK-pp90rsk signaling pathway that leads to activation of nuclear factor NF-kappaB (p65/p50). Activated NF-kappaB binds to a kappaB site in the 5'-flanking region of the MUC2 gene and activates MUC2 mucin transcription. These studies bring new insight into bacterial-epithelial interactions and more specifically into the molecular pathogenesis of cystic fibrosis. Understanding these signaling and gene regulatory mechanisms opens up new therapeutic targets for cystic fibrosis.

Chemokine inhibition in rat stab wound brain injury using antisense oligodeoxynucleotides

Traumatic injury to the central nervous system (CNS) results in the breakdown of the blood-brain barrier and recruitment of hematogenous cells at the site of injury. The role of chemokines in this process has been well recognized and they have been regarded as promising targets for development of anti-inflammatory therapies. The expression of monocyte chemoattractant protein (MCP-1), in particular, has been closely linked to macrophage infiltration following trauma in rat brain. In this study we determined whether inhibition of MCP-1 following stab wound injury would reduce macrophage infiltration. Stab wound injured Sprague-Dawley rats were infused with MCP-1 sense or antisense oligonucleotides using an Alzet miniosmotic pump (1 microl/h for 3 days). Three days following injury, widespread gliosis was observed in both groups of rats as judged by glial fibrillary acidic protein (GFAP) immunoreactivity. Immunohistochemistry showed significantly less staining for MCP-1 in antisense treated animals. In addition, the number of macrophages were reduced by 30% in the antisense compared to the sense treated animals (P < 0.05). These results demonstrate that modulation of MCP-1 expression in stab wound injury directly affects monocytic infiltration and provide a basis for MCP-1 inhibition as a therapeutic strategy for controlling inflammatory events of traumatic brain injury.

Mucin gene (MUC 2 and MUC 5AC) upregulation by Gram-positive and Gram-negative bacteria

Bacterial infection of the lung is associated with mucin overproduction. In partial explanation of this phenomenon, we recently reported that supernatant from the Gram-negative organism Pseudomonas (P.) aeruginosa contained an activity that upregulated transcription of the MUC 2 mucin gene [J.-D. Li, A. Dohrman, M. Gallup, S. Miyata, J. Gum, Y. Kim, J. Nadel, A. Prince, C. Basbaum, Transcriptional activation of mucin by P. aeruginosa lipopolysaccharide in the pathogenesis of cystic fibrosis lung disease, Proc. Natl. Acad. Sci. U.S.A., 94 (1997) 967-972]. The purpose of the present study was to determine whether mucin genes other than MUC 2 are so regulated and whether Gram-positive organisms also contain mucin stimulatory activity. Results from in situ hybridization and RNase protection assays showed that P. aeruginosa upregulates MUC 5AC as well as MUC 2 in both bronchial explants and cultured airway epithelial cells. The upregulation of both genes by P. aeruginosa can be mimicked by lipopolysaccharide (LPS) and can be blocked by the tyrosine kinase inhibitor genistein. In addition, both genes are upregulated by a variety of Gram-positive as well as Gram-negative organisms showing the same rank order of potency. These data indicate the existence of a general mechanism by which epithelial cells respond to the presence of bacteria by increasing mucin synthesis.

Serum and egg yolk IgG antibody titers from laying chickens vaccinated with Pasteurella multocida

Through determining the serum and egg yolk antibody titers in immunized laying hens to Pasteurella multocida regularly, the growth-decline trend of the egg yolk antibody levels was found to be similar to that of the serum antibody levels (r = 0.94), but the growth and decline of the egg yolk antibody seemed to be delayed 3-6 days compared with that of the serum antibody, and the egg yolk antibody titers were generally lower than those of the serum antibody (P < 0.01). Serum and egg yolk antibody levels declined 3 and 6 days, respectively, after booster immunizations. The higher the antibody levels were before booster immunization, the more they declined.

Sp1 protein contributes to airway-specific rat MUC 2 mucin gene transcription

We have shown increases in the abundance of airway mucin mRNA during the pathogenesis of chronic obstructive pulmonary disease in rat models (Jany et al., 1991) and now seek to determine the underlying mechanisms. As transcriptional modulation may be involved, we provide here a functional analysis of the 5' flanking region of a rat mucin gene (MUC 2). Using deletion mutants to bp -859, we constructed expression cassettes in CAT vectors and transfected them into two MUC 2-expressing cell lines, SPOC 1, a rat airway epithelial cell line and IEC-6, a rat intestinal epithelial cell line, and into one MUC 2 non-expressing cell line, FR, a rat skin fibroblast cell line. Results indicated that nucleotides -59 to -40 mediated high level expression in SPOC 1, but not in the other cells. Used as a probe in gel shift assays, fragment -59/-40 formed complexes of differing mobilities when incubated with nuclear protein extracts from the three cell types. Mutation of the putative Sp1 binding site in the probe sequence interfered with protein binding in all three cell types, but anti-Sp1 antibody supershifted a band formed only by airway cell extracts. A model of airway cell-specific MUC 2 transcription is proposed.

Transcriptional activation of mucin by Pseudomonas aeruginosa lipopolysaccharide in the pathogenesis of cystic fibrosis lung disease

An unresolved question in cystic fibrosis (CF) research is how mutations of the CF transmembrane conductance regulator, a Cl ion channel, cause airway mucus obstruction leading to fatal lung disease. Recent evidence has linked the CF transmembrane conductance regulator mutation to the onset and persistence of Pseudomonas aeruginosa infection in the airways, and here we provide evidence directly linking P. aeruginosa infection to mucus overproduction. We show that P. aeruginosa lipopolysaccharide profoundly upregulates transcription of the mucin gene MUC 2 in epithelial cells via inducible enhancer elements and that this effect is blocked by the tyrosine kinase inhibitors genistein and tyr-phostin AG 126. These findings improve our understanding of CF pathogenesis and suggest that the attenuation of mucin production by lipopolysaccharide antagonists and tyrosine kinase inhibitors could reduce morbidity and mortality in this disease.

Transcriptional regulation of the lysozyme gene in airway gland serous cells

Lysozyme is expressed in serous, but not mucous, cells of the tracheobronchial glands and thereby constitutes a marker of the serous cell lineage in these glands. To identify DNA regulatory elements and transcription factors mediating the commitment of progenitor cells to the serous cell lineage, we have characterized the regulatory activity and DNA-protein interactions of the 5'-flanking region of the bovine lysozyme gene lys 5a. Results obtained from these studies indicate that although approximately 94 bp of 5'flanking DNA are necessary for high level expression in transient transfection assays, an evolutionarily conserved promoter within 66 bp of the transcription start site is sufficient to confer serous cell-specific expression. Farther upstream, within 6.1 kb of the 5' flanking region, are 4 silencers. Analysis of the serous cell-specific lysozyme promoter by electrophoretic mobility shift assay (EMSA) revealed the presence of binding sites for 3 serous cell nuclear proteins, designated LSF1, LSF2 and LSF3. Binding of LSF2 and LSF3 was localized to a 20-mer subdomain (-50/-30) of the cell-specific promoter using binding competition assays. More accurate identification of the protein binding site(s) was achieved through the use of mutagenesis, which implicated the motif 5' AAGGAAT 3' (-46/-40) in both protein binding and serous cell-specific transcriptional activity. This motif has previously been identified as a binding site for ets protein transcription factors, suggesting that serous cell-specific regulation of lys 5a transcription is partly controlled by the binding of ets-like protein(s) to the motif 5'AGGAAGT3'.

Systemic hypoxia dehydrates the space surrounding photoreceptors in the cat retina

PURPOSE

To assess the effects of systemic hypoxia and hyperoxia on the volume of the subretinal space (SRS).

METHODS

The authors measured the concentration of the extracellular space marker tetramethylammonium (TMA+) in the intact cat eye using double-barreled ion-selective microelectrodes. The retina was loaded with TMA+ by a single intravitreal injection. Systemic hypoxia was induced by adding nitrogen to the breathing mixture, and hyperoxia was induced by adding oxygen.

RESULTS

Hypoxia produced a slow increase in dark- adapted [TMA+]0, which was prominent in amplitude in the distal portion of the retina, suggesting a shrinkage of the SRS. This effect was essentially proportional to the decrease in arterial oxygen tension (PaO2) below the normoxic level. Dark-adapted (TMA+)0 began to increase at a PaO2 of 60 to 80 mm Hg and was enhanced by 13% to 15% at a PaO2 of 40 mm Hg. Because of its slow onset, the size of the increase also was related to the duration of hypoxia. The light-evoked decrease in (TMA+)0 in the SRS was larger in amplitude during hypoxia than in normoxia. This difference increased with severity of hypoxia, beginning at approximately the same PaO2 as the increase in dark-adapted (TMA+)0. Interestingly, the hypoxic increase in amplitude depended on light intensity, i.e., it was proportionally greater at lower intensities versus higher ones. Background illumination suppressed the hypoxia-induced increase in (TMA+)0 in SRS, inhibiting it by approximately 50% at levels of hypoxia down to a PaO2 of 40 mm Hg. Systemic hyperoxia produced the reverse effect of hypoxia. Between two extreme states, e.g., illumination during hyperoxia (PaO2 > 200 mm Hg) versus severe hypoxia in darkness (PaO2 approximately 40 mm Hg), extracellular volume may change more than 4-fold.

CONCLUSIONS

The observations of this study indicate that the space surrounding photoreceptors shrinks in response to hypoxia. This shrinkage should affect concentrations of all ions and metabolites located in the subretinal space.

Surgical management of the hypopharyngeal and cervical esophageal cancer

Between December 1979 and December 1992, 15 patients with hypopharyngeal and cervical esophageal cancer were treated surgically. Total pharyngolaryngectomy and partial cervical esophagectomy were performed and the defects were reconstructed with cervical skin flaps in 2 cases. The free jejunal segments were used in 6 cases following total pharyngolaryngectomy and cervical esophagectomy, cervical esophagectomy (larynx preserved) was repaired with free jejunal graft in 1 case. The pharyngogastric anastomosis following total pharyngolaryngoesophagectomy were performed in 4 cases, one of them, used pectoralis major myocutaneous flap for resection of soft tissue and skin of the neck. The pectoralis major myocutaneous flap and forearm free flap in 1 case respectively were used to reconstruct the deficits of total laryngectomy and partial pharyngectomy, and partial pharyngolaryngectomy. In our series, 1, 3, 5 years survival rates were 73.3% (11/15), 50% (6/12) and 55.6% (5/9), respectively. The advantages and disadvantages of a variety of operative procedures and the cervical lymph nodes management will be discussed.

Light-dependent hydration of the space surrounding photoreceptors in the cat retina

We have studied the effect of retinal illumination on the concentration of the extracellular space marker tetramethylammonium (TMA+) in the dark-adapted cat retina using double-barreled ion-selective microelectrodes. The retina was loaded with TMA+ by a single intravitreal injection. Retinal illumination produced a slow decrease in [TMA+]o, which was maximal in amplitude in the most distal portion of the space surrounding photoreceptors, the subretinal space. The light-evoked decrease in [TMA+]o was considerably slower and of a different overall time course than the light-evoked decrease in [K+]o, also recorded in the subretinal space. [TMA+]o decreased to a peak at 38 s after the onset of illumination, then slowly recovered towards the baseline, and transiently increased following the offset of illumination. It resembled the light-evoked [TMA+]o decreases previously recorded in the in vitro preparations of frog (Huang & Karwoski, 1990, 1992) and chick (Li et al., 1992, 1994) but was considerably larger in amplitude, 22% compared with 7%. As in frog, where it was first recorded, the light-evoked [TMA+]o decrease is considered to originate from a light-evoked increase in the volume of the subretinal space (or subretinal hydration). A mathematical model accounting for [TMA+]o diffusion predicted that the volume increase underlying the response was 63% on average and could be as large as 95% and last for minutes. The estimated volume increase was then used to examine its effect on K+ concentration in the subretinal space. We conclude that a light-dependent hydration of the subretinal space represents a significant physiological event in the intact cat eye, which should affect the organization of the interphotoreceptor matrix, and the concentrations of all ions and metabolites located in the subretinal space.

Calcium gradients and light-evoked calcium changes outside rods in the intact cat retina

We have studied light-evoked changes in extracellular Ca2+ concentration ([Ca2+]o) in the intact cat eye using ion-sensitive double-barreled microelectrodes. Two prominent changes in Ca2+ concentration were observed that differed in retinal location. There was a light-evoked increase in [Ca2+]o, accompanied by brief ON and OFF transients, which was maximal in the inner plexiform layer and was not further studied. There was an unexpected sustained light-evoked decrease in [Ca2+]o, of relatively rapid onset and offset, which was maximal in the distalmost region of the subretinal space (SRS). [Ca2+]o in the SRS was 1.0 mM higher than in the vitreous humor during dark adaptation and this transretinal gradient disappeared during rod-saturating illumination. After correcting for the light-evoked increase in the volume of the SRS, an increase in the total Ca2+ content of the SRS during illumination was revealed, which presumably represents the Ca2+ released by rods. To explain the light-evoked [Ca2+]o changes, we used the diffusion model described in the accompanying paper (Li et al., 1994b), with the addition of light-dependent sources of Ca2+ at the retina/retinal pigment epithelium (RPE) border and rod outer segments. We conclude that a drop in [Ca2+]o around photoreceptors, which persists during illumination and reduces a transretinal Ca2+ gradient, is the combined effect of the light-evoked SRS volume increase, Ca2+ release from photoreceptors, and an unidentified mechanism(s), which is presumably Ca2+ transport by the RPE. The relatively rapid onset and offset of the [Ca2+]o decrease remains unexplained. These steady-state shifts in [Ca2+]o should have significant effects on photoreceptor function, especially adaptation.

Light-dependent hydration of the space surrounding photoreceptors in chick retina

PURPOSE

To characterize the light-evoked increase in the volume (or hydration) of the subretinal space (SRS) of chick retina and to investigate its retinal pigment epithelial (RPE) origin.

METHODS

The authors perfused chick retina-RPE-choroid preparations with the extracellular space marker, tetramethylammonium (TMA+), and estimated its concentration ([TMA+]o) using double-barreled, ion-selective electrodes. They recorded dark-light changes in subretinal [TMA+]o and studied the effects of drugs that suppress RPE ion transport and conductances.

RESULTS

The authors observed a slow, light-evoked decrease in subretinal [TMA+]o, about 7% in amplitude, that slowly returned to baseline and then increased at light OFF. It was 40% to 65% inhibited by bumetanide and furosemide, known to inhibit RPE apical membrane Na-K-Cl cotransport; 70% to 80% inhibited by DIDS, an inhibitor of RPE basal membrane chloride conductance, and 50% inhibited by 0.5 mM BaCl2, a blocker of the K+ conductance of the RPE apical membrane. Decreases in subretinal [TMA+]o also were produced when the authors lowered [Cl-]o or [K+]o in the SRS by reducing concentrations in the retinal perfusate. The effect on [TMA]o was larger for [Cl-]o than for [K+]o and was inhibited by bumetanide and DIDS.

CONCLUSIONS

Changes in subretinal ion concentrations in light and darkness, most likely [K+]o, modify SRS hydration by modulating RPE apical membrane Na-K-Cl cotransport, as well as the conductive effluxes of K+ across the apical membrane and Cl- across the basal membrane. These changes depend principally on the movement of water into or out of the RPE. In turn, subretinal hydration modifies local ion concentrations and the composition of the interphotoreceptor matrix.

Mathematical model of TMA+ diffusion and prediction of light-dependent subretinal hydration in chick retina

PURPOSE

To derive a mathematical model of TMA+ diffusion across the retina that can be used to estimate the amplitude and kinetics of the light-evoked increase in subretinal hydration and its effect on the concentration of other ions.

METHODS

All experimental data were obtained in chick retina-pigment epithelium-choroid preparations as described in the accompanying paper.

RESULTS

Diffusional properties of the retina were derived from the time course of [TMA+]o in the subretinal space (SRS) after changes in the retinal perfusate. Then, the SRS volume changes underlying the light-induced [TMA+]o response can be derived using a mathematical model of TMA+ diffusion. Complete retinal depth series of light-evoked [TMA+]o responses could be simulated by producing a corresponding expansion of the SRS. Volume changes inferred from the diffusion model were 2.2 to 3.8 times larger and more prolonged than could be derived directly from delta [TMA+]o. The model predicted up to a 20% peak increase in subretinal-space hydration during illumination. The effects of this volume increase on subretinal K+ and Ca2+ were estimated. These predictions were supported by inhibiting the volume increase with DIDS, which blocks retinal pigment epithelium basal membrane Cl- conductance.

CONCLUSIONS

The primary source of light-evoked changes in extracellular TMA+ concentration recorded throughout the retina is an increase in hydration (volume) of the subretinal space. The response spreads to the inner retina by diffusion. Effects of TMA+ diffusion lead to large underestimates of the underlying volume changes. The light-evoked volume change alters the composition of the subretinal space and light-induced responses of other ions.

[Anti-inflammatory effect of Caragana microphylla Lam]

Caragana microphylla can antagonize the inflammation induced by carrageenin, hot water and croton oil. It can also inhibit the proliferation of granuloma, blood capillary permeability, phagocytic function of mononuclear phagocyte system, and synthesis or release of PGE2 at the inflamed part.

Crystal structure of insecticidal delta-endotoxin from Bacillus thuringiensis at 2.5 A resolution

The structure of the delta-endotoxin from Bacillus thuringiensis subsp. tenebrionis that is specifically toxic to Coleoptera insects (beetle toxin) has been determined at 2.5 A resolution. It comprises three domains which are, from the N- to C-termini, a seven-helix bundle, a three-sheet domain, and a beta sandwich. The core of the molecule encompassing all the domain interfaces is built from conserved sequence segments of the active delta-endotoxins. Therefore the structure represents the general fold of this family of insecticidal proteins. The bundle of long, hydrophobic and amphipathic helices is equipped for pore formation in the insect membrane, and regions of the three-sheet domain are probably responsible for receptor binding.

Dark adaptation of horizontal cells in the teleost fish retina

The dark adaptation behaviors of rod-driven and cone-driven horizontal cells were examined by analyzing their light responses recorded intracellularly in the intact, immobilized carp, and compared with that of the electroretinographic b-wave recorded simultaneously. Like the b-wave, the light responsiveness of rod horizontal cells increased gradually with time in the dark and attained a steady level at 60 min. On the other hand, cone horizontal cells initially increased in light responsiveness in the first 10 min, but thereafter decreased steadily so that the response amplitudes of these cells to bright light flashes were only 3-5 mV. The results suggest that cone horizontal cells are strongly suppressed in prolonged darkness.

Electroretinographic b-wave merely reflects the activity of the rod system in the dark-adapted carp retina

The electroretinogram and responses of intermediate horizontal cells (IHCs) were recorded simultaneously and studied under dark-adapted conditions in intact crucian carp, with the hope of providing an answer to the controversy whether the scotopic b-wave contains contribution from both rods and cones. Our observations indicate that the dark-adapted b-wave follows the univariance principle perfectly in that: (1) b-wave forms and shapes of response amplitude vs light intensity relationships did not depend on the stimulus wavelength; (2) response amplitudes to flashes of mixed wavelengths agreed exactly with the values predicted in accordance with the univariance principle. Furthermore, the spectral sensitivity of the b-wave matched well that of the IHC, receiving input exclusively from rods. In consequence, we conclude that the dark-adapted b-wave merely reflects the activity of the rod system, and the discrepancy between the spectral sensitivities of the b-wave and IHC response compared with the absorption spectrum of the rod photopigment may be due to the self-screening effect caused by the high optical density of porphyropsin in situ.

[A pattern-ERG study of amblyopia]

26 normal and 60 amblyopic children were examined with the P-ERG. The results showed that P-ERG in amblyopes was significantly abnormal, with delay in the latent periods of wave b and the after potential, as well as reduction in the amplitudes of the same. The latency of wave a was also delayed in some severe amblyopes. The abnormal manifestations of P-ERG and the mechanism in their occurrence were discussed. The P-ERG could be a sensitive and objective diagnostic method for amblyopia.

[Studies on stimulating circulation to end stasis in scleroderma]

Of 725 cases of scleroderma, 265 were of systemic type (the sex ratio being 1M:6F) and 460 of circumscribed type (the sex ratio being 1M:9F). The patients were divided into three groups and treated with three different stimulating circulation to end stasis (SCES) prescriptions. Satisfactory therapeutic effects were obtained in all. According to the clinical practice and laboratory findings, although SCES therapy exerted manifold actions on the disease, it not only softened the indurated connective tissues, tonified the body and improved the symptoms, but also improved laboratory indexes as follows: nailfold bed capillary, parameter of the peripheral blood stream in patients, content of urinary 2-ketol, 17-KS, free corten, serum joint-hexose, amino-hexose and histopathology including ultrastructure of the skin. The main effect was the improvement of circulation, especially the microcirculation and regulation of the metabolism of the connective tissues. Great attention should be paid to the drug's function of softening the indurated connected tissues. For further investigation, the authors have stressed three important points: screening of clinical symptoms and signs, examination of blood circulatory disturbances, and examination of pathological changes of the connective tissue. The necessity of developing new criteria for judging the therapeutic effects was emphasized.

Ammonia switch-off of nitrogenase from Rhodobacter sphaeroides and Methylosinus trichosporium: no evidence for Fe protein modification

In vivo switch-off of nitrogenase activity by NH4+ is a reversible process in Rhodobacter sphaeroides and Methylosinus trichosporium OB3b. The same pattern of switch-off in Rhodospirillum rubrum is explained by ADP-ribosylation of one of the Fe protein subunits, however, no evidence of covalent modification could be found in the subunits from either R. sphaeroides or M. trichosporium. Fe protein subunits from these organisms showed no variant behaviour on SDS-PAGE, nor were they 32P-labeled following switch-off. These observations suggest either that the attachment of the modifying group to the Fe protein in these organisms is quite labile and does not survive in vitro manipulation, or that the mechanism of switch-off is different than that seen in Rhodospirillum.

Changes in amino acid and nucleotide pools of Rhodospirillum rubrum during switch-off of nitrogenase activity initiated by NH4+ or darkness

Amino acid and nucleotide pools were measured in nitrogenase-containing Rhodospirillum rubrum cultures during NH4+- or dark-induced inactivation (switch-off) of the Fe protein. A big increase in the glutamine pool size preceded NH4+ switch-off of nitrogenase activity, but the glutamine pool remained unchanged during dark switch-off. Furthermore, methionine sulfoximine had no effect on the rate of dark switch-off, suggesting that glutamine plays no role in this process. In the absence of NH4+ azaserine, an inhibitor of glutamate synthate, raised glutamine pool levels sufficiently to initiate switch-off in vivo. While added NH4+ substantially increased the size of the nucleotide pools in N-limited cells, the kinetics of nucleotide synthesis were all similar and followed (rather than preceded) Fe protein inactivation. Darkness had little effect on nucleotide pool sizes. Glutamate pool sizes were also found to be important in NH4+ switch-off because of the role of this molecule as a glutamine precursor. Much of the diversity reported in the observations on NH4+ switch-off appears to be due to variations in glutamate pool sizes prior to the NH4+ shock. The nitrogen nutritional background is an important factor in determining whether darkness initiates nitrogenase switch-off; however, no link has yet been established between this and NH4+ (glutamine) switch-off.

Preliminary crystallographic studies on bacterioferritin from Azotobacter vinelandii

Bacterioferritin-cytochrome from Azotobacter vinelandii is an unusual protein containing haem groups as well as iron core like other ferritin. This paper reports the purification of bacterioferritin by affinity chromatography and the formation of brick-red crystals from a solution containing MgCl2. The crystals are optical isotropic with maximum dimensions of 0.4 X 0.4 X 0.1 mm3. The preliminary X-ray crystallographic studies have been performed. 1.5 degrees unscreened precession photographs show that the crystals of bacterioferritin belong to the cubic system, space group I432, with cell dimension 230 A. There are probably 8 molecules in one cubic unit cell and the molecule might have 32 symmetry. A molecular diameter of 115 A is derived from the packing of the molecules and a molecular weight of 826,000 is estimated for bacterioferritin.

Presence of a cytochrome b-containing ferritin in Azotobacter vinelandii

It has been demonstrated that a cytochrome b-containing ferritin is present in Azotobacter vinelandii. After DEAE cellulose chromatography and purification fractional precipitation by 50% of the saturated ammonium sulfate of the extract prepared from A. vinelandii cells, a hexagonal crystalline preparation is obtained. The protein contains 4--6% of nonheme iron. The protein molecule is made up of an electron dense iron core with a diameter of 70A and a protein shell with a diameter of 120A. The Fe core can be removed from the shell by the treatment with chelating and reducing agents. Electron micrographs and absorption spectra reveal that the protein shells are very similar before and after the removal of the core. The electrophoretic mobility and immunological properties of the Fe-free protein against the antibody of ferritin are very similar to those of the protein before the removal of the iron. From the above characteristics, it can be inferred that the protein belongs to ferritin. The protein part contains protoheme as prosthetic group and so it belongs to cytochrome b. Hence, the protein prepared from A. vinelandii is a kind of cytochrome b-containing ferritins. The possible role of the ferritin in biological nitrogen fixation is discussed in this paper.