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Biomedical subjects

N Kaplan

Publications and source records attributed to N Kaplan.

At least 55 records · Page 3Linked to original sources
PubMed1988

Purification and characterization of the wild-type and mutant carboxy-terminal domains of the Escherichia coli Tar chemoreceptor.

The carboxy-terminal half of the Escherichia coli Tar chemoreceptor protein was cloned into an overproducing plasmid with the transcription of the insert under the control of the strong hybrid tac promoter. Two dominant mutations in the tar gene, which result in "tumble-only" (tar-526) or "swim-only" (tar-529) phenotypes and which are postulated to produce proteins locked in specific signalling modes, were introduced separately onto the overproducing plasmid. After induction with isopropyl-beta-D-thiogalactopyranoside, cells containing the plasmids produced about 10% of their soluble cellular protein as the carboxy-terminal fragments. A scheme to purify the overproduced fragments was developed. Typical yields of pure fragment were 5, 30, and 20 mg per liter of induced culture for the wild type, 526 mutant, and 529 mutant, respectively. Fast-protein liquid chromatography-gel filtration analysis of the pure fragments showed that they all existed as oligomers (ca. 103,000 daltons), possibly trimers or tetramers (monomer size is 31,000 daltons). However, the 529 mutant fragment showed an additional oligomeric form (240,000 daltons) corresponding approximately to an octamer. When chromatographed in the presence of 1% octylglucoside, all three fragments showed an identical single oligomeric size of about 135,000 daltons. Further differences between the fragments such as ion-exchange behavior and susceptibility to degradation were found. Taken together, these results suggest that conformational differences between the 529 mutant fragment and the other fragments exist and that these differences may correlate with the phenotypic effects of the tar-529 mutation.

Bacterial Proteins↗
PubMed1987

Reconstitution of emulsifying activity of Acinetobacter calcoaceticus BD4 emulsan by using pure polysaccharide and protein.

Acinetobacter calcoaceticus BD4 and BD413 produce extracellular emulsifying agents when grown on 2% ethanol medium. For emulsifying activity, both polysaccharide and protein fractions were required, as demonstrated by selective digestion of the polysaccharide with a specific bacteriophage-borne polysaccharide depolymerase, deproteinization of the extracellular emulsifying complex with hot phenol, and reconstitution of emulsifier activity with pure polysaccharide and a polysaccharide-free protein fraction. Chemical modification of the carboxyl groups in the polysaccharide resulted in a loss of activity. The protein required for reconstitution of emulsifying activity was purified sevenfold. The BD4 emulsan apparently derives its amphipathic properties from the association of an anionic hydrophilic polysaccharide with proteins.

Acinetobacter↗
PubMed1986

Magnetic resonance imaging of the pituitary gland.

Magnetic resonance imaging (MRI) was performed on 22 patients with a wide spectrum of pituitary disease and on 17 control subjects, in order to determine whether MRI is useful in localising and determining the extent of involvement of large and small pituitary tumours. The results indicate that MRI, with an 0.5 T superconducting magnet (Elscint, Israel), can be used to visualise large pituitary tumours and to determine the extent of parasellar and suprasellar involvement. The 'empty sella' syndrome can also be easily and confidently diagnosed. Some microadenomas can be visualised despite the relatively thick slices (0.7 cm) used in this study. These findings suggest that MRI in its current state of development is very useful in evaluating large pituitary lesions. With further technical refinements, improving the spatial resolution and decreasing slice thickness, this technique may come to be of some importance in the evaluation of pituitary microadenomas.

Acromegaly↗
PubMed1986

Anatomy of the normal knee as seen by magnetic resonance imaging.

Nuclear magnetic resonance imaging (MRI) was used to study the normal knee. As well as revealing bone quality, MRI provided useful information on intra-articular and extra-articular soft tissues. Midsagittal views gave clear images of the cruciate ligaments, and of the patellar and quadriceps tendons. Parasagittal views were the best for delineating the menisci which, like ligaments and tendons, are of low intensity; the semimembranosus tendon and its insertion to the proximal tibia were also seen clearly in these views. The cruciate ligaments and menisci, though visible in the coronal view also, were better seen in the sagittal view. Axial views provided information on the structure of the patella, its cartilage, the patellofemoral joint and posterior soft-tissue structures.

Adult↗
PubMed1985

Structural studies of the capsular polysaccharide of Acinetobacter calcoaceticus BD4.

Compositional analysis of the intact and carboxyl-reduced capsular polysaccharide of Acinetobacter calcoaceticus BD4 (PS-4) showed it to consist of L-rhamnose, D-glucose, D-glucuronic and D-mannose in molar ratios of 4:1:1:1. 13C-nuclear magnetic resonance spectroscopy, methylation analysis, oligosaccharide analysis and base-catalyzed beta-elimination were used to elucidate the primary structure. Oligosaccharides were obtained by enzymatic depolymerization with a specific bacteriophage-induced depolymerase and by partial acid hydrolysis. Form the results it is concluded that PS-4 consists of repeating units of the heptasaccharide (Formula: see text). The bacteriophage-induced depolymerase was found to be an endo-beta-D-glucosidase that hydrolyzed the bond beta-D-Glc-(1----3)-L-Rha to generate a heptasaccharide in 40% yield.

Acinetobacter↗
PubMed1985

The use of sample genealogies for studying a selectively neutral m-loci model with recombination.

A selectively neutral m-loci model with recombination is studied. A general method is developed to calculate the variance of the number of segregating sites in samples of arbitrary size and the m-loci homozygosity. The method is based on properties of the genealogy of the sample rather than diffusion approximations. To demonstrate the scope of the method several calculations are presented.

Genetic Variation↗
PubMed1985

Meniscal remodeling following partial meniscectomy--an experimental study in the dog.

The response of the meniscus to partial meniscectomy (in the avascular zone) was evaluated in 15 dogs. Following surgery 10 of the 15 dogs (67%) demonstrated a remodeling of the cut surface of the meniscus. This process appeared to begin with a fibrin clot which adhered to the meniscectomy surface. The organized clot was then populated by fibrocytes and eventually modulated into a fibrocartilage-like tissue by 12 weeks. The origin of the cells is unknown and may represent a migration of cells from the synovium, a proliferation of meniscal fibrochondrocytes, or both. The remodeling process appears to be associated with the presence of a fibrin clot, presumably from residual hemarthrosis. In those menisci that did not remodel [five of 15 (33%)], the meniscectomy surface remained relatively unchanged with no signs of progressive degeneration.

Animals↗
PubMed1985

Evolution and extinction of transposable elements in Mendelian populations.

A model of the evolution of a transposable element family in a Mendelian host population is proposed that incorporates heritable phenotypic mutations in the elements. The temporal behavior of the numbers of mutant and wild-type elements is studied, and the expected extinction time of the transposable element family is examined. Our results indicate that, if the mutant can be transposed equally well in the presence of the wild type, then it can be expected to be found in preponderance, whereas elements, such as retroviruses, where the transposing genome and its phenotypic expression are coupled, may be characterized by a low mutant frequency.

Animals↗
PubMed1984

Effects of atracurium on intraocular pressure.

The effects of atracurium on intraocular pressure (IOP) were compared with those of pancuronium in 20 patients less than 45 years-of-age requiring surgery for trauma of one eye. After a standard premedication and the application of topical analgesia to the upper airway, anaesthesia was induced with thiopentone i.v. and the trachea was intubated without the use of neuromuscular blockade. Following 20 min of steady state anaesthesia during which measurements of IOP, arterial pressure, heart rate, FIO2, FE'CO2 and CVP were recorded, one group of patients received atracurium 0.45 mg kg-1 and the other pancuronium 0.1 mg kg-1. The observations were repeated for a further 15 min before surgery commenced. Neither atracurium nor pancuronium produced any change in IOP. Atracurium was associated with greater cardiovascular stability than pancuronium.

Adolescent↗
PubMed1984

An analysis of the dynamics of mammalian mitochondrial DNA sequence evolution.

The dynamics of the substitution process for mammalian mitochondrial DNA have been modeled. The temporal behavior of several quantities has been studied and the model's predictions have been compared with estimates obtained from recent mtDNA sequence data for an increasingly divergent series of primates, the mouse and the cow (Anderson et al. 1981, 1982; Bibb et al. 1981; Brown et al. 1982). The results are consistent with the hypothesis that the decrease in the proportion of transitions observed as divergence increases is a consequence of the highly biased substitution process. In addition, the results support the hypothesis that, although a portion of the mtDNA molecule evolves at an extremely rapid rate, a significant portion of the molecule is under strong selective constraints.

Animals↗
PubMed1984

Non-operative treatment of severe injuries to the medial and anterior cruciate ligaments of the knee.

We are reporting the results of conservative treatment of concomitant injuries to the medial collateral and anterior cruciate ligaments of the knee in twenty-eight patients (average age, twenty-eight years), who were followed for an average of three years. Twenty patients had a good or excellent result. Eleven of the fifteen patients who played contact sports and six of the nine who played non-contact sports returned to their preinjury levels of athletic activity. The older and nonathletic individuals had the poorest final results. We concluded that in many individuals with combined injury to the medial collateral and anterior cruciate ligaments, the knee responds well when treated conservatively.

Adolescent↗
PubMed1982

Exopolysaccharide Distribution of and Bioemulsifier Production by Acinetobacter calcoaceticus BD4 and BD413.

The heavily encapsulated Acinetobacter calcoaceticus BD4 and the "miniencapsulated" single-step mutant A. calcoaceticus BD413 produced extracellular polysaccharides in addition to the capsular material. The molar ratio of rhamnose to glucose (3:1) in the extracellular BD413 polysaccharide fraction was similar to the composition of the capsular material. In both strains, the increase in capsular polysaccharide was parallel to cell growth and remained constant in stationary phase. The extracellular polysaccharides were detected starting from mid-logarithmic phase and continued to accumulate in the growth medium for 5 to 8 h after the onset of stationary phase. Strain BD413 produced one-fourth the total rhamnose exopolysaccharide per cell that strain BD4 did. Depending on the growth medium, 32 to 63% of the rhamnose polysaccharide produced by strain BD413 was extracellular, whereas in strain BD4 only 7 to 14% was extracellular. In all cases, strain BD413 produced more extracellular rhamnose polysaccharide than strain BD4 did. In glucose medium, strain BD413 also produced approximately 10 times more extracellular emulsifying activity than strain BD4 did. The isolated capsular polysaccharide obtained after shearing of BD4 cells showed no emulsifying activity. Thus, strain BD413 either produces a modified extracellular polysaccharide or excretes an additional substance(s) that is responsible for the emulsifying activity. Emulsions induced by the ammonium sulfate-precipitated BD413 extracellular emulsifier require the presence of magnesium ion and a mixture of an aliphatic and an aromatic hydrocarbon.

Journal Article↗