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Biomedical subjects

R Kahn

Publications and source records attributed to R Kahn.

At least 19 recordsLinked to original sources
PubMed1992

Bacterial expression, purification, and in vitro N-myristoylation of HIV-1 p17gag.

The coding region of the N-terminal 17-kDa portion of HIV-1 Pr55gag (p17gag) was cloned into the pET-3c expression vector and was used to overexpress HIV-1 p17gag in Escherichia coli. Induction of the transformed bacteria caused the accumulation of a 17-kDa polypeptide in the soluble cell fraction which was released by sonication in hypotonic nondetergent buffer. The 17-kDa polypeptide was purified by ammonium sulfate precipitation and successive chromatography on G-75 Sephadex, DEAE-Sephacel, and S-Sephadex. The final product was purified 12-fold with about a 16% recovery from the original soluble cell lysate and was judged to be 97+% pure by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Western blotting with two different antibodies confirmed the identify of the purified 17-kDa polypeptide as authentic p17gag. In the presence of myristoyl-CoA and bovine brain N-myristoyl-transferase, p17gag was quantitatively N-myristoylated in vitro with a pseudo-first-order rate constant of 4.7 +/- 1.0 x 10(-3) min-1, but with only about 3% of the catalytic efficiency of N-myristoylation of a 16-residue peptide homologous to the N-terminus of p17gag. The myristate group in the N-myristoylated p17gag was stable to treatment with detergent and hydroxylamine consistent with a covalent N-acyl-amide linkage. The N-myristoylglycyl linkage was confirmed by partial acid hydrolysis and identification of the p-nitrobenzylazlactone derivative of the resulting N-myristoylglycine by high-performance liquid chromatography.

Escherichia coli↗
PubMed1991

Structure of the calcium-dependent lectin domain from a rat mannose-binding protein determined by MAD phasing.

Calcium-dependent (C-type) animal lectins participate in many cell surface recognition events mediated by protein-carbohydrate interactions. The C-type lectin family includes cell adhesion molecules, endocytic receptors, and extracellular matrix proteins. Mammalian mannose-binding proteins are C-type lectins that function in antibody-independent host defense against pathogens. The crystal structure of the carbohydrate-recognition domain of a rat mannose-binding protein, determined as the holmium-substituted complex by multiwavelength anomalous dispersion (MAD) phasing, reveals an unusual fold consisting of two distinct regions, one of which contains extensive nonregular secondary structure stabilized by two holmium ions. The structure explains the conservation of 32 residues in all C-type carbohydrate-recognition domains, suggesting that the fold seen here is common to these domains. The strong anomalous scattering observed at the Ho LIII edge demonstrates that traditional heavy atom complexes will be generally amenable to the MAD phasing method.

Acute-Phase Proteins↗
PubMed1991

Crystallization and crystal packing of Proteus mirabilis PR catalase.

The tetrameric catalase from Proteus mirabilis PR (EC 1.11.1.6), known to bind NADPH, has been crystallized by the hanging-drop method in a form apparently depleted in dinucleotide. The crystals belong to the hexagonal space group P6(2)22 with a = b = 111.7 A, c = 248.8 A. There is one subunit in the asymmetric unit. Data were collected to 2.9 A at the L.U.R.E. (Orsay) synchrotron radiation facility. The tetramers have been located in the crystal, centered on the site (1/2, 0, 0) with 222 symmetry.

Catalase↗
PubMed1991

Desipramine treatment in panic disorder.

Apart from imipramine (IMI), the efficacy of tricyclic antidepressants in panic disorder (PD) has received surprisingly little investigation. The authors report on a 6 week open trial of desipramine (DMI) preceded by a 10 day placebo lead-in, in 15 patients with PD. By week 6, 80% of the patients were globally rated as much or very much improved on a mean dose of 198 mg. Much of the improvement resulted from a reduction in non-panic attack symptomatology (i.e., psychic, somatic and phobic anxiety). Longer duration of illness, male gender and residual psychic anxiety were associated with poorer response in a subgroup of patients. DMI caused minimal intolerable side effects, suggesting possible compliance advantages in comparison to IMI. Beyond supporting the efficacy of DMI in PD, the results of the study point to a significant medication responsive non-panic illness component and caution against over-relying on panic attacks in assessing both illness severity and treatment response.

Adult↗
PubMed1990

Anemia in general practice.

Among 4928 consecutive consultations in urban general practice in Mid-Norway anemia was found in 106 patients. Eighty-nine patients had their anemia worked out and treated by their general practitioner, 11 patients were referred to hospital or specialist, and in 6 patients no clear-cut reason for the anemia could be found. The patients could be broadly divided into four groups: iron deficiency in pregnancy (48%), iron deficiency secondary to bleeding (21%) anemia of chronic diseases (17%) and miscellaneous (7%).

Adolescent↗
PubMed1990

Anemia in general practice. Which laboratory tests are requested--how are the results interpreted and what are the consequences to patient care.

Laboratory tests requested in patients with anemia by general practitioners were recorded together with the diagnostic problem, the practitioners' interpretation of the test results and the consequences to the further work-up and treatment of the patients. There is broad agreement as to selection of tests to diagnose fairly well-established clinical entities. With more composite or complex disease patterns, the request patterns differ, not only with the diagnostic problem, but more so with the physicians. Some tests are requested with results very seldom outside the reference range (e.g. cobalamins and folate) and some on indications notoriously prone to give false positive results (e.g. serum iron in patients with anemia of chronic diseases). As part of future quality control programs proper use of laboratory tests should be important topics as joint projects between clinical chemists, general practitioners and clinicians.

Adolescent↗
PubMed1989

Localization of DNA repair synthesis by human cell extracts to a short region at the site of a lesion.

Double-stranded bacteriophage M13 DNA molecules were constructed containing a single specifically placed 2-(acetylamino)fluorene adduct or a single 4'-hydroxymethyl-4,5',8-trimethylpsoralen monoadduct. These circular DNA molecules were used to analyze in vitro DNA repair synthesis by cell extracts from normal human lymphoid cell lines. Both types of lesions stimulate DNA repair synthesis at the site of the adduct. DNA repair synthesis induced by the 2-(acetyl-amino)fluorene adduct took place in the damaged strand and was confined to a region within a 31-base pair restriction fragment around the adduct.

2-Acetylaminofluorene↗
PubMed1989

UvrABC incision of N-methylmitomycin A-DNA monoadducts and cross-links.

The Escherichia coli UvrABC endonuclease is a multisubunit enzyme that initiates the repair of a wide variety of DNA lesions in vivo by making dual incisions on a damaged strand at the eighth or ninth phosphodiester bond 5' and the fourth or fifth phosphodiester bond 3' to the modified base. It has been hypothesized that UvrABC is able to recognize a broad spectrum of lesions because it does not recognize the lesion per se but rather gross helical distortions that the lesion induces in the DNA. Several lesions have recently been studied which are thermal stabilizing and are not believed to distort the DNA grossly, including the CC-1065-N-3-adenine and anthramycin-N-2-guanine adducts. We have studied the activity of UvrABC in vitro on another thermal stabilizing and nondistortive adduct, N-methylmitomycin A (NMA), a bifunctional DNA-alkylating agent that reacts with guanine on the side facing the minor groove, yielding either monoadducts or interstrand cross-links. NMA adducts increase the thermal stability of DNA, and theoretical calculations indicate that NMA adducts do not grossly distort the DNA helix. Our results show that UvrABC makes incisions at the eighth phosphodiester bond 5' and the fifth phosphodiester bond 3' to an NMA monoadduct, consistent with the incision pattern observed for the majority of other lesions that are also recognized by UvrABC. DNA containing a site-specific NMA cross-link was also recognized and incised by UvrABC. The rate of incision of NMA cross-linked DNA was about 200-fold higher in supercoiled molecules than in relaxed molecules, whereas the rate of incision of DNA containing NMA monoadducts was stimulated approximately 2-fold by supercoiling. The signal for UvrABC recognition and incision of damaged DNA is discussed in relation to the ability of UvrABC to incise NMA adducts as well as other nondistortive lesions.

Base Sequence↗
PubMed1989

Diagnosis of major depression by self-report.

The Symptom Checklist-90 (SCL-90), Millon Clinical Multiaxial Inventory (MCMI), and Minnesota Multiphasic Personality Inventory (MMPI) test profiles of inpatients and outpatients with DSM-III major depression (n = 48) were contrasted with the test profiles of a control group of patients with diverse psychiatric disorders (n = 68). In addition, the diagnostic efficiency of the relevant depression subscales for the diagnosis of major depression were examined. The results indicated that the three self-report tests may be used to diagnose DSM-III major depression, and that the depressed patients had characteristic test profiles.

Adult↗
PubMed1989

Molecular cloning, sequence analysis and mRNA expression of human ADP-ribosylation factor.

The ADP-ribosylation factor (ARF) is the small (21 kb) GTP-binding protein required for the efficient cholera toxin-catalyzed ADP-ribosylation of purified Gs, the stimulating regulatory component of adenylate cyclase. Human ARF cDNA clones were obtained from a human cDNA library by cross-species hybridization with bovine ARF1, and the nucleotide and deduced amino acid sequences were determined. Comparison of the sequences of human and bovine ARF1 showed 90% identity at the nucleotide level and 100% identity at the amino acid level, demonstrating the highly conserved nature of the ARF protein. Using human ARF cDNA as the probe, we have detected ARF messenger RNA (approximately 2.2-2.3 kb) in a wide variety of human tissues and tumor cell lines.

ADP-Ribosylation Factor 1↗
PubMed1989

Supravital dithizone staining in the isolation of human and rat pancreatic islets.

Dithizone, a zinc chelating agent, is known to selectively stain the islets of Langerhans in the pancreas. In the present study, we have used this stain to aid the identification of islets in material obtained by collagenase digestion of human pancreas. Islets were shown to rapidly and reversibly stain red on incubation with dithizone solution. Tissue selected on the basis of dithizone staining was shown to contain insulin-positive cells and to accumulate insulin in the medium during a subsequent period in tissue culture. Experiments with rat islets indicated that the dithizone treatment had no effect on insulin release in tissue culture, on acute responses to stimulatory glucose concentrations or on the insulin content of cells. These results suggest that dithizone staining can assist in the identification of islets from the human pancreas and may prove to be a useful tool in developing techniques for the large scale isolation of functionally intact human islets.

Animals↗
PubMed1988

Structure of tumour necrosis factor by X-ray solution scattering and preliminary studies by single crystal X-ray diffraction.

The structure of tumour necrosis factor has been investigated by X-ray small-angle scattering and X-ray diffraction using synchrotron radiation. The overall radius of gyration is 25.5 A. A plausible model accounting for the scattering curves consists of an elongated trimer with an axial ratio of 3 to 4 and a maximal chord with a lower limit of 80 A. Tumour necrosis factor has been crystallized in a trigonal space group. Our results are in favour of a single trimer in the asymmetric unit. The diffraction extends to 3.5 A.

Humans↗