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Biomedical subjects

B Kaplan

Publications and source records attributed to B Kaplan.

At least 379 records · Page 21Linked to original sources
PubMed1989

Abasic frameshift in DNA. Solution conformation determined by proton NMR and molecular mechanics calculations.

We have determined the three-dimensional structure of a non-self-complementary oligodeoxynucleotide duplex that contains a model abasic site. The duplex contains six GC base pairs plus the abasic site at the center of one strand and corresponds to an abasic frameshift. Two-dimensional NMR studies on the nonexchangeable protons show that the guanine bases on either side of the abasic site are stacked over each other and that the abasic site is rotated out of the helix. Close proton-proton interactions are observed between the H4' proton of the abasic site and sugar protons of the guanosine in the 5' direction, which allows the position of the free sugar to be well-defined. NOE buildup curves from NOESY spectra recorded at very short mixing times were used to calculate a set of interproton distances. This data set was incorporated into the refinement of the oligonucleotide structure by molecular mechanics calculations. Two conformations that differ in the sugar conformation of the guanosine next to the abasic site in the 3' direction were necessary to fit all the NMR data. One of these two conformations could only be stabilized by addition of counterions at specific sites.

Chemical Phenomena↗
PubMed1989

Ionized and wobble base-pairing for bromouracil-guanine in equilibrium under physiological conditions. A nuclear magnetic resonance study on an oligonucleotide containing a bromouracil-guanine base-pair as a function of pH.

A one and two-dimensional nuclear magnetic resonance study of a non-selfcomplementary oligonucleotide containing a central 5-bromouracil-guanine pair is reported. For these two bases three types of hydrogen bonding schemes could exist; wobble, rare tautomer and ionized. The two-dimensional spectra of non-exchangeable protons together with one-dimensional spectra recorded in water show that at pH 7.0 the predominant species is a right-handed B-form DNA in which the brU.G pair has wobble geometry. On raising the pH we observe a transition monitored by proton chemical shift changes for the brU.G and adjacent base-pairs. The mid-point of the transition was observed at pH 8.6. Spectra recorded at pH 9.8 show that the helix remains intact with B form conformation. It is shown that this high pH form has an ionized brU.G base-pair now in Watson-Crick geometry. Thus under physiological conditions an equilibrium exists between wobble and ionized structures.

Base Composition↗
PubMed1989

Bound amino acids in uremic sera: search for peptidic middle molecules by preparative polyacrylamide gel electrophoresis and high performance liquid chromatography.

The samples of normal and uremic sera were ultrafiltered, separated on SEP-PAK C18 cartridges and subjected to sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The serum material extracted from the slab gel was purified from SDS and further fractionated by reverse-phase high performance liquid chromatography (HPLC). The obtained fractions were examined by amino acid analysis and mass spectrometry. An increased number of moderately polar fractions containing bound amino acids was found in sera of uremic patients on hemodialysis. Two most prominent uremic fractions corresponded to N-benzoylglycine (hippuric acid) (fraction I, k' = 9,4) and phenylacetylglutamine (fraction II, k' = 9,7). Increased amounts of bound glutamine, glycine, serine, leucine, asparagine, alanine, valine, phenylalanine were found in other moderately polar uremic fractions. These fractions (k' range from 12.1 to 13.2) contained no free amino acids, nor any other known small uremic serum compounds; they were considered as peptide 'middle molecules' (MM) of a molecular mass smaller than 1700.

Amino Acids↗
PubMed1989

Continuous measurement of cerebral cortical blood flow by laser-Doppler flowmetry in a rat stroke model.

Laser-Doppler flowmetry (LDF), a new method allowing instantaneous, continuous, and noninvasive measurements of microcirculatory blood flow in a small tissue sample, was evaluated for its accuracy in monitoring regional cerebral blood flow (rCBF) in the cortical microcirculation after focal cerebral ischemia. Wistar and spontaneously hypertensive rats (SHR, n = 19) were subjected to permanent occlusion of the middle cerebral and common carotid arteries. Absolute rCBF in a tissue sample of the ischemic hemisphere was measured autoradiographically with [14C]iodoantipyrine as a tracer and compared to rCBF measured by LDF. Additionally, the percent change in rCBF between baseline and ischemic values was compared for both methods. Absolute rCBF values recorded with LDF correlated poorly (r = 0.54) with [14C]iodoantipyrine measurements. In contrast LDF readings expressed as a percentage of ischemic vs. preocclusion readings (relative LDF readings) correlated very well (r = 0.91) with the percent change in [14C]iodoantipyrine measurements. We conclude that LDF does not provide accurate measurements of absolute rCBF values but this method allows accurate measurements of changes in rCBF due to induction of focal cerebral ischemia.

Animals↗
PubMed1989

Acute myeloid leukemia, FAB M-1 microgranular variant: a multiparameter study.

Acute leukemia was diagnosed in 62 adults and children over a recent 13-month period. Using light microscopy, cytochemical profiles, surface markers, and cytogenetics, 25 cases were classified as acute myeloid leukemia (AML) and 32 as acute lymphoblastic leukemia (ALL). The remaining 5 cases of de novo acute leukemia were unclassifiable. The routine cytochemical battery used on these 62 cases included: myeloperoxidase, sudan black B, nonspecific esterase, and periodic acid-Schiff (PAS). Flow markers utilized were: T3, T4, T5, T8, T10, T11, B1, B4, kappa, lambda, Ia, CALLA, Mo1, Mo2, My4, My7, My8, and My9. TdT was performed by immunoperoxidase and ELISA methods. The five unclassified cases were cytochemically negative and expressed no B- or T-cell-specific antigens, or TdT positivity. The morphologic differential diagnosis was between FAB L-2 and M-1. Karyotypic abnormalities involving chromosomes 3 and 7 were suggestive of myeloid origin in 2 of 4 patients studied. Flow cytometry demonstrated My7 on greater than 50% of blasts from two cases. Myeloperoxidase ultracytochemistry showed reaction product in small primary granules of blasts from all 5 cases. Positive cells contained only 1-2 granules/cell profile. The number of positive cells per case was in the range 10-20%. We conclude from this study that ultracytochemistry is very useful in providing definitive diagnosis and accurate subclassification of some AML FAB M-1 cases, particularly when light microscopic cytochemistry, cytogenetics, and flow cytometric markers are noncontributory. We propose to designate these acute "unclassified" leukemias as AML FAB M-1 "microgranular" type.

Acute Disease↗
PubMed1988

Equilibrium between a wobble and ionized base pair formed between fluorouracil and guanine in DNA as studied by proton and fluorine NMR.

A synthetic oligonucleotide duplex containing the chemotherapeutic and mutagenic agent 5-fluorouracil paired with guanine has been studied in solution by proton and fluorine NMR. The 7-mer duplex containing a central FU.G base pair adopts a normal right-handed configuration. At low pH, the predominant base-paired structure is wobble, whereas at higher pH an ionized structure in Watson-Crick geometry is observed. The two structures are in a pH-dependent equilibrium with one another with an apparent pK of 8.3 at 23 degrees C. This is the first demonstration of an equilibrium between two distinct base pairing schemes and the first demonstration of a negatively charged base pair in DNA.

Base Composition↗
PubMed1988

Glioblastoma in the older patient: how long a course of radiotherapy is necessary?

Eighteen patients over 60 years old with a histologically proven diagnosis of glioblastoma multiforme were treated by a short radiotherapy course (3000 cGy midline dose by two opposed portals to the whole brain). Results in terms of survival and function appeared to be as good as with the standard course of six to seven weeks as reported in the literature.

Age Factors↗
PubMed1988

Up-regulatory effect of triphasic oral contraceptive on platelet 3H-imipramine binding sites.

Triphasic oral contraceptive (Logynon) induced a significant increase (36%) in the maximal binding capacity of platelet membranes for [3H]imipramine. The increase was achieved in the second Logynon cycle as compared to pretreatment and first Logynon cycle binding values. The pill contains a combination of ethinyl estradiol and levonorgestrel, and it is as yet unclear which of the two hormones is responsible for the up-regulatory effect. The increase in the density of platelet imipramine binding sites may reflect a similar alteration in brain. The increase in imipramine binding did not correlate with alteration in mood as assessed by Beck Depression Inventory scores.

Adult↗
PubMed1988

Poststeroid panniculitis: a case report.

Firm, red, subcutaneous plaques developed on the cheeks of a 19-month-old girl during a one-month period of rapid steroid withdrawal. The clinical features were most consistent with poststeroid panniculitis. This rare complication of steroid therapy should be differentiated from other causes of red cheeks in children.

Diagnosis, Differential↗
PubMed1988

Menstrual function and hirsutism in patients with gonadal dysgenesis.

Thirty adult patients with gonadal dysgenesis were identified over the five-year period between January 1981 and December 1985 in the Reproductive Endocrinology and Infertility Clinic at the University of Southern California/Los Angeles County Medical Center. Six patients had previous menstrual function and presented with secondary amenorrhea. Chromosome analysis revealed three patients with 45,X karyotypes and three patients with 45,X mosaics. One of these patients (45,X/47,XXX) presented with secondary amenorrhea and elevated follicle-stimulating hormone, and conceived twice after being placed on estrogen replacement therapy. Three additional patients presented with hirsutism as their primary complaint, and had karyotypes of 45,X/46,XY, 45X/46X,i(Yq), and 45,X. The latter patient, who had her karyotype confirmed by analysis of four tissue sources, had a streak gonad and a dysgenetic gonad, with both follicles and seminiferous tubules.

Adolescent↗