Felice Aull

Interactions of lectins with plasma membrane glycoproteins of the Ehrlich ascites carcinoma cell.

Several aspects of the interaction of various lectins with the surface of Ehrlich ascites carcinoma cells are described. The order of agglutinating activity for various lectins is Ricinus communis greater than wheat germ greater than or equal to concanavalin A greater than or equal to soybean greater than Limulus polyphemus. No agglutination was noted for Ulex europaeus. Using 125I-labeled lectins it was determined that there are 1.6 and 7 times as many Ricinus communis lectin binding sites for concanavalin A and soybean lectins. Sodium deoxycholate-solubilized plasma membrane material was subjected to lectin affinity chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The lectin receptors of the plasma membrane appeared to be heterogeneous and some qualitative differences could be discerned among the electrophoretically analyzed material, which bound to and was specifically eluted from the various lectin affinity columns. The characteristics of elution of bound material from individual lectin columns indicated secondary hydrophobic interactions between concanavalin A or wheat germ agglutinin and their respective lectin receptor molecules.

Potassium chloride cotransport in steady-state ascites tumor cells Does Bumetanide inhibit?

Bumetanide is a potent diuretic drug which has some structural features in common with furosemide. The steady-state exchange of K+ and Cl- was investigated in Ehrlich ascites tumor cells treated with bumetanide. This agent did not alter the cellular content of K+ or Cl- but the self-exchange of both ions was depressed. K+ self-exchange was inhibited by 55% at bumetanide concentrations as low as 10(-6) M. Cl- self-exchange was less sensitive to this drug but at low concentrations (between 10(-6) and 10(-3) M) bumetanide was a more effective inhibitor of Cl- transfer than furosemide. The steady-state K+ flux of cells equilibrated in NO3- media was compared with the K+ flux in cells treated with 10(-4) or 10(-3) M bumetanide; the Cl(-)-sensitive K+ exchange was equivalent to the bumetanide-sensitive K+ exchange. Since the results suggested that a bumetanide-sensitive (Cl-, K+) cotransport could be operative in steady-state cells, the stoichiometry of the bumetanide-sensitive fluxes was determined by measuring Cl- and K+ fluxes simultaneously in the same cell suspension. At 5 . 10(-4) and 10(-3) M bumetanide concentrations, the ratio of these fluxes was 0.98 +/- 0.07 (S.E.) and 1.04 +/- 0.06, respectively, consistent with the postulated cotransport mechanism. At 10(-4) and 10(-5) M, however, the ratio of the bumetanide-sensitive Cl-/K+ flux was significantly less than 1.0. Since the magnitude of the bumetanide-sensitive K+ flux at 10(-4) M was close to that of the Cl(-)-sensitive flux, a ratio of less than 1.0 at this drug level indicates that Cl-sensitivity and drug sensitivity may not reflect inhibition of the same process under all circumstances.

Purification of a hemagglutinin from Limulus polyphemus by affinity chromatography.

Summary A. hemagglutinin has been isolated from the hemolymph of the common horseshoe crab ( Limulus polyphemus ) using affinity chromatography as the primary purification procedure. The hemagglutinin specifically binds to a bovine submaxillary mucin (BSM) affinity gel and is subsequently released upon the addition of Na citrate to the elution buffer. The purity of the final product was attested to by polyacrylamide gel electrophoresis, electron microscopic observation and by a greater than 1500-fold increase in specific activity as compared to the starting material. The purified hemagglutinin was able to give a precipitin reaction in immunodiffusion gels against purified BSM but not against desialated BSM.

Medical humanities at New York University School of Medicine: an array of rich programs in diverse settings.

The New York University School of Medicine has a rich tradition of cultivating programs in medical humanities and professionalism. They are drawn from the departments, centers, students, and faculty in the School of Medicine, have linkages throughout the university, and are interwoven into the fabric and culture of the institution. Some are centrally based in the School of Medicine’s deans’ office, and others are located in individual departments and receive support from the dean’s office. This article describes representative programs for medical students and faculty. Curricular initiatives, the fundamental components of medical students’ learning, include a course entitled “The Physician, Patient, and Society,” a clerkship essay in the Medicine Clerkship, an opportunity for reflection during the medicine clerkship, and a medical humanities elective. In 2002, the Professionalism Initiative was launched to enhance and reflect the values of the medical profession. Its curriculum consists of a series of events that coordinate, particularly, with existing elements of the first-year curriculum (e.g., orientation week, a session during anatomy, a self-assessment workshop, and a peer-assessment workshop). The Master Scholars Program is a group of five, theme-based master societies consisting of faculty and students who share common interests around the society’s themes. Programs developed for the societies include colloquia, faculty-led seminars, a mandatory student-mentoring program, and visiting scholars. Finally, the authors describe three high-quality literary publications created at New York University School of Medicine. Each of the initiatives undergoes regular critical examination and reflection that drive future planning.

Saturation behavior of ascites tumor cell chloride exchange in the presence of gluconate

Steady state Cl- flux across the Ehrlich mouse ascites cell membrane was studied when gluconate replaced Cl- in the external medium. Saturation behavior was observed; K 1/2 was 23.9 mM Cl- and V was 758 micromol.g-1 dry weight.h-1. The cells lost K+, Cl- and H2O, consistent with relative impermeability to gluconate, and the Cl- efflux rate coefficient was elevated. The results indicate that a major portion of Cl- exchange occurs as a membrane transport process and suggest that the process is sensitive to intracellular Cl- levels.

Evidence for Conformational Changes in Concanavalin A Upon Binding of Saccharides as Determined from Solvent Water Proton Magnetic Relaxation Rate Dispersion Measurements

In previous studies of the interaction of solvent water molecules with the Mn++ ion in Mn-Con A by observation of the dispersion of the spin-lattice relaxation rate (T) of the solvent water protons over a wide range of magnetic fields (Koenig et al., 1973), we have shown that this rate is dominated by the residence time of a single exchanging water ligand on the Mn++ ion. In limited measurements at low fields, we also observed that the binding of α- or β- methyl-D-glucopyranoside to Mn-Con A decreased the relaxation rate by approximately 15 percent. In the present study, we have measured the effects of binding of a series of mono- and oligosaccharides on the solvent water proton relaxation rate over a range of magnetic fields from 5 Oe to 12 KOe and show that the observed decrease in the relaxation rate is due to an increase in the residence time of the single exchanging water ligand. This effect is consistent with a conformational change in the protein upon binding of saccharides. We find that the binding of α- and β- methyl-D-glucopyranoside, α- methyl-D-mannopyranoside and β-(o-iodophenyl)-D-glucopyranoside produce the same increase in residence time and therefore the same conformational change in the protein, whereas galactose and β- (o-iodophenyl)-D-galactopyranoside show no effects. The same reduction in relaxation rate as that caused by the above monosaccharides was observed with the following oligosaccharides: D-maltose, D-maltotriose, D-maltotetraose, o-α-D-mannopyranosyl-(1→2)-D-mannose, o-α-D-mannopyranosyl-(1→2)-o-α-D-mannopyranosyl-(1→2)-D-mannose, o-α-D-mannopyran-osyl-(1→2)-o-α-D-mannopyranosyl-(1→2)-0-α-D-mannopyranosyl-(1→2)-D-mannose and melezitose. As observed by Goldstein and co-workers, the first three oligosaccharides have nearly the same affinity constant, whereas the α-(1,2) linked mannans show increasing affinity constants with increasing chain length. Melezitose also shows enhanced binding by a factor of four relative to α-methyl-D-glucopyranoside. The water relaxation data suggest that the above mono- and oligosaccharides bind to Con A by a similar mechanism involving only a single saccharide residue combined with the protein at one time. Determination of the enthalpy (∆H) and entropy (∆S) of binding of maltotriose and melezitose indicates that the factor of 8 difference in their affinity constants is due to different ∆S values. This suggests that the greater affinity of melezitose is due to the presence of two glucose residues in the molecule, either of which is capable of binding to the same site on the protein. The increased probability of binding for melezitose results in a larger forward rate constant relative to maltotriose which has only one glucose residue which can bind to the protein. Thus, the greater affinity of the α-(1→2)-mannose oligosaccharides appears to be due to a statistical increase in probability of binding because of the presence of more than one binding residue in the chain and not to an extended binding site on the protein.

Observing boundaries in conversations with patients.

Suggests to medical students what forms of self-disclosure are acceptable during clinical encounters and when self-disclosure might be interpreted by patients as taking attention away from them. Virtual Mentor is a monthly bioethics journal published by the American Medical Association.