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J Reuben

Publications and source records attributed to J Reuben.

49 records · Page 3Linked to original sources
PubMed1975

Binding of manganese(II) to DNA and the competitive effects of metal ions and organic cations. An electron paramagnetic resonance study.

The binding of manganese(II) to DNA was studied by monitoring the concentration of free Mn2+ by electron paramagnetic resonance (EPR). It was found that the association constnat of the Mn-DNA complex depends upon the degree of saturation. The competitive effects of magnesium, calcium, sodium, and a number of organic cations including the antibiotic drug daunomycin were analyzed and the parameters describing the cation-DNA interaction were evaluated. It was found that the association constant as well as the parameter describing its dependence upon the degree of saturation decrease along the series Mn, Mg, Ca, Na. Differences in the extent of interaction with the base nitrogens (N-7) are suggested as the possible mechanisms leading to these observations. The EPR spectrum of the manganese-DNA complex was found to be similar to that of manganese-nucleotide complexes suggesting a similar mode of coordination. A comparison of the results of competitive and direct binding studies reveals some salient features of the small molecule-DNA interaction and leads to the conclusion that manganese binds at the major groove of the DNA helix.

Binding, Competitive↗
PubMed1975

The Alkali Ion-DNA Interaction as Reflected in the Nuclear Relaxation Rates of Na and Rb.

Longitudinal relaxation rates of (23)Na and (87)Rb in aqueous solutions of DNA were measured and interpreted in terms of contributions of "bound" and free species. The frequency dependence of the (23)Na relaxation rate sets an upper limit of 5.5 nsec for the correlation time characteristic of the alkali ion-DNA interaction. The plausible description of the alkali ion-DNA interaction emerging from the results is one in which the "bound" ions comprise a highly mobile ionic cloud around the lattice of phosphate groups with a population characterized by an apparent dissociation constant of 10.9 mM. Any specific binding to phosphate groups involving severe restrictions of motional freedom must be much (at least two orders of magnitude) weaker and of a very short duration (<5.5 nsec).

Journal Article↗
PubMed1971

Substrate anchoring and the catalytic power of enzymes.

Evidence from published nuclear magnetic resonance studies of enzyme-substrate and enzyme-inhibitor systems systems shows that substrates are confined at the active site of the enzyme, have a relatively long residence time, and tumble in solution as an enzyme-substrate complex. The consequences of this "substrate anchoring" with regard to the catalytic power of enzymes are considered. It appears that as a result of the relatively slow motions, the probability of existence of the "activated complex" in the enzymatic reaction may be increased and thus the reaction rate may be accelerated by factors of between 10(6) and 10(9). It is estimated that the combined effect of substrate anchoring, desolvation, and charge compensation may lead to reaction-rate accelerations by factors of between 10(9) and 10(8).

Alcohol Oxidoreductases↗
PubMedDate not supplied

Comparative functional analysis of lymphocytes and monocytes from plateletapheresis.

Large numbers (2.9 +/- 1.2 X 10(9)) of mononuclear cells can be obtained from incidental samples collected during routine plateletapheresis. We conducted studies comparing characteristics and functions of mononuclear cells derived from venous blood samples and from routine plateletapheresis in the same normal donors. Cell viability was similar in both samples (96 +/- 1% plateletapheresis vs 97 +/- 2% venous blood). Higher concentration of monocytes were observed in the plateletapheresis samples (32.3 +/- 6%) than in the venous blood (14.3 +/- 4%). The procedure of plateletapheresis does not seem to alter lymphocyte or monocyte function. Thus, the functional integrity of these cell populations was demonstrated in terms of natural killer cell activity, blastogenic response to mitogens, local graft-versus-host reactions, monocyte-mediated antibody-dependent cellular cytotoxicity against human red cells, monocyte-mediated tumor cell cytotoxicity, latex phagocytosis, and monocyte-dependent lymphocyte blastogenesis. We conclude that monocytes and lymphocytes obtained during routine plateletapheresis are functionally intact.

Antibody-Dependent Cell Cytotoxicity↗
PubMedDate not supplied

The attenuation of hemorrhage-induced liver injury by exogenous nitric oxide, L-arginine, and inhibition of inducible nitric oxide synthase.

We investigated the role of nitric oxide (NO) in its ability to reduce liver injury in an animal model of hemorrhagic shock (HS). Ninety-six Sprague-Dawley rats weighing 250 to 300 g were divided in 6 groups (n = 16 per group) that included treatment at the beginning of resuscitation with normal saline (groups 1, 3) sodium nitroprusside (NP) (0.5 mg/kg) (groups 2, 4) L-arginine (300 mg/kg) (group 5), and L-N6-(1-iminoethyl) lysine (L-NIL, 40 mg/kg) (group 6). The experimental model of HS consisted of the withdrawal of 3 mL blood per 100 g in a 15-min period, tail amputation (75%), and drug administration at 30 min. This was followed by fluid resuscitation (FR) with lactated Ringer's (LR) solution to reach a mean arterial pressure (MAP) of 40 mm Hg, then a hospital phase of 60 min with hemostasis and FR with LR solution to reach a MAP of 70 mm Hg with a 3-day observation phase. NP, L-Arginine, and L-NIL significantly reduced fluid requirements for resuscitation (p =.0001) as well as significantly increased MAP after resuscitation from hemorrhage. We also observed an improved statistically significant difference (p =.001) in tests demonstrating less hepatic injury and histology damage. The mRNA expression of cytokines in the liver (interleukin [IL]-1alpha, IL-beta1, tumor necrosis factor [TNF]beta, IL-3, IL-4, IL-5, IL-6, IL-10, TNFalpha, IL-2, interferon [IFN]gamma) was reduced by NP treatment, L-arginine, and L-NIL. These data suggest that excess NO mediates hemorrhage-induced liver injury and that the suppression of inducible nitric oxide synthase (iNOS)-generated NO bioavailability with the NO donor sodium nitroprusside may reduce the pathophysiologic consequences of severe hemorrhage. This effect could be possibly related to the scavenging of to superoxide radicals (O2-) or the blockade of the deleterious effects of TNF and other inflammatory cytokines. The protective action noted with L-arginine cannot be fully explained within the context of this article, although it could be most likely associated with the supplementation of eNOS-generated NO.

Animals↗
PubMedDate not supplied

Expression of transferrin receptors is unrelated to proliferative status in cultured human colon cancer cells.

Transferrin is an iron-carrying compound that stimulates cell growth and division by binding to specific receptors (TR) which are preferentially expressed by actively growing cells or by the malignant counterpart of normal cells. However, quiescent cells may not necessarily cease expressing TR. We evaluated TR expression by flow cytometric analysis utilizing a monoclonal antibody (OKT-9) specific for TR on six established human colon cancer cell lines with distinct degrees of phenotypic differentiation and growth rates at sequential stages of in vitro growth (exponential and stationary phase). There were no significant differences in the proportion of cells expressing TR among the fast and slow growing cell lines at any time point of the study, nor did the cultures change the proportion of TR positive cells in their transit from exponential into stationary phase of growth. Hence, direct measurements of TR expression in malignant cell populations may not provide a useful clinical marker to distinguish highly proliferative tumors from those with a slower growth resulting from a larger proportion of quiescent cells.

Antibodies, Monoclonal↗