Identification of a GM1-Binding Protein on the Surface of Murine Neuroblastoma Cells

S20Y murine neuroblastoma cells appear to express a protein component(s) able to adhere specifically to the oligosaccharide portion of GM1 (oligo-GM1). To identify proteins with which the oligo-GM1 becomes closely associated, a radiolabeled (125I), photoactivatable derivative of oligo-GM1 was prepared. This was accomplished by reductive amination of the glucosyl moiety of oligo-GM1 to 1-deoxy-1-aminoglucitol, followed by reaction of the amine with sulfosuccinimidyl 2-(p-azidosalicylamido)ethyl-1,3'-dithiopropionate (SASD). Crosslinking studies using the photoactivatable probe indicated that it came in close proximity to a protein with an apparent molecular mass of approximately 71 kDa. In competition experiments, as little as a 10-fold molar excess of oligo-GM1 resulted in a selective reduction in labeling of this protein; preincubation with a 200-fold molar excess of siayllactose was necessary to observe the same change in the labeling pattern, lending additional support to the hypothesis that the approximately 71-kDa protein specifically associates with oligo-GM1. Cell surface location of the oligo-GM1 binding protein was confirmed using subcellular fractionation and morphological analyses.     

Hemoglobin Dallas (alpha 97(G4)Asn-->Lys): functional characterization of a high oxygen affinity natural mutant.

Hemoglobin Dallas, an alpha-chain variant with a substitution of lysine for asparagine at position 97(G4), was found to have increased oxygen affinity (p1/2 = 1 mmHg at pH 7.3 and 20 degrees C), diminished cooperativity (n, the Hill coefficient = 1.7) and reduced Bohr effect (about 50%). Addition of allosteric effectors (such as 2,3-diphosphoglycerate, inositol hexakisphosphate and bezafibrate) led to a decrease in oxygen affinity and increase in cooperative energy. Kinetic studies at pH 7.0 and 20 degrees C revealed that (i), the overall rate of oxygen dissociation is 1.4-fold slower than that for HbA and (ii), the carbon monoxide dissociation rate is unaffected. The abnormal properties of this hemoglobin variant can be attributed to a more 'relaxed' T-state.     

Circulating immune complexes in the pathogenesis of recurrent erysipelas

The dynamics of circulating immune complexes (CIC) in comparison with the level of SH-groups of serum deproteinate and other characteristics of cell-mediated and humoral immunity (the reaction of the inhibition of antibodies, the levels of T-cells and their main subpopulations) was studied in 103 erysipelas patients and in 46 persons having had the disease at the acute period of this infection and at the periods between relapses. The elevated levels of CIC and SH-groups of serum deproteinate were found to be directly correlated with the inhibition index. The study showed that, as a rule, in patients with the elevated level of CIC the frequently relapsing form of erysipelas, accompanied by the formation of relative hypersuppressor-type secondary immunodeficiency and by a decrease in the functional activity of dermal macrophages, was observed.     

Binding of lipoproteins to inert materials revisited with computer-assisted analysis

A number of studies conducted in the last decade showed that saturable ('specific') binding, by itself, does not necessarily imply biological significance. That is, biological ligands were shown to bind to inert materials as well as to biological receptors in a saturable manner. In these studies specific binding was operationally defined as binding that was displaceable by excess concentrations of unlabeled ligand. This method of measuring specific binding is now no longer considered optimal. To investigate whether optimal (computer-assisted) techniques of measuring specific binding--namely, nonlinear least-squares curve fitting of total binding data, with mathematical separation of the total binding into its various components--might ensure biological significance of measured specific binding, we studied the binding of high-density lipoproteins (HDL3) to tissue culture dishes as an example of binding without biological significance. This binding closely followed the paradigm of a ligand interacting with a class of homogeneous, saturable sites and with a class of relatively unsaturable sites, just as it would have if the HDL3 were interacting with an unpurified biological receptor. This finding indicates that computer-assisted analysis, while most accurately describing binding data, nevertheless does not ensure that measured specific binding has biological significance. Saturability is such a nonselective feature of equilibrium binding data that it should probably no longer be considered one of the criteria for deciding whether or not a defined binding site is a receptor.     

Round robin investigation of methods for recovering human enteric viruses from sludge

To select a tentative standard method for detection of viruses in sludge the American Society for Testing and Materials D19:24:04:04 Subcommittee Task Group initiated round robin comparative testing of two procedures that, after initial screening of several methodologies, were found to meet the basic criteria considered essential by the task group. Eight task group member laboratories agreed to perform round robin testing of the two candidate methods, namely, The Environmental Protection Agency or low pH-AlCl3 method and the Glass or sonication-extraction method. Five different types of sludge were tested. For each particular type of sludge, a single laboratory was designated to collect the sludge in a single sampling, make samples, and ship it to the participating laboratories. In most cases, participating laboratories completed all the tests within 48 h of sample arrival. To establish the reproducibility of the methods, each laboratory tested each sludge sample in triplicate for the two candidate virus methods. Each processed sludge sample was quantitatively assayed for viruses by the procedures of each individual round robin laboratory. To attain a more uniform standard of comparison, a sample of each processed sample from all laboratories was reassayed with one cell line and passage number by a single laboratory (Environmental Protection Agency Environmental Monitoring and Support Laboratory, Cincinnati, Ohio). When the data were statistically analyzed, the Environmental Protection Agency method was found to yield slightly higher virus recoveries for all sludge types, except the dewatered sludge. The precisions of both methods were not significantly different.(ABSTRACT TRUNCATED AT 250 WORDS)     

Use of low-dose insulin infusions in diabetics after myocardial infarction

Myocardial infarction in diabetics is often accompanied by poor diabetic control. An assessment of a low-dose insulin infusion regimen in 26 diabetic patients after myocardial infarction found this system to be simple, effective, and safe.     

Comparative analysis of respiratory activity in the wild type strain of <Emphasis Type="Italic">Neurospora crassa</Emphasis> and its photoreceptor complex mutants

Cell respiratory activity of protoplasts obtained from the wild type of Neurospora crassa and photoreceptor complex WCC—white collar 1 (wc-1) and white collar 2 (wc-2)—mutants of Neurospora crassa strains was investigated. Respiration inhibition by KCN in the presence of 25 mM succinate was similar in all strains and did not exceed 83–85% against control. The significant induction of KCN-resistant respiratory pathway occurred under 1% glucose oxidation in wc-1 and wc-2 mutants if compared with the wild type strains. The inhibitors of the main (cytochrome) pathway of electron transfer in mitochondria—1 mM KCN and antimycin A (4 μg/ml)—blocked the respiration rate of the protoplasts from N. crassa wild type by 75%, while the cell respiration of wc-1 and wc-2 strains was suppressed by approximately 50%. The specific inhibitor of alternative oxidase—10 mM salicylhydroxamic acid (SHAM)—in combination with the blockers of mitochondrial electron transfer chain caused the total suppression of respiratory activity of protoplasts in all studied strains. It is supposed that an increase of KCN-resistance in WCC mutants under glucose oxidation is connected with alternative oxidase activation as the result of failure in reception and signal transduction of active oxygen species.     

Hormonal regulation of anabolic processes and of protein utilization efficiency in the early postnatal period

The levels of thyroid, pituitary and steroid hormones-thyroxine, triiodothyronine and 11-hydroxycorticosteroids in the blood serum, somatotropin in the pituitary, and processes of protein assimilation were studied in rats in the early postnatal period. The highest endogenous production of thyroxine, triiodothyronine and somatotropin was detected in 15-day-old rats. The highest level of protein utilization was detected in 7 to 15-day-old rats, followed by the lowering of the utilization on changing over to definitive nutrition. Endogenous production of the anabolic hormones thyroxine, triiodothyronine and somatotropin was found to correlate with a high level of protein utilization in rats within the first days of life after birth.     

Regulation of adenylate cyclase in E. coli

The intracellular concentrations of cAMP in Escherichia coli are regulated mainly by control of the activity of adenylate cyclase. Withdrawal of the carbon source from the growth medium causes a gradual reduction of cellular energy and a dramatic stimulation of cyclase activity. Manipulations of the proton gradient at the cell membrane of ATP synthase-deficient E. coli (unc-) revealed that this part of the energy compartment is not responsible for the starvation-induced stimulation of cyclase. Neither is the ATP pool involved in regulation of the activity of the cyclase. The intracellular concentrations of ATP were experimentally lowered by purine starvation of auxotrophs, by inhibition of purine synthesis using amethopterin, or by affecting ATP synthesis using arsenate. None of these conditions led to stimulation of cyclase activity. The control of cyclase is exerted not via the energy pools but via uptake systems of energy substrates independent of whether the substrate can be metabolized or not, or how the transport is energized. The stringent coupling between these transport systems and cyclase activity enables the cell to react instantaneously to changes in its environment.