Strain differences of interferon-generating capacity and resistance in toxoplasma-infected mice

To explore a possible correlation between susceptibility to Toxoplasma and interferon (IFN)-generating capacity in mice, we compared the levels of serum IFN induced by stimulation with Toxoplasma lysate antigen (TLA) in different strains of Toxoplasma-infected and uninfected mice. Injection of TLA into five strains of mice with chronic Toxoplasma infection resulted in the release of considerable amounts of IFN into the circulation. Most of these IFN activities were acid labile and not neutralized by sheep antiserum against mouse IFN-alpha/beta, indicating that IFN-gamma was the dominant form produced in this system. In contrast, the majority of IFN induced in uninfected mice was characterized as IFN-alpha/beta by their acid stability and antigenicity. The response of IFN production in Toxoplasma-infected and uninfected mice varied quantitatively depending on the mouse strains examined. C57BL/6 mice were found to be the best producers of both IFN-alpha/beta and IFN-gamma, while BALB/c mice were consistently poor producers of both IFN populations. A/J, DBA/2, and C3H/He mice could be roughly classified as intermediate producers of both IFN populations. C57BL/6 and C3H/He mice showed a significant prolongation of mean survival time following primary or secondary infection with Toxoplasma compared to that of BALB/c mice. However, there was no direct correlation between the susceptibility to Toxoplasma and the levels of serum IFN.     

Accessibility of phosphatidylethanolamine in bacteriophage PM2 and in its gram-negative host.

The reaction of trinitrobenzenesulfonic acid with phosphatidylethanolamine in the cytoplasmic membrane of Alteromonas espejiana suggests that 50% of this lipid occupies the outer lamella. In PM2, similar analysis suggests that 56% of this lipid populates the outer lamella of the membrane, the surface of which accounts for 60% of the membrane area.     

Regulation by divalent cations of 3H-baclofen binding to GABAB sites in rat cerebellar membranes

When investigating the effects of divalent cations (Mg2+, Ca2+, Sr2+, Ba2+, Mn2+ and Ni2+) on 3H-baclofen binding to rat cerebellar synaptic membranes, we found that the specific binding of 3H-baclofen was not only dependent on divalent cations, but was increased dose-dependently in the presence of these cations. The effects were in the following order of potency: Mn2+ congruent to Ni2+ greater than Mg2+ greater than Ca2+ greater than Sr2+ greater than Ba2+. Scatchard analysis of the binding data revealed a single component of the binding sites in the presence of 2.5 mM MgCl2, 2.5 mM CaCl2 or 0.3 mM MnCl2 whereas two components appeared in the presence of 2.5 mM MnCl2 or 1 mM NiCl2. In the former, divalent cations altered the apparent affinity (Kd) without affecting density of the binding sites (Bmax). In the latter, the high-affinity sites showed a higher affinity and lower density of the binding sites than did the single component of the former. As the maximal effects of four cations (Mg2+, Ca2+, Mn2+ and Ni2+) were not additive, there are probably common sites of action of these divalent cations. Among the ligands for GABAB sites, the affinity for (-), (+) and (+/-) baclofen, GABA and beta-phenyl GABA increased 2-6 fold in the presence of 2.5 mM MnCl2, in comparison with that in HEPES-buffered Krebs solution (containing 2.5 mM CaCl2 and 1.2 mM MgSO4), whereas that for muscimol was decreased to one-fifth. Thus, the affinity of GABAB sites for its ligands is probably regulated by divalent cations, through common sites of action.     

Continuous production of L-aspartic acid by immobilized aspartase

Various methods were tried for the immobilization of aspartase, and the preparation having the highest activity was obtained when partially purified aspartase from Escherichia coli was entrapped into polyacrylamide gel Iattice. Enzymatic properties of the immobilized aspartase were investigated and compared with those of the native aspartase. With regard to optimum pH, temperature, concentration of Mn⁺⁺, kinetic constants and heat stability, no marked difference was observed between the native and immobilized aspartases. By employing an enzyme column packed with the immobilized aspartase, conditions for continuous production of L -aspartic acid from ammonium fumarate were investigated. When a solution of 1M ammonium fumarate (pH 8.5, containing 1mM MnCl₂) was passed through the aspartase column at the flow rate of SV = 0.08 at 37°C, the highest rate of reaction was attained. From the column effluents, L-aspartic acid was obtained in a good yield.