Neutralizing monoclonal antibodies against human immunodeficiency virus type 2 gp120.

Monoclonal antibodies (MAbs) were obtained by immunizing mice with synthetic peptides corresponding to the third variable (V3) or the third conserved (C3) domain of the external envelope protein (gp120) of human immunodeficiency virus type 2 (HIV-2ROD). One MAb, designated B2C, which was raised against V3 peptide NKI26, bound to the surface of HIV-2-infected cells but not to their uninfected counterparts. B2C was capable of neutralizing cell-free and cell-associated virus infection in an isolate-specific fashion. The antibody-binding epitope was mapped to a 6-amino-acid peptide in the V3 variable domain which had the core sequence His-Tyr-Gln. Two MAbs, 2H1B and 2F19C, which were raised against the C3 peptide TND27 reacted with gp120 of HIV-2ROD in a Western immunoblot assay. The C3 epitopes recognized by these two MAbs appeared inaccessible because of their poor reactivity in a surface immunofluorescence assay. Although partial inhibition of syncytium formation was observed in the presence of the anti-C3 MAbs, their neutralizing activity appeared weak. Finally, the effects of these MAbs against CD4-gp120 binding were assessed. Partial inhibition of CD4-gp120 binding was observed in the presence of high concentrations of B2C. On the other hand, no inhibition of CD4-gp120 binding was observed in the presence of anti-C3 MAbs. Since complete neutralization could be achieved at a concentration corresponding to that of partial binding inhibition by B2C, some different mechanisms may be involved in the B2C-mediated neutralization. These results, taken together, indicated that analogous to the function of the V3 region of HIV-1, the V3 region of HIV-2ROD contained at least a type-specific fusion-inhibiting neutralizing epitope. In this respect, the V3 sequence of HIV-2 may be a useful target in an animal model for HIV vaccine development.     

Switching dynamics and the transient memory storage in a model enzyme network involving Ca2+/calmodulin-dependent protein kinase II in synapses

 The signal processing through a chain of phosphorylation-dephosphorylations mediated by a pair of enzymes, Ca²⁺/calmodulin-dependent protein kinase II and the associated phosphatase, is formulated as a non-autonomous dynamical system in the framework of non-autocatalytic, intraholoenzyme reaction dynamics. A classification of switching characteristics of the system is made in the parameter space comprising the three controllable system parameters: an input-pulse intensity and initial concentrations of the two associated enzymes. It is found that a region of parameter space exists termed the transition zone, that exhibits a quasi-switching behaviour characterized by a signal storage time being prolonged by more than several orders of magnitude (10⁴ times in certain cases) for the increase of two orders of magnitude in the input signal intensity. The effect of alterations of certain rate constants on the quasi-switching property is explored. It is numerically demonstrated that the Ca²⁺/calmodulin-dependent kinase II-related phosphatase is the most important key enzyme for regulating the signal storage time. Received: 25 April 1994/Accepted in revised form: 16 December 1994     

High-performance liquid chromatographic determination of phospholipid peroxidation products of rat liver after carbon tetrachloride administration

A method to detect and determine phospholipid peroxidation products in a biological system was developed using reversed-phase high performance liquid chromatography and normal-phase HPLC. Reversed-phase HPLC could separate phosphatidylcholine (PC) hydroperoxides and phosphatidylethanolamine (PE) hydroperoxides of rat liver from the respective phospholipids. A linear relationship was observed between these hydroperoxides and their peak areas on the chromatogram. In the experiment with rats administered CCl4, reversed-phase HPLC gave prominent, large peaks attributable to the peroxidation of phospholipids, and the peroxide level of the liver phospholipids was tentatively determined. Normal-phase HPLC analysis confirmed that both PC and PE in the liver phospholipids were peroxidized after CCl4 treatment. Neither the thiobarbituric acid value of the liver homogenate nor the fatty acid composition of the liver phospholipid fraction showed any significant difference between CCl4-treated and control rats. It is concluded that normal-phase HPLC and reversed-phase HPLC can complement each other to serve as a direct and sensitive method for the determination of lipid peroxide levels in a biological source. However, it was difficult to distinguish phospholipid hydroperoxides from their hydroxy derivatives.     

GABA-ergic influence on the crossed extensor reflex

Intraventricular administration of muscimol (25–100 ng) and intravenously applied aminooxyacetic acid (2.5–10 mg/kg) depressed the crossed extensor reflex response in a dose-dependent manner. The inhibitory effects of both drugs were clearly antagonized by a subconvulsive dose of bicuculline. A very small dose of bicuculline (10–40 μg/kg, i.v.) produced a dose-related enhancement of the crossed extensor reflex response without any sign of convulsion. These results suggest that the crossed extensor reflex response is very sensitive to GABAergic drugs and central GABAergic mechanisms play a role in the modulation of the crossed extensor reflex response.     

Properties of a genetically reconstructed Prevotella ruminicola endoglucanase.

A pUC19-derived plasmid was constructed that coded for a hybrid cellulase with the Thermomonospora fusca E2 cellulose-binding domain at its C terminus joined to the Prevotella ruminicola 40.5-kDa carboxymethyl cellulase (CMCase). The hybrid enzyme was purified and characterized enzymatically. It bound tightly to cellulose, and its specific activities on carboxymethyl cellulose, amorphous cellulose, and ball-milled cellulose were 1.5, 10, and 8 times that of the 40.5-kDa CMCase, respectively. Furthermore, the modified enzyme gave synergism with an exocellulase in the degradation of filter paper, while the 40.5-kDa CMCase did not.     

Structural and functional modifications of the manganese cluster in Ca(2+)-depleted S1 and S2 states: electron paramagnetic resonance and X-ray absorption spectroscopy studies.

The effect of extraction of weakly bound Ca2+ by low-pH treatment on the O2-evolving apparatus was studied by use of low-temperature electron paramagnetic resonance (EPR) and X-ray absorption spectroscopy. In low-pH-treated PSII membranes, an S2 EPR multiline signal with modified line shape was induced by illumination at 0 degrees C, but its signal amplitude decreased upon lowering the excitation temperature with concomitant oxidation of cytochrome (cyt) b-559 in place of Mn. The half-inhibition temperature for formation of the modified multiline signal was found at -33 degrees C, which was much higher than that for formation of the normal S2 state in untreated control membranes. Signal IIf was normally induced down to -30 degrees C, but its dependence on excitation temperature was different from that for modified S2. This was interpreted as indicating that the low-temperature blockage of modified S2 formation is due to the incapability of electron abstraction from the Mn cluster. The Mn K-edge of X-ray absorption near-edge structure (XANES) spectrum shifted to lower energy by 0.8 eV after low-pH treatment, but the shift was reversed by addition of Ca2+. Upon illumination at 0 degrees C of treated membranes, the K-edge energy was up-shifted by 0.8 eV, but was not upon illumination at 210 K. These results were interpreted as indicating that extraction of weakly bound Ca2+ by low-pH treatment gives rise to structural and functional modulations of the Mn cluster.     

Purification and properties of extracellularβ-fructofuranosidases fromAureobasidium sp. ATCC 20524

Summary Two extracellular -fructofuranosidases (E-1 andE-2) fromAureobasidium sp. ATCC 20524, producing 1-kestose (1^F--fructofuranosyl-sucrose) from sucrose, were purified to homogeneity. Molecular weights of the enzymes were estimated to be about 304000 (E-1) and 315000 (E-2) Da by gel filtration. The enzymes contained 33% (w/w) (E-1) and 27% (w/w) (E-2) carbohydrate. TheK _m values for sucrose ofE-1 andE-2 andE-2 were 0.34 and 0.28 M, respectively. were 0.34 and 0.28 M, respectively. The enzymatic profiles of these enzymes were almost identical to intracellular enzymesP-1 andP-2 except for the differences in carbohydrate content andK _m values ofE-2 andP-2.     

Application of 15N-nuclear magnetic resonance (N.M.R.) spectroscopy for the study of nitrogen metabolism of a parasite: transamination in Angiostrongylus cantonensis eggs

In an attempt to study nitrogen metabolism in a parasite, we applied 15N-nuclear magnetic resonance (NMR) technology with a stable isotope, a 15N-labeled compound, for the study of the transamination system in A. cantonensis eggs, and demonstrated that 15N-aspartic acid can serve as an amino group donor for both the 2-oxoglutaric-glutamic acid and the pyruvic acid-alanine transamination systems in the eggs.     

Evidence for electron transfer via ubiquinone between quinoproteins D-glucose dehydrogenase and alcohol dehydrogenase of Gluconobacter suboxydans

Gluconobacter suboxydans contains membrane-bound D-glucose and alcohol dehydrogenases (GDH and ADH) as the primary dehydrogenases in the respiratory chain. These enzymes are known to be quinoproteins having pyrroloquinoline quinone as the prosthetic group. GDH reduces an artificial electron acceptor, ferricyanide, in the membrane, but not after solubilization with Triton X-100, while ADH can react with the electron acceptor even after solubilization and further purification. In this study, it has been shown that the ferricyanide reductase activity of GDH is restored by adding the supernatant solubilized with Triton X-100 to the residue, and also by incorporation of purified ADH into the membranes of an ADH-deficient strain. G. suboxydans var. alpha. In addition, the ferricyanide reductase activity of GDH was reconstituted in proteoliposomes from GDH, ADH, and ubiquinone-10. Thus, the results indicated that the electron transfer from GDH to ferricyanide was mediated by ubiquinone and ADH. The data also suggest that GDH and ADH transfer electrons mutually via ubiquinone in the respiratory chain.