A conserved epitope on nuclear pore phosphoproteins reflects cell division status

The nuclear pore complexes mediate the selective nuclear import of proteins in a signal- and energy-dependent process. We have earlier reported the characterization of a monoclonal antibody, Mab E2, that recognizes a novel class of nuclear pore phosphoproteins involved in signal-binding and protein transport. In the present study, we have analyzed the pattern of immunoreactivity of Mab E2 in cultured rat fibroblasts and have observed significant differences in the expression of epitopes in proliferating and quiescent cells. Furthermore, the common epitope recognized by Mab E2 is conserved across species, consistent with its essential role in nuclear protein import.

Inhibition of nuclear protein import by a monoclonal antibody against a novel class of nuclear pore proteins

Nuclear import of proteins is mediated by the nuclear pore complexes in the nuclear envelope and requires the presence of a nuclear localization signal (NLS) on the karyophilic protein. In this paper, we describe studies with a monoclonal antibody, Mab E2, which recognizes a class of nuclear pore proteins of 60-76 kDa with a common phosphorylated epitope on rat nuclear envelopes. The Mab E2-reactive proteins fractionated with the relatively insoluble pore complex-containing component of the envelope and gave a finely punctate pattern of nuclear staining in immunofluorescence assays. The antibody did not bind to any cytosolic proteins. Mab E2 inhibited the interaction of a simian virus 40 large T antigen NLS peptide with a specific 60-kDa NLS-binding protein from rat nuclear envelopes in photoaffinity labeling experiments. The antibody blocked the nuclear import of NLS-albumin conjugates in an in vitro nuclear transport assay with digitonin-permeabilized cells, but did not affect passive diffusion of a small non-nuclear protein, lysozyme, across the pore. Mab E2 may inhibit protein transport by directly interacting with the 60-kDa NLS-binding protein, thereby blocking signal-mediated nuclear import across the nuclear pore complex.

A quantitative immunostaining method for the measurement of UDP-galactose:lactosylceramide galactosyltransferase for the synthesis of globotriaosylceramide in rabbit small intestine and HeLa cells

Galactosyltransferase is required for the addition of galactose to lactosylceramide (galactose beta 1-4 glucose beta 1-1 ceramide), resulting in the synthesis of globotriaosylceramide (Gb3). We describe a quantitative more sensitive and specific method for the measurement of UDP-galactose:lactosylceramide galactosyltransferase activities in rabbit small intestine and HeLa cell which utilizes the specific binding of Shiga toxin to the product, Gb3. Intestinal microsomal or HeLa cell sonicate preparations were incubated in the presence of lactosylceramide and [14C]UDP-galactose. The lipid reaction products were extracted on C18 Bond-Elut columns, separated by high-performance thin-layer chromatography and exposed to Shiga toxin followed by polyclonal rabbit anti-Shiga toxin antibody and goat anti-rabbit IgG alkaline phosphatase conjugate. Gb3 was visualized with NBT and BCIP and quantitated by densitometry. These data were compared with a standard assay in which, following incubation and lipid extraction, radioactivity was measured by scintillation counting of the isolated lipids. There was a 22-fold increase in enzyme activity by the immunostaining method compared to the usual scintillation counting technique. This is attributable to the exclusion of radioactive lipids other than Gb3 in calculating enzyme activity and the correction for endogenous UDP-galactose. Thus, the immunostaining method provides increased accuracy, sensitivity, and specificity in the assay of galactosyltransferase activity.

Ultrasonic and thermodynamic studies of tetracyclines in solutions

The ultrasonic velocity, U, density, and viscosity of aqueous and non-aqueous (water + dioxan) solutions of tetracycline hydrochloride and chlorotetracycline have been measured at two different temperatures. Partial molal volumes, [Formula: see text] partial molal compressibility, [Formula: see text], Vand's interaction coefficients, Q and C, and thermodynamic activation parameters ΔG*, ΔS*, and ΔH* of these solutions have been computed from the ultrasonic velocity, density, and viscosity data. The results are interpreted in terms of solute–solvent interaction.

Effect of early iron deficiency in rat on the gamma-aminobutyric acid shunt in brain

Early iron deficiency in rat does not affect the weight or the protein, DNA, and RNA content but results in a slight reduction in gamma-aminobutyric acid (GABA) (13%, p less than 0.01) and glutamic acid (20%, p less than 0.001) content of the brain. The activities of the two GABA shunt enzymes, glutamate dehydrogenase and GABA-transaminase, and of the NAD+-linked isocitrate dehydrogenase (ICDH) were inhibited whereas the glutamic acid decarboxylase, mitochondrial NADP+-linked ICDH, and succinic dehydrogenase activities remained unaltered in brain. On rehabilitation with the iron-supplemented diet for 1 week, these decreased enzyme activities in brain attained the corresponding control values. However, the hepatic nonheme iron content increased to about 80% of the control, after rehabilitation for 2 weeks. A prolonged iron deficiency resulting in decreased levels of glutamate and GABA may lead to endocrinological, neurological, and behavioral alterations.