(1/1549) Single cell studies of enzymatic hydrolysis of a tetramethylrhodamine labeled triglucoside in yeast.
Several hundred molecules of enzyme reaction products were detected in a single spheroplast from yeast cells incubated with a tetramethylrhodamine (TMR) labeled triglucoside, alpha-d-Glc(1-->2)alpha-d-Glc(1-->3)alpha-d-Glc-O(CH2)8CONHCH2- CH2NH- COTMR. Product detection was accomplished using capillary electrophoresis and laser induced fluorescence following the introduction of a single spheroplast into the separation capillary. The in vivo enzymatic hydrolysis of the TMR-trisaccharide involves at least two enzymes, limited by processing alpha-glucosidase I, producing TMR-disaccharide, TMR-monosaccharide, and the free TMR-linking arm. Hydrolysis was reduced by preincubation of the cells with the processing enzyme inhibitor castanospermine. Confocal laser scanning microscopy studies confirmed the uptake and internalization of fluorescent substrate. This single cell analysis methodology can be applied for the in vivo assay of any enzyme with a fluorescent substrate. (+info)
(2/1549) An improved method for the structural profiling of keratan sulfates: analysis of keratan sulfates from brain and ovarian tumors.
A previously developed method for the structural fingerprinting of keratan sulfates (Brown et al., Glycobiology, 5, 311-317, 1995) has been adapted for use with oligosaccharides fluorescently labeled with 2-aminobenzoic acid following keratanase II digestion. The oligosaccharides are separated by high-pH anion-exchange chromatography on a Dionex AS4A-SC column. This methodology permits quantitative analysis of labeled oligosaccharides which can be detected at the sub-nanogram ( approximately 100 fmol) level. Satisfactory calibration of this method can be achieved using commercial keratan sulfate standards. Keratan sulfates from porcine brain phosphocan and human ovarian tumors have been examined using this methodology, and their structural features are discussed. (+info)
(3/1549) Fluorimetric multiparameter cell assay at the single cell level fabricated by optical tweezers.
A fluorimetric multi-parameter cell sensor at the single cell level is presented which makes it possible to observe the physiological behavior of different cell lines, different physiological parameters, and statistical data at the same time. Different cell types were immobilized at predefined positions with high accuracy using optical tweezers and adhesion promoting surface layers. The process is applicable to both adherent and non-adherent cells. Coating of the immobilization area with mussel adhesive protein was shown to be essential for the process. Intracellular proton and calcium concentrations in different cell classes were simultaneously imaged and the specific activation of T lymphocytes was demonstrated. This method should be especially useful for drug screening due to the small sample volume and high information density. (+info)
(4/1549) Endometrial lysosomal enzyme activity in normal cycling endometrium.
The objective of this study was to evaluate the possible role of four lysosomal enzymes in endometrial function and remodelling during the normal menstrual cycle by fluorimetric measurement (acid phosphatase, N-acetyl-beta-D-glucosaminidase, alpha-L-fucosidase and alpha-D-mannosidase). A prospective study was conducted of 45 endometrial biopsies obtained from women with normal menstrual cycles. Activity of all four enzymes was identified in human endometrium. Activity of acid phosphatase and N-acetyl-beta-D-glucosaminidase was relatively high, whilst that of alpha-L-fucosidase and alpha-D-mannosidase was low. There was no significant change in the activity of any of the four enzymes from the proliferative to the secretory phase of the cycle. This study suggests that the activity of these enzymes remains constant throughout a major portion of the normal cycle. (+info)
(5/1549) Concatemerization of tRNA molecules in the presence of trivaline derivative.
The interaction of tRNA with trivaline dansyl hydrazide trifluoroacetate (DHTV) has been studied. The shape of curves of fluorimetric titration of tRNA with DHTV and vice versa can be explained only by formation of DHTV dimers on tRNA molecules, and subsequent association of DHTV-saturated tRNA molecules with each other. The ability of tRNA molecules to form concatemers in solution in the presence of DHTV has been demonstrated by electron microscopy. Electron microscopy of the tRNA-DHTV complexes stained with uranyl acetate revealed flexible rods 6-7 nm thick and up to several micrometers long. (+info)
(6/1549) Stopped-flow studies of the binding of 2-n-heptyl-4-hydroxyquinoline-N-oxide to fumarate reductase of Escherichia coli.
We have studied the kinetics of binding of the menaquinol analog 2-n-heptyl-4-hydroxyquinoline-N-oxide (HOQNO) by fumarate reductase (FrdABCD) using the stopped-flow method. The results show that the fluorescence of HOQNO is quenched when HOQNO binds to FrdABCD. The observed quenching of HOQNO fluorescence has two phases and it can be best fitted to a double exponential equation. A two-step equilibrium model is applied to describe the binding process in which HOQNO associates with FrdABCD by a fast bimolecular step to form a loosely bound complex; this is subsequently converted into a tightly bound complex by a slow unimolecular step. The rates of the forward and the reverse reactions for the first equilibrium (k1 and k2) are determined to be k1 = (1.1 +/- 0.1) x 10(7) M-1.s-1, and k2 = 6.0 +/- 0.6 s-1, respectively. The dissociation constants of the first equilibrium (Kd1 = k2/k1) is calculated to be about 550 nM. The overall dissociation constant for the two-step equilibrium, Kd overall = Kd1/[1+ (1/Kd2)], is estimated to be < or = 7 nM. Comparison of the kinetic parameters of HOQNO binding by FrdABCD and by dimethyl sulfoxide reductase provides important information on menaquinol binding by these two enzymes. (+info)
(7/1549) A new fluorescence-based, hydrophobic photolabeling technique for analyzing membrane-associated proteins.
We introduce a new, fluorescent and photoactivatable fatty acid derivative (SANU) for hydrophobic labelling of membrane-bound proteins. The technique allows fast and highly sensitive screening of hydrophobically inserting proteins analyzed by SDS-PAGE with a detection limit below 0.1 pmol. A reliable calculation of labelling efficiencies is achieved by simultaneous densitometry of fluorescence and protein staining. We have applied the new technique on the membrane inserting protein talin, G-actin, and, as a negative control, on RNase, which only binds electrostatically to negatively charged lipid interfaces. In several ways superior to radiolabelling, we can recommend this technique for all laboratories under any circumstances. (+info)
(8/1549) Significance of Na/Ca exchange for Ca2+ buffering and electrical activity in mouse pancreatic beta-cells.
We have combined the patch-clamp technique with microfluorimetry of the cytoplasmic Ca2+ concentration ([Ca2+]i) to characterize Na/Ca exchange in mouse beta-cells and to determine its importance for [Ca2+]i buffering and shaping of glucose-induced electrical activity. The exchanger contributes to Ca2+ removal at [Ca2+]i above 1 microM, where it accounts for >35% of the total removal rate. At lower [Ca2+]i, thapsigargin-sensitive Ca2+-ATPases constitute a major (70% at 0.8 microM [Ca2+]i) mechanism for Ca2+ removal. The beta-cell Na/Ca exchanger is electrogenic and has a stoichiometry of three Na+ for one Ca2+. The current arising from its operation reverses at approximately -20 mV (current inward at more negative voltages), has a conductance of 53 pS/pF (14 microM [Ca2+]i), and is abolished by removal of external Na+ or by intracellularly applied XIP (exchange inhibitory peptide). Inhibition of the exchanger results in shortening (50%) of the bursts of action potentials of glucose-stimulated beta-cells in intact islets and a slight (5 mV) hyperpolarization. Mathematical simulations suggest that the stimulatory action of glucose on beta-cell electrical activity may be accounted for in part by glucose-induced reduction of the cytoplasmic Na+ concentration with resultant activation of the exchanger. (+info)