Opposite behavior of two isozymes when refolding in the presence of non-ionic detergents.
(49/15061)
GroEL has a greater affinity for the mitochondrial isozyme (mAAT) of aspartate aminotransferase than for its cytosolic counterpart (cAAT) (Mattingly JR Jr, Iriarte A, Martinez-Carrion M, 1995, J Biol Chem 270:1138-1148), two proteins that share a high degree of sequence similarity and an almost identical spatial structure. The effect of detergents on the refolding of these large, dimeric isozymes parallels this difference in behavior. The presence of non-ionic detergents such as Triton X-100 or lubrol at concentrations above their critical micelle concentration (CMC) interferes with reactivation of mAAT unfolded in guanidinium chloride but increases the yield of cAAT refolding at low temperatures. The inhibitory effect of detergents on the reactivation of mAAT decreases progressively as the addition of detergents is delayed after starting the refolding reaction. The rate of disappearance of the species with affinity for binding detergents coincides with the slowest of the two rate-limiting steps detected in the refolding pathway of mAAT. Limited proteolysis studies indicate that the overall structure of the detergent-bound mAAT resembles that of the protein in a complex with GroEL. The mAAT folding intermediates trapped in the presence of detergents can resume reactivation either upon dilution of the detergent below its CMC or by adding beta-cyclodextrin. Thus, isolation of otherwise transient productive folding intermediates for further characterization is possible through the use of detergents. (+info)
Chemical transformations in individual ultrasmall biomimetic containers.
(50/15061)
Individual phospholipid vesicles, 1 to 5 micrometers in diameter, containing a single reagent or a complete reaction system, were immobilized with an infrared laser optical trap or by adhesion to modified borosilicate glass surfaces. Chemical transformations were initiated either by electroporation or by electrofusion, in each case through application of a short (10-microsecond), intense (20 to 50 kilovolts per centimeter) electric pulse delivered across ultramicroelectrodes. Product formation was monitored by far-field laser fluorescence microscopy. The ultrasmall characteristic of this reaction volume led to rapid diffusional mixing that permits the study of fast chemical kinetics. This technique is also well suited for the study of reaction dynamics of biological molecules within lipid-enclosed nanoenvironments that mimic cell membranes. (+info)
Kinetics of lactate and pyruvate transport in cultured rat myotubes.
(51/15061)
Skeletal muscle transport of lactate and pyruvate was studied in primary cultures of rat myotubes, applying the pH-sensitive fluorescent indicator 2', 7'-bis(carboxyethyl)-5(6)-carboxyfluorescein. The initial rate of decrease in intracellular pH (pHi) upon lactate or pyruvate incubation was used to determine total transport (carrier mediated and diffusion). Both lactate and pyruvate transport could be inhibited by a combination of 0.5 mM 4,4'-diisothiocyanostilbene-2, 2'-disulfonic acid, 5 mM mersalyl and 10 mM alpha-cyano-4-hydroxycinnamate. The kinetic parameters, Km and Vmax, for carrier-mediated transport of lactate were 9.9+/-1.1 mM and 0. 69+/-0.02 mmol l-1 s-1, respectively. For pyruvate, Km and Vmax were 4.4+/-1.3 mM and 0.30+/-0.05 mmol l-1 s-1, respectively. The diffusion component of the total transport was 0.0040+/-0.0005[S] (n=4) and 0.0048+/-0.0003[S] (n=4) for lactate and pyruvate, respectively. Furthermore, it was observed that the two monocarboxylate transporter isoforms present in mature skeletal muscles, MCT1 and MCT4 (formerly called MCT3 (M.C. Wilson, V.N. Jackson, C. Heddle, N.T. Price, H. Pilegaard, C. Juel, A. Bonen, I. Montgomery, O.F. Hutter, A.P. Halestrap, Lactic acid efflux from white skeletal muscle is catalyzed by the monocarboxylate transporter isoform MCT3, J. Biol. Chem. 273 (1998) 15920-15926)), were also expressed in primary culture of myotubes. (+info)
N-dansyl-S-nitrosohomocysteine a fluorescent probe for intracellular thiols and S-nitrosothiols.
(52/15061)
The fluorescence emission spectrum of N-dansyl-S-nitrosohomocysteine was enhanced approximately 8-fold upon removal of the NO group either by photolysis or by transnitrosation with free thiols like glutathione. The fluorescence enhancement was reversible in that it could be quenched in the presence of excess S-nitrosoglutathione. Attempts were then made to utilize N-dansyl-S-nitrosohomocysteine as an intracellular probe of thiols/S-nitrosothiols. Fluorescence microscopy of fibroblasts in culture indicated that intracellular N-dansyl-S-nitrosohomocysteine levels reached a maximum within 5 min. N-Dansyl-S-nitrosohomocysteine fluorescence was directly proportional to intracellular GSH levels, directly determined with HPLC. N-Dansyl-S-nitrosohomocysteine preloaded cells were also sensitive to S-nitrosoglutathione uptake as the intracellular fluorescence decreased as a function of time upon exposure to extracellular S-nitrosoglutathione. (+info)
Accurate measurement of avidin and streptavidin in crude biofluids with a new, optimized biotin-fluorescein conjugate.
(53/15061)
A new biotin-fluorescein conjugate with an ethylene diamine spacer was found to be the first fluorescent biotin derivative which truly mimicked d-biotin in terms of high affinity, fast association, and non-cooperative binding to avidin and streptavidin tetramers. These exceptional properties were attributed to the small size/length of the new ligand since all larger/longer biotin derivatives are known for their mutual steric hindrance and anti-cooperative binding in 4:1 complexes with avidin and streptavidin tetramers. Specific binding of the new biotin-fluorescein conjugate towards avidin and streptavidin was accompanied by 84-88% quenching of ligand fluorescence. In the accompanying study this effect was used for rapid estimation of avidin and streptavidin in a new 'single tube assay'. In the present study the strong quenching effect was utilized to accurately monitor stoichiometric titration of biotin-binding sites in samples with >/=200 pM avidin or streptavidin. The concentration was calculated from the consumption of fluorescent ligand up to the distinct breakpoint in the fluorescence titration profile which was marked by the abrupt appearance of strongly fluorescent ligands which were in excess. Due to this protocol the assay was not perturbed by background fluorescence or coloration in the unknown samples. The new fluorescence titration assay is particularly suited for quick checks on short notice because getting started only means to thaw an aliquot of a standardized stock solution of fluorescent ligand. No calibration is required for the individual assay and the ligand stock solution needs to be restandardized once per week (or once per year) when stored at -25 degrees C (or at -70 degrees C, respectively). (+info)
Rapid estimation of avidin and streptavidin by fluorescence quenching or fluorescence polarization.
(54/15061)
A new biotin-carboxyfluorescein conjugate has been presented in the accompanying study (G. Kada et al., Biochim. Biophys. Acta 000 (1999) 000-000) which contains ethylene diamine as a 4-atom spacer. This so-called biotin-4-fluorescein showed exceptionally fast and tight binding to avidin and streptavidin, and binding was accompanied by strong quenching. In the present study the specific quenching of 'biotin-4-fluorescein' was utilized to measure (strept)avidin concentrations (0.2-2 nM) by the extent of fluorescence quenching at 8 nM ligand concentration. Adsorption of (strept)avidin to the assay tubes was suppressed by inclusion of bovine serum albumin (0.1 mg/ml). Virtually the same specific response to avidin and streptavidin was also observed with commercial 'fluorescein-biotin', except that >10 h incubation times were required. The slow association of 'fluorescein-biotin' was attributed to the anti-cooperative binding which is due to the much longer spacer as compared to 'biotin-4-fluorescein'. The third ligand tested in this study was 'biotin-4-FITC' which was analogous to 'biotin-4-fluorescein' except that carboxyfluorescein was replaced by the fluorescein isothiocyanate residue. Surprisingly, this probe was much less quenched by avidin but this was compensated by an exceptionally high fluorescence polarization in the avidin-bound state. In conclusion, the new ligand 'biotin-4-fluorescein' appeared to be the most general and convenient probe: quenching was most pronounced and linearly dependent on (strept)avidin concentrations, the dose response for streptavidin was almost the same as for avidin, and the association kinetics were fast enough to reach equilibrium within 30 min incubation time. (+info)
Development of nuclear transfer and parthenogenetic rabbit embryos activated with inositol 1,4,5-trisphosphate.
(55/15061)
The present study was carried out to evaluate the effects of different activation protocols, enucleation methods, and culture media on the development of parthenogenetic and nuclear transfer (NT) rabbit embryos. Electroporation of 25 mM inositol 1,4, 5-trisphosphate (IP3) in calcium- and magnesium-free PBS immediately induced a single intracellular calcium transient in 6 out of 14 metaphase II-stage rabbit oocytes evaluated during a 10-min recording period. The percentage of oocytes treated with IP3 followed by 6-dimethylaminopurine (IP3 + DMAP) that cleaved (83.9%) and reached the blastocyst stage (50%) was significantly higher (p < 0.05) than those activated with multiple pulses (61.6% and 30.1%, respectively) or treated with ionomycin + DMAP (52.9% and 5.7%, respectively). Development of IP3 + DMAP-activated rabbit oocytes and in vivo-fertilized zygotes in different culture media was studied. Development of activated oocytes to the blastocyst stage in Earle's balanced salt solution (EBSS) supplemented with MEM nonessential amino acids, basal medium Eagle amino acids, 1 mM L-glutamine, 0.4 mM sodium pyruvate, and 10% fetal bovine serum (FBS) (EBSS-complete) (40.6%) was significantly higher (p < 0.05) than those that developed in either Dulbecco's Modified Eagle's medium (DMEM)/RPMI + 10% FBS (15.5%) or CR1aa + 10% FBS (4%) medium. In addition, 100% of in vivo-fertilized rabbit zygotes developed to the blastocyst stage in EBSS-complete. A third set of experiments was carried out to study the efficiency of blind versus stained (Hoechst 33342) enucleation of oocytes. Twenty-nine of 48 blind enucleated and IP3 + DMAP-activated oocytes cleaved (60.4%), and 15 (31.2%) subsequently reached the blastocyst stage, whereas 9 of 52 oocytes enucleated using epifluorescence (17.3%) cleaved, and none of these reached the blastocyst stage. When the above parameters that yielded the highest blastocysts were combined in an NT experiment using adult rabbit fibroblast nuclei, 72.2% (39 of 54) of the fused nuclear transplant embryos cleaved and 29.6% (16 of 54) reached the blastocyst stage. (+info)
Spermatid translocation in the rat seminiferous epithelium: coupling membrane trafficking machinery to a junction plaque.
(56/15061)
In this study, we demonstrate that specialized junction plaques that occur between Sertoli cells and spermatids in the rat testis support microtubule translocation in vitro. During spermatogenesis, Sertoli cells are attached to spermatids by specialized adhesion junctions termed ectoplasmic specializations (ESs). These structures consist of regions of the plasma membrane adherent to the spermatid head, a submembrane layer of tightly packed actin filaments, and an attached cistern of endoplasmic reticulum. It has been proposed that motor proteins on the endoplasmic reticulum interact with adjacent microtubules to translocate the junction plaques, and hence the attached spermatids, within the epithelium. If this hypothesis is true, then isolated junctions should support microtubule transport. To verify this prediction, we have mechanically isolated rat spermatids, together with their attached ESs, and tested them for their ability to transport microtubules in vitro. Most assays were done in the presence of 2 mg/ml testicular cytosol and at room temperature. ESs attached to spermatids supported microtubule translocation. In some cases in which motility events were detected, microtubules moved smoothly over the junction site. In others, the movement was slow but progressive, saltatory and "inch-worm-like." No motility was detected in the absence of exogenous ATP or in the presence of apyrase (an enzyme that catalyses the breakdown of ATP). Our results are consistent with the microtubule-based motility hypothesis of spermatid translocation. (+info)