Decoration of actin filaments with skeletal muscle heavy meromyosin containing either phosphorylated or dephosphorylated regulatory light chains

Heavy meromyosin containing almost intact regulatory light chains (LC2) was obtained from monomeric phosphorylated and dephosphorylated rabbit fast skeletal muscle myosin by brief chymotryptic digestion in the presence of CaCl2. Actin filaments, complexed with heavy meromyosin, display two different forms of arrowhead, depending on the form of LC2.     

Enhancement of Dissolution and Skin Permeability of Pentazocine by Proniosomes and Niosomal Gel

Proniosomes (PN) are the dry water-soluble carrier systems that may enhance the oral bioavailability, stability, and topical permeability of therapeutic agents. The low solubility and low oral bioavailability due to extensive first pass metabolism make Pentazocine as an ideal candidate for oral and topical sustained release delivery. The present study was aimed to formulate the PNs by quick slurry method that are converted to niosomes (liquid dispersion) by hydration, and subsequently formulated to semisolid niosomal gel. The PNs were found in spherical shape in the SEM and stable in the physicochemical and thermal analysis (FTIR, TGA, and XRD). The quick slurry method produced high recovery (>?80% yield) and better flow properties (θ?=?28.1–37.4°). After hydration, the niosomes exhibited desirable entrapment efficiency (44.45–76.23%), size (4.98–21.3 μm), and zeta potential (??9.81 to ??21.53 mV). The in vitro drug release (T_100%) was extended to more than three half-lives (2–4 h) and showed good fit to Fickian diffusion indicated by Korsmeyer-Peppas model (n?=?0.136–0.365 and R²?=?0.9747–0.9954). The permeation of niosomal gel was significantly enhanced across rabbit skin compared to the pure drug-derived gel. Therefore, the PNs are found promising candidates for oral as dissolution enhancement and sustained release for oral and topical delivery of pentazocine for the management of cancer pain.     

A model-dependent approach to correlate accelerated with real-time release from biodegradable microspheres

The purpose of this study was to determine the feasibility of applying accelerated in vitro release testing to correlate or predict long-term in vitro release of leuprolide poly(lactideco-glycolide) microspheres. Peptide release was studied using a dialysis technique at 37°C and at elevated temperatures (50°C–60°C) in 0.1 M phosphate buffered saline (PBS) pH 7.4 and 0.1 M acetate buffer pH 4.0. The data were analyzed using a modification, of the Weibull equation. Peptide release was temperature dependent and complete within 30 days at 37°C and 3 to 5 days at the elevated temperatures. In vitro release profiles at the elevated temperatures correlated well with release at 37°C. The shapes of the release profiles at all temperatures were similar. Using the modified Weibull equation, an increase in temperature was characterized by an increase in the model parameter, α, a scaling factor for the apparent rate constant. Complete release at 37°C was shortened from ∼30 days to 5 days at 50°C, 3.5 days at 55°C, 2.25 days at 60°C in PBS pH 7.4, and 3 days at 50°C in acetate buffer pH 4.0. Values for the model parameter β indicated that the shape of the release profiles at 55°C in PBS pH 7.4 (2.740) and 50°C in 0.1 M acetate buffer pH 4.0 (2.711) were similar to that at 37°C (2.577). The E_a for hydration and erosion were determined to be 42.3 and 19.4 kcal/mol, respectively. Polymer degradation was also temperature dependent and had an E_a of 31.6 kcal/mol. Short-term in vitro release studies offer the possibility of correlation with long-term release, thereby reducing the time and expense associated with longterm studies. Accelerated release methodology could be useful in the prediction of long-term release from extended release microsphere dosage forms and may serve as a quality control tool for the release of clinical or commercial batches. Selected for the 2005 AAPS Outstanding Graduate Student Research Award in Pharmaceutical Technologies Sponsored by Solvay Pharmaceuticals.     

Natural dead sea salt and retrospective dosimetry

Accidents resulting in widespread dispersal of radioactive materials have given rise to a need for materials that are convenient in allowing individual dose assessment. The present study examines natural Dead Sea salt adopted as a model thermoluminescence dosimetry system. Samples were prepared in two different forms, loose-raw and loose-ground, subsequently exposed to ⁶⁰Co gamma-rays, delivering doses in the range 2–10 Gy. Key thermoluminescence (TL) properties were examined, including glow curves, dose response, sensitivity, reproducibility and fading. Glow curves shapes were found to be independent of given dose, prominent TL peaks for the raw and ground samples appearing in the temperature ranges 361–385 ºC and 366–401 ºC, respectively. The deconvolution of glow curves has been undertaken using GlowFit, resulting in ten overlapping first-order kinetic glow peaks. For both sample forms, the integrated TL yield displays linearity of response with dose, the loose-raw salt showing some 2.5 × the sensitivity of the ground salt. The samples showed similar degrees of fading, with respective residual signals 28 days post-irradiation of 66% and 62% for the ground and raw forms respectively; conversely, confronted by light-induced fading the respective signal losses were 62% and 80%. The effective atomic number of the Dead Sea salt of 16.3 is comparable to that of TLD-200 (Z_eff 16.3), suitable as an environmental radiation monitor in accident situations but requiring careful calibration in the reconstruction of soft tissue dose (soft tissue Z_eff 7.2). Sample luminescence studies were carried out via Raman and Photoluminescence spectroscopy as well as X-ray diffraction, ionizing radiation dependent variation in lattice structure being found to influence TL response.

     

The phosphorylation-dephosphorylation process as a myosin-linked regulation of superprecipitation of fast skeletal muscle actomyosin

The dependence of the onset and course of turbidity changes ( superprecipitation) induced by ATP were studied in a natural actomyosin suspension with the dephosphorylated and phosphorylated forms of light chains (LC2) of myosin. It was found that the onset and time course of the changes in turbidity of the natural actomyosin suspension are strongly dependent on the (phosphorylated and dephosphorylated) form of these chains of myosin. The ATPase activity of actomyosin with phosphorylated LC2 was lower and the half-time for achieving maximal turbidity of actomyosin suspension after addition of ATP was higher than that of actomyosin with dephosphorylated LC2. Natural actomyosin preparations contain endogenous light-chain kinase and phosphatase. The changes of turbidity induced by ATP in the natural actomyosin suspension are greatly diminished in the presence of phosphate. Thiophosphorylation of LC2 of myosin leads to a decrease of the extent of superprecipitation of natural actomyosin. The release of [32P]phosphate from actomyosin containing [32P]ATP-phosphorylated LC2 of myosin increases with increased turbidity of actomyosin suspension. The change of the form LC2 as a kind of additional myosin-linked regulation of superprecipitation is discussed.     

The location of the thiol groups of myosin that are protected by pyrophosphate against reaction with 2,4-dinitrophenyl β-hydroxyethyl disulphide

Myosin modified in the presence or in the absence of pyrophosphate by 2,4-dinitrophenyl beta-hydroxyethyl disulphide was treated with iodo[1-(14)C]acetamide. The residual Ca(2+)-stimulated adenosine triphosphatase (ATPase) activity of the modified myosin was different depending on the presence or absence of PP(i) during modification and the number of 2,4-dinitrophenyl beta-hydroxyethyl disulphide-modified thiol groups. The radioactivity incorporated into the light components of myosin correlated with the Ca(2+)-stimulated ATPase activity of the modified myosin and decreased with decreasing residual Ca(2+)-stimulated ATPase activity of the modified myosin. When native myosin was treated with low concentrations of iodo[1-(14)C]acetamide the residual Ca(2+)-stimulated ATPase activity of carboxyamidomethylated myosin was high and the radioactivity incorporated into the light components of myosin was negligible. The thiol groups of the light components of myosin are essential to preserve the ATPase activity of the protein and are close to the pyrophosphate-binding sites.