Radical copolymerization of N-vinyl-t-butylcarbamate

Summary The radical copolymerization of N-vinyl-tert-butylcarbamate (NVTBC) with styrene, methyl methacrylate, vinyl-pyrrolidone and 4-vinyl-pyridine was studied at 50–60° C in toluene, methanol or dioxane, using azo- bis- isobutyronitrile as the initiator. The reactivity ratios of the monomers were calculated from monomer feed and copolymers composition data using the Fineman-Ross method.The copolymers were hydrolysed in CH₃COOH/HCl mixtures at room temperature in order to obtain vinylamine containing copolymers. The extent of the solvolysis is dependent on the nature of the comonomer.The solvolysed copolymers bearing NH₂ groups were titrated by HCl in 2M NaCl medium in order to have more informations on the repartition of the NVTBC residues.     

Solution and solid state conformation of the human EGF receptor transmembrane region

The purpose of this article is to examine 10 steps analyzing the financial impact on a periodontal practice accepting a proposed managed care dental plan. It is emphasized that this analysis should be conducted before formally agreeing to accept the proposed plan. The procedures for examining the 10 steps include the use of hypothetical data for a periodontal practice confronted with a discounted fee plan. Each step is identified, discussed, and the hypothetical data are used to develop results presented in a set of tables. The steps in the analysis process include constructing a practice profit and loss statement and developing a dataset of practice characteristics and productivity measures. Other estimates should be made of covered lives, new patient utilization, existing patient utilization, utilization of non-covered services, estimating other sources of revenue and expense, and the impact on capacity utilization of operatories and practice staff. Results are presented in a set of analysis tables. The importance of multiple analyses is discussed as is the importance of analyzing the impact on results from changing assumptions. Some of the higher risk variables faced by the practitioner are identified for submission to risk evaluation to examine the sensitivity of results. Finally, the relationship between the proposed plan and the additional time required by the periodontist to meet the plan's specifications is examined in light of the data developed in the 10 steps and the results tables.     

Sequence-related behaviour of transmembrane domains from class I receptor tyrosine kinases

The purpose of this study was to investigate the effects of 316L stainless steel (SS) corrosion products on the in vitro biomineralization process, because tissue necrosis, bone loss, impaired bone mineralization, and loosening of orthopedic implants are associated with ions and debris resulting from biodegradation. Rat bone marrow cells were cultured in experimental conditions that favored the proliferation and differentiation of osteoblastic cells and were exposed to SS corrosion products obtained by electrochemical means for periods ranging from 1 to 21 days. Quantification of total and ionized Ca and P, as well as Fe, Cr, and Ni, ions in the culture media of control and metal added cultures during the incubation period was performed to study the influence of corrosion products on the Ca and P consumption that occurs during the mineralization process. Control cultures and metal effects on cultures were evaluated concerning DNA content, enzymatic reduction of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), and alkaline phosphatase (ALP) activity. Histochemical detection of ALP, Ca, and phosphate deposition, and examination of the cultures by scanning and transmission electron microscopy (SEM and TEM) were also performed. The presence of SS corrosion products resulted in impairment of the normal behavior of rat bone marrow cultures. Levels of Cr and Ni in the medium of cultures exposed to 316L SS corrosion products decreased throughout the incubation period, suggesting a regular deposition of these species; these results were supported by TEM observation of the cultures. Cultures exposed to the corrosion products presented lower DNA content, MTT reduction, and ALP activity and failed to form mineralized areas. These cultures showed negative staining on histochemical reactions for the identification of calcium and phosphate deposition and SEM and TEM examination did not show mineral globular structures or mineralization foci, respectively, which is characteristic of cultures grown in control conditions. These results suggest that metal ions associated with 316L SS are toxic to osteogenic cells, affecting their proliferation and differentiation.     

Skeletal muscle of a growing organism has a greater transformation after electrical stimulation than adult skeletal muscle

Six adult sheep and four newborn lambs (5 days old) were implanted with stimulator leads into the latissimus dorsi muscle and connected to a Myostim 7220 pacing system (Telectronics Pacing Systems, Inc., Englewood, CO). Electrical stimulation was started immediately after the operation. After 8 weeks of electrical stimulation, contractile force (CF) in adult sheep decreased to 76-81%, and to 78-82% in lambs. After 2 weeks' delay, CF in adults was 96-98%, and only 89-93% in lambs. After a 30 min intensive stress test, unconditioned control muscle lost 39% in lambs and 43% in adults. Muscle conditioned for 8 weeks lost 7-8% CF. However, after 2 weeks' delay, CF in adult muscle lost 33%, but only 12% in lambs. After cessation of electrical stimulation, the LDH-5 and LDH-1 + 2 fractions reverted to initial levels in adults, whereas in lambs, these levels continued to follow trends established during electrical stimulation. In both adults and lambs, the percent area occupied by the mitochondria increased during electrical stimulation by 6.9% in adults and 6.5% in lambs. After electrical stimulation cessation, the percent area in adults returned to baseline levels, whereas it continued to be elevated in lambs (3.3% vs 5.1%, respectively). The transformed muscle of the lamb did not revert to baseline levels after a delay period.     

Purification and characterization of a soluble form of mammalian adenylyl cyclase

An engineered, soluble form of mammalian adenylyl cyclase has been expressed in Escherichia coli and purified by three chromatographic steps. The enzyme utilizes one molecule of ATP to synthesize one molecule of cyclic AMP and pyrophosphate at a maximal specific activity of 12.8 micromol/min/mg, corresponding to a turnover number of 720 min-1. Although devoid of membrane spans, the enzyme displays all of the regulatory properties that are common to mammalian adenylyl cyclases. It is activated synergistically by Gsalpha and forskolin and is inhibited by adenosine (P-site) analogs with kinetic patterns that are identical to those displayed by the native enzymes. The purified enzyme is also inhibited directly by the G protein betagamma subunit complex. After adenovirus-mediated expression in adenylyl cyclase-deficient HC-1 cells, the enzyme can be stimulated synergistically by Gs-coupled receptors and forskolin.