Analysis of the loop-helix interaction in bundle motif protein structures

Molecular dynamics simulations and energy analysis have been carried out to study the structural mobility and stability of the four -helix bundle motifs. The simulation results as well as the X-ray data show that the atomic RMS fluctuation is larger at the loop region for four representative proteins investigated: methemerythrin, cytochrome b-562, cytochrome c, and bovine somatotropin. The loop-loop, helix-helix, and loop-helix interactions are computed for the unfolded and folded proteins. In the folded and solvated protein structures the loop-helix interaction is stronger than the helix-helix interaction, especially in the electrostatic component. But the stabilization energies of both the loop-helix and the helix-helix interactions relative to the those of an unfolded structure are of the same order of magnitude. The stabilization due to protein-solvent interaction is greater in the helix region than in the loop region. The percentage of hydrophilic solvent accessible area for the four proteins studied was calculated with the method of Eisenberg and McLachlan. The percentage of the hydrophilic area is greater in the loops than in the helices. A Poisson-Boltzmann calculation shows that the potential from the loops acting on a helix is generally more negative than that from other helices.     

Theoretical and experimental determination of SAR patterns for spherical tissue models in a rectangular resonant cavity

Specific absorption rates (SARs) were determined theoretically and experimentally for several spherical models of tissue exposed to electrical fields of TE101 mode in a rectangular cavity of 57.3 MHz resonant frequency. The approximate theoretical SAR can be calculated according to the Mie theory by superposition of four plane waves representing the fields excited in the cavity. The theoretical and thermographically determined SAR patterns in spheres with radii of 5, 7.5, and 10 cm and with conductivities of 0.1, 1, and 10 S/m were compared. For a sphere with radius less than 7.5 cm and conductivity less than 1 S/m, the SAR was quite uniform. When conductivity was increased to 10 S/m, the SAR patterns showed higher absorption in the periphery of the largest sphere (10-cm radius). These characteristics are important in evaluating the scaling technique of exposing a model of a human to very-high-frequency fields to obtain power absorption data in humans exposed to high-frequency or very-low-frequency fields.     

SAR in rats exposed in 2,450-MHz circularly polarized waveguides

Average specific absorption rates (SARs) for live rats exposed in 2,450-MHz circularly polarized waveguides were estimated from the total system loss determined from measurements using five power meters, and a correction factor representing actual SAR/apparent SAR. The actual SAR was measured by twin-well calorimetry and the apparent SAR by power meters. Values were obtained for carcasses of various body masses for five orientations. The average SAR with free movement in the cages changed less than threefold as the rats grew from 200 to 700 g. The ratio of peak to average SAR in the body was less than 3. These results indicate relatively constant energy disposition in rats exposed in the circularly polarized waveguide.     

Regulation of the synthesis of human chorionic gonadotropin by strains of HeLa cells in culture

Summary Thirty-seven strains of HeLa cells were examined for their ability to synthesize human chorionic gonadotropin (hCG) and its alpha subunit (hCG-α) in culture. Synthesis of hCG-α and hCG also was investigated in the presence of sodium butyrate and 5-bromo-2′-deoxyuridine (BrdUrd). All HeLa strains synthesized hCG-α in culture. Sodium butyrate increased the synthesis of hCG-α in all HeLa cells; BrdUrd increased synthesis in 32 of the 37 strains examined. Although few HeLa strains synthesized hCG in the absence of inducers, hCG was detected in most strains in the presence of sodium butyrate. The synthesis of hCG and its alpha subunit is, therefore, a stable genetic characteristics of HeLa cells. Certain preparations of hCG and its subunits were generously provided through the Center for Population Research of the National Institute of Child Health and Human Development, NIH.     

Modifications of myelin basic protein which occur during its isolation.

Abstract— Chromatography of myelin basic protein (BP) on carboxymethylcellulose gives a pattern of multiple components, of which three are major. Component 1 is considered the unmodified species of BP while component 2 has been found to be modified primarily by deamidation and component 3 by phosphorylation (Chou et al., 1976). ³ 3 The numbering system for the components is that used by DEIBLER & MARTENSON (1973) for guinea pig BP and is preferred over the reverse system of numbering used by CHOU et al. (1976); i.e. components 1, 2 and 3 of DEIBLER & MARTENSON (1973) are the same as components 6, 5 and 4 of CHOU et al. (1976), respectively.
In contrast to BP prepared from tissue delipidated in the standard fashion in chloroform–methanol (CM powder), BP prepared from tissue delipidated first in acetone and then in chloroform–methanol (ACM powder) gave an elution pattern on carboxymethylcellulose characterized by a decrease in component 1 and an increase in the earlier eluting, less basic components. Studies with radiolabelled component 1 showed that this difference in elution patterns was due to the partial conversion of component 1 to less basic components during the extraction of ACM powder at neutral pH. The components derived from component 1 (D2, D3 and D4) were then isolated and subjected to tryptic peptide map analyses and determination of their carboxy-terminal arginine content and content of phosphorus. None of the derived components contained phosphorus but tryptic peptide map analyses did show the presence of two minor peptides, T14M₂ and T20M, previously found in component 2 from CM powder and considered to be the deamidation products of their parent peptides T14 and T20 (Chou et al., 1976). In addition components D3 and D4 were shown to have lost appreciable arginine from their carboxy-termini. Since none of the efforts to reduce enzyme activity in vitro had any appreciable effect on components 2 and 3 it was concluded that phosphorylation probably occurs exclusively in vivo, that deamidation occurs both in vivo and in vitro and that loss of carboxy-terminal arginine occurs exclusively in vitro.     

Induction of placental alkaline phosphatase in choriocarcinoma cells by 5-bromo-2′-deoxyuridine

Summary Growth of choriocarcinoma cells in the presence of 5-bromo-2′-deoxyuridine (BrdUrd) results in a 30- to 40-fold increase in alkaline phosphatase activity. The effect of BrdUrd is specific for phosphatase with an alkaline pH optimum. The induction by BrdUrd is probably not due to the production of an altered enzyme, since the induced enzyme resembles the basal enzyme in thermal denaturation and kinetic properties. Enzyme induction can be prevented by thymidine but not by deoxycytidine or deoxyuridine. The induction of alkaline phosphatase appears to require incorporation of the BrdUrd into cellular DNA. The presence of BrdUrd in the growth medium is not necessary for alkaline phosphatase induction in proliferating cells containing: BrdUrd-substituted genomes. However, enzyme induction and maintenance of the induced levels of alkaline phosphatase in nonproliferating cells containing BrdUrd-substituted DNA requires the presence of the analogues in the medium. The induction of alkaline phosphatase by BrdUrd in probably an indirect process.     

Expression and regulation of UDP-glucuronate: neolactotetraosylceramide glucuronyltransferase in the nervous system

Sulfoglucuronyl glycolipids (SGGLs) are temporally and spatially regulated molecules present in the nervous system during its development. The characteristics of the rat brain enzyme glucuronyltransferase involved in the biosynthesis of SGGLs have been described. The enzyme catalyzes the transfer of glucuronic acid (GlcA) from UDP-GlcA to terminal galactose of the neolacto (type 2) series of glycolipids to form beta 1-3-linked glucuronyl neolacto glycolipids. The enzyme was highly specific for the neolacto series of acceptor glycolipids, neolactotetraosylceramide (nLcOse4Cer), neolactohexaosylceramide (nLcOse6-Cer), and neolactooctaosylceramide (nLcOse8Cer) and was different from the drug-inducible phenol:GlcA transferase. Considerable activity of GlcA transferase was present in the adult rat cerebral cortex, even though SGGLs almost completely disappeared from the cortex by postnatal day 15. In the cerebellum, although levels of SGGLs increased with development, the specific activity of GlcA transferase declined. The results indicated that GlcA transferase was not a regulatory enzyme controlling the expression of SGGLs. Measurements of the levels of nLcOse4Cer and nLcOse6Cer in these neural tissues indicated that the availability of these precursors may regulate the differential expression of SGGLs seen previously. GlcA transferase was significantly reduced in the cerebellar Purkinje cell degenerating murine mutant (pcd/pcd), which is consistent with the loss of SGGLs in the cerebellum of this mutant and specific association of these glycolipids with Purkinje cells.