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 28,634 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Bone mineral content (CMO, mg/cm2) was measured at the distal radius by dual photon absorptiometry (DPA, I125, Am241) in 1.161 women (w), aged 20-87 years. Women were subdivided into different groups according to the presence and duration of menopause. For gross evaluation of spinal osteoporosis (OP), the results of spinal X-rays were graded as follows: score 0: no signs of OP; score 1: aspecific signs of OP; score 2: typical signs of OP; score 3: wedging or collapse of one or more vertebrae. Women in postmenopausal state showed significantly reduced CMO (p less than .0005) when compared to women in premenopausal state; a significant correlation was found between CMO and years since menopause (p less than .0001). Concerning the relationship between CMO and spinal score, a progressive decreases in CMO from score 0 to score 3 was present and the correlation was significant (p less than .0001). In addition, women with score 3 showed a mean CMO below the "fracture threshold", in spite of the large overlap in individual CMO values. Our data suggest that radial DPA should be maintained as a "screening" procedure for OP.
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PMID:[Applications and results of photon absorptiometry]. 177 Sep 20

3,5-Dihydroxyphenylglycine is a crucial amino acid monomer in the nonribosomal glycopeptide antibiotic vancomycin. This nonproteinogenic amino acid is constructed from malonyl-CoA by a set of four enzymes, DpgA-D, in the biosynthetic cluster. DpgC is an unusual metal-free, cofactor-free enzyme that consumes O(2) during the conversion of 3,5-dihydroxyphenylacetyl-CoA (DPA-CoA) to the penultimate intermediate 3,5-dihydroxyphenylglyoxylate (DPGx). We show that in anaerobic incubations, DpgC catalyzes the exchange of the C(2)-methylene hydrogens of DPA-CoA at unequal rates, consistent with enzyme-mediated formation of the substrate-derived C(2)-carbanion as an early intermediate. Incubations with (18)O(2) reveal that DpgC transfers both atoms of an O(2) molecule to DPGx product. This establishes DpgC as a 1,2-dioxygenase that mediates thioester cleavage by the oxygen transfer process. These results are consistent with a DPA-CoA C(2)-peroxy intermediate, followed by enzyme-directed alpha-peroxylactone formation and collapse by O-O bond cleavage.
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PMID:DpgC is a metal- and cofactor-free 3,5-dihydroxyphenylacetyl-CoA 1,2-dioxygenase in the vancomycin biosynthetic pathway. 1538 Jan 80

The solvation and swelling behaviour of three dialkylaminoethyl methacrylate polymer brushes, of varying hydrophobicity, have been investigated using a combination of in situ ellipsometry and a quartz crystal microbalance with dissipation (QCM-D). At low pH the tertiary amine groups of the three polymers are protonated and all three brushes are significantly solvated and swell by adopting an extended conformation. As the pH is increased the weak polybasic brushes become increasingly deprotonated and collapse via solvent expulsion. By employing high temporal resolution measurements we have found that monomer hydrophobicity has a direct influence on the dynamics of this pH-response. The most hydrophobic poly(2-diisopropylamino)ethyl methacrylate (poly(DPA)) brush exhibits the fastest maximum swelling rate. This maximum swelling rate is reduced with decreasing monomer hydrophobicity for the 2-diethylamino, and even further for the 2-dimethylamino analogues. For all three brushes, the corresponding collapse transition is slower and compounded by an induction time that decreases with monomer hydrophobicity. Here also, the maximum collapse rate is greatest for the most hydrophobic polymer. This domination of the pH-response kinetics by monomer hydrophobicity is attributed to attractive hydrophobic forces between polymer segments overcoming the repulsive electrostatic forces between the tertiary amine residues.
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PMID:Hydrophobic effects within the dynamic pH-response of polybasic tertiary amine methacrylate brushes. 2555 78

The anion-specific solvation and conformational behavior of weakly basic poly(2-dimethylamino)ethyl methacrylate (poly(DMA)), poly(2-diethylamino)ethyl methacrylate (poly(DEA)), and poly(2-diisopropylamino)ethyl methacrylate (poly(DPA)) brushes, with correspondingly increasing inherent hydrophobicity, have been investigated using in situ ellipsometric and quartz crystal microbalance with dissipation (QCM-D) measurements. In the osmotic brush regime, as the initial low concentration of salt is increased, the brushes osmotically swell by the uptake of solvent as they become charged and the attractive hydrophobic inter- and intrachain interactions are overcome. With increased ionic strength, the brushes move into the salted brush regime where they desolvate and collapse as their electrostatic charge is screened. Here, as the brushes collapse, they transition to more uniform and rigid conformations, which dissipate less energy, than similarly solvated brushes at lower ionic strength. Significantly, in these distinct regimes brush behavior is not only ionic strength dependent but is also influenced by the nature of the added salt based on its position in the well-known Hofmeister or lyotropic series, with potassium acetate, nitrate, and thiocyanate investigated. The strongly kosmotropic acetate anions display low affinity for the hydrophobic polymers, and largely unscreened electrosteric repulsions allow the brushes to remain highly solvated at higher acetate concentrations. The mildly chaotropic nitrate and strongly chaotropic thiocyanate anions exhibit a polymer hydrophobicity-dependent affinity for the brushes. Increasing thiocyanate concentration causes the brushes to collapse at lower ionic strength than for the other two anions. This study of weak polybasic brushes demonstrates the importance of all ion, solvent, and polymer interactions.
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PMID:Anion-specific effects on the behavior of pH-sensitive polybasic brushes. 2576 82