Solid state NMR study of [epsilon-13C]Lys-bacteriorhodopsin: Schiff base photoisomerization.

Previous solid state 13C-NMR studies of bacteriorhodopsin (bR) have inferred the C = N configuration of the retinal-lysine Schiff base linkage from the [14-13C]retinal chemical shift (1-3). Here we verify the interpretation of the [14-13C]-retinal data using the [epsilon-13C]lysine 216 resonance. The epsilon-Lys-216 chemical shifts in bR555 (48 ppm) and bR568 (53 ppm) are consistent with a C = N isomerization from syn in bR555 to anti in bR568. The M photointermediate was trapped at pH 10.0 and low temperatures by illumination of samples containing either 0.5 M guanidine-HCl or 0.1 M NaCl. In both preparations, the [epsilon-13C]Lys-216 resonance of M is 6 ppm downfield from that of bR568. This shift is attributed to deprotonation of the Schiff base nitrogen and is consistent with the idea that the M intermediate contains a C = N anti chromophore. M is the only intermediate trapped in the presence of 0.5 M guanidine-HCl, whereas a second species, X, is trapped in the presence of 0.1 M NaCl. The [epsilon-13C]Lys-216 resonance of X is coincident with the signal for bR568, indicating that X is either C = N anti and protonated or C = N syn and deprotonated.     

Experimental and computational characterization of mass transfer in high turndown bioreactors

Single-use bioreactors (SUBs, or disposable bioreactors) are extensively used for the clinical and commercial production of biologics. Despite widespread application, minimal results have been reported utilizing the turndown ratio; an operation mode where the working range of the bioreactor can be expanded to include low fluid volumes. In this work, a systematic investigation into free surface mass transfer and cell growth in high turndown single-use bioreactors is presented. This approach, which combines experimental mass transfer measurements with numerical simulation, deconvolutes the combined effects of headspace mixing and the free surface convective mass transfer on cell growth. Under optimized conditions, mass transfer across the interface alone may be sufficient to satisfy oxygen demands of the cell culture. Within the context of high turndown bioreactors, this finding provides a counterpoint to traditional sparge-based bioreactor operational philosophy. Multiple monoclonal antibody-producing cell lines grown using this high turndown approach showed similar viable cell densities to those cells expanded using a traditional cell bag rocker. Furthermore, cells taken directly from the turndown expansion and placed into production showed identical growth characteristics to traditionally expanded cultures. Taken together, these results suggest that the Xcellerex SUB can be run at a 5:1 working volume as a seed to itself, with no need for system modifications, potentially simplifying preculture operations.     

Prostaglandin H Synthetase-Mediated Metabolism of Dopamine: Implication for Parkinson's Disease

Abstract: Differences in prostaglandin H synthetase (PHS) activity in the substantia nigra of age- and post-mortem interval-matched parkinsonian, Alzheimer's, and normal control brain tissue were assessed. Prostaglandin E₂ (PGE₂, an index of PHS activity) was higher in substantia nigra of parkinsonian brain tissue than Alzheimer's or control tissue. Incubation of substantia nigra slices with arachidonic acid (AA) increased PGE₂ synthesis. Dopamine stimulated PHS synthesis of PGE₂. [³H]Dopamine was activated by PHS to electrophilic intermediate(s) that covalently bound to DNA, microtubulin protein, bovine serum albumin, and sulfhydryl reagents. When AA was replaced by hydrogen peroxide, PHS/H₂O₂-supported binding proceeded at rates similar to those observed with PHS/AA. Indomethacin and aspirin inhibited AA-mediated cooxidation of dopamine but not H₂O₂-mediated metabolism. PHS-mediated metabolism of dopamine was not affected by monoamine oxidase inhibitors. Substrate requirements and effects of specific inhibitors suggest cooxidation of dopamine is mediated by the hydroperoxidase activity of PHS. ³²P-postlabeling was used to detect dopamine-DNA adducts. PHS/AA activation of dopamine in the presence of DNA resulted in the formation of five dopamine-DNA adducts, i.e., 23, 43, 114, 70, and 270 amol/µg DNA. DNA adduct formation was PHS, AA, and dopamine dependent. PHS catalyzed cooxidation of dopamine in dopaminergic neuronal degeneration is discussed.     

Molecular organization of great millet (Sorghum vulgare) DNA

Approximately 52% of the nuclear genome of great millet(Sorghum vulgare) consists of repetitive DNA which can be grouped into very fast, fast and slow components. The reiteration frequencies of the fast and slow reassociating components are {dy7000} and 92 respectively. Approximately 90% of the genome consists of repeated sequences interspersed amongst themselves and with single copy sequences. The interspersed repeat sequences are of three sizesviz. > 1·5 kilobase pairs, 0·5–1·0 kilobase pairs and 0·15–0·30 kilobase pairs while the size of the single copy sequences is 3·0 kilobase pairs. Hence the genome organization of great millet is essentially of a mixed type NCL communication No. 3527.     

Consensus sequence for processing of peptide precursors at monobasic sites

Many regulatory peptide precursors undergo post-translational processing at mono- and/or dibasic residues. Comparison of amino acids around the monobasic cleavage sites suggests that these cleavages follow certain sequence motifs and can be described as the rules that govern monobasic cleavages: (i) a basic amino acid it present at either 3, 5, or 7 amino acids N-terminal to the cleavage site, (ii) hydrophobic aliphatic amino acids (leucine, isoleucine, valine, or methionine) are never present in the position C-terminal to the monobasic amino acid at the cleavage site, (iii) a cysteine is never present in the vicinity of the cleavage site, and (iv) an aromatic amino acid is never present at the position N-terminal to the monobasic amino acid at the cleavage site. In addition to these rules, the monobasic cleavages follow certain tendencies: (i) the amino acid at the cleavage site tends to be predominantly arginine, (ii) the amino acid at the position C-terminal to the cleavage site tends to be serine, alanine or glycine in more than 60% of the cases, (iii) the amino acid at either 3, 5, or 7 position N-terminal to the cleavage site tends to be arginine, (iv) aromatic amino acids are rare at the position C-terminal to the monobasic amino acid at the cleavage site, and (v) aliphatic amino acids tend to be in the two positions N-terminal to and the two positions C-terminal to the cleavage site, except as noted above. When compared with a large number of sequence containing single basic amino acids, these rules and tendencies are capable of not only correctly predicting the processing sites, but also are capable of excluding most of the single basic sequences that are known to be uncleaved. Many or these rules can also be applied to correctly predict the dibasic and multibasic cleavage sites suggesting that the rules and tendencies could govern endoproteolytic processing at the monobasic, dibasic and multibasic sites.     

Subcellular Localization, Partial Purification, and Characterization of a Dynorphin Processing Endopeptidase from Bovine Pituitary

An enzyme capable of cleaving dynorphin B-29 to dynorphin B-13 is present in bovine pituitary, with 40- to 50-fold higher specific activity in the posterior and intermediate lobes than in the anterior lobe. Subcellular fractionation of bovine neurointermediate pituitary shows that this enzyme is present in the peptide-containing secretory vesicles. The enzyme has been purified 2,800-fold from whole bovine pituitaries using ion-exchange and gel filtration chromatography. Purified dynorphin-converting enzyme has a neutral pH optimum, and is subsantially inhibited by the thiol-protease inhibitor p-chloromercuriphenylsulfonic acid, but not by serine or metalloprotease inhibitors. The purified enzyme processes dynorphin B-29 at Arg14, producing both dynorphin B-14 and dynorphin B-13 in a 5:1 ratio. No other cleavages are observed, suggesting that the activity is free from other proteases and is specific for single Arg sequences. Purified enzyme also processes dynorphin A-17 at the single Arg cleavage site, generating both dynorphin A-8 and A-9 in a 7:1 ratio. The tissue distribution, subcellular localization, and substrate specificity of this enzyme are consistent with a physiological role in the processing of dynorphin B-29 and dynorphin A-17, and possibly other peptides, at single Arg residues.     

Neue,abgewandelte pseudoguajanolide aus Psilostrophe villosa

Investigation of the North American species Psilostrophe villosa afforded, in addition to known compounds, five new sesquiterpene lactones, which all turn out to be modified pseudoguaianolides, most of them closely related to hymenolide. However, one of the lactones is a new type of nor-pseudoguaianolide. Furthermore a new monoacetylated borneol-β-D-glucoside is present. The chemotaxonomic situation is discussed briefly.     

Studies on hemolysis of human erythrocytes by linoleic acid

The results presented in this paper show that lysis of human erythrocytes by linoleic acid is not caused by peroxidation of the fatty acid. Peroxidase, superoxide dismutase and scavengers of O ₂ ⁻ and OH had no effect on the lysis while catalase showed only marginal inhibition suggesting that O ₂ ⁻ , OH, O ₂ ⁻ and H₂O₂ do not play any direct role in hemolysis by linoleic acid. Generators of H₂O₂ inhibited the lysis completely and methemoglobin cells were more resistant to hemolysis by linoleic acid. The fatty acid did neither bind to nor fomed complex with red cell ghosts. Membrane oxidation of sulphydryl groups was also not involved in the lysis. Β-Carotene, retinol and bile salts enhanced the lysis, while, cholesterol but not cholesterol acetate, inhibited it. Taurocholate-pretreated cells were more susceptible to linoleic acid lysis. These observations suggested-that lysis by linoleic acid may be due to its detergent property.