Mass transfer in an airlift reactor with a net draft tube.

Gas-liquid mass transfer in an airlift reactor with net draft tube is investigated. The effects of both the ratio of draft tube to reactor diameter and the reactor pressure on oxygen transfer are considered. The value of the volumetric mass transfer coefficient, kLa, increases with a decreasing diameter ratio at higher air flow rates. The correlation of volumetric mass transfer coefficient with respect to the true superficial air velocity under different reactor pressures is determined. The kLa value decreases with increasing reactor pressure.     

Sugar transport by the bacterial phosphotransferase system. Fluorescence studies of subunit interactions of enzyme I

Enzyme I of the bacterial phosphoenolpyruvate:glycose phosphotransferase system (PTS) exhibits a temperature-dependent monomer/dimer equilibrium. The accompanying paper (Han, M. K., Roseman, S., and Brand, L. (1990) J. Biol. Chem. 265, 1985-1995) shows that the C-terminal -SH residue (Cys-575) can be modified specifically with fluorescent probes such as pyrene maleimide. The derivative retains full enzyme activity, and is capable of forming dimers at room temperature. In the present studies, Enzyme I labeled in this way is found to exhibit a temperature-, concentration-, and pH-dependent monomer/dimer association. The kinetics of dimer formation of Enzyme I is measured in the following way. A derivatized Enzyme I sample is prepared with a pyrene moiety irreversibly attached to the C-terminal -SH residue and 5,5'-dithiobis-2-nitrobenzoic acid reversibly attached to the other 3 -SH residues. This modified enzyme does not form dimers at room temperature. Addition of dithiothreitol results in total release of the thionitrobenzoate anion within 2 min. After the three -SH groups are unblocked, steady-state and nanosecond time-resolved emission anisotropy measurements indicate the dimer is formed over a period of 30 min. In a similar experiment, little dimer formation is observed at 3 degrees C, at temperature at which the native enzyme also does not form dimers. Tryptophan fluorescence is also examined during the release of the thionitrobenzoate. After the completion of thionitrobenzoate release, additional slow steady-state tryptophan fluorescence changes are observed. These results suggest that dimer formation may be preceded by a conformational change following thionitrobenzoate release.     

S-(N-methylcarbamoyl)glutathione: a reactive S-linked metabolite of methyl isocyanate

S-(N-methylcarbamoyl)glutathione, a chemically-reactive glutathione conjugate, has been isolated from the bile of rats administered methyl isocyanate and characterized, as its N-benzyloxycarbonyl dimethylester derivative, by tandem mass spectrometry. The ability of this glutathione adduct to donate an N-methylcarbamoyl moiety to the free -SH group of cysteine was evaluated in vitro with the aid of a highly specific thermospray LC/MS assay procedure. The glutathione adduct reacted readily with cysteine in buffered aqueous media (pH 7.4, 37 degrees C) and after 2 hr, 42.5% of the substrate existed in the form of S-(N-methylcarbamoyl)cysteine. The reverse reaction, i.e. between the cysteine adduct and free glutathione, also took place readily under these conditions. It is concluded that conjugation of methyl isocyanate with glutathione in vivo affords a reactive S-linked product which displays the potential to carbamoylate nucleophilic amino acids. The various systemic toxicities associated with exposure of animals or humans to methyl isocyanate could therefore be due to release of the isocyanate from its glutathione conjugate, which thus may serve as a vehicle for the transport of methyl isocyanate in vivo.     

Effect of gastric distention on RNA synthesis in neonatal chick liver.

RNA synthesis in the nuclei of liver from newly hatched chicks was enhanced 1.25 fold at 10 min after intragastric administration of water. Differential inhibition of RNA synthesis by alpha-amanitin indicated that the enhancement mainly represented rRNA synthesis; the synthesis of mRNA and tRNA was scarcely affected. Enhanced RNA synthesis was accompanied by greater susceptibility of nuclei to digestion by micrococcal nuclease, indicating that the chromatin structure was modified. It was further shown that the "water effect" was mimicked by distention of the stomach by raising the pressure in the intragastric balloon. Since the prior administration of atropine abolished the "water effect", the enhancement of hepatic RNA synthesis may be mediated by hepatic nervous system.     

Identification, characterization, and homologous up-regulation of latent (cryptic) receptors for tumor necrosis factor-alpha in rat liver plasma membranes

A population of latent (cryptic) receptors for tumor necrosis factor-alpha (TNF) has been characterized in the rat liver plasma membrane (PM). 125I-TNF bound to high (Kd = 1.51 +/- 0.35 nM) and low (Kd = 13.58 +/- 1.45 nM) affinity receptors in PM. Solubilization of PM with 1% Triton X-100 prior to incubation with 125I-TNF increased both high affinity (from 0.33 +/- 0.04 to 1.67 +/- 0.05 pmol/mg of protein) and low affinity (from 1.92 +/- 0.16 to 7.57 +/- 0.50 pmol/mg of protein) TNF binding without affecting the affinities for TNF. Digestion of intact PM with chymotrypsin abolished most of the TNF binding capacity of PM. However, substantial binding activity was recovered by solubilization of chymotrypsin-treated PM with 1% Triton X-100, suggesting the presence of a large latent pool of TNF receptors. The affinities of the high and low affinity sites recovered from chymotrypsin-treated membranes were similar to those of intact PM. Affinity labeling of receptors whether from PM, solubilized PM, or membranes digested with chymotrypsin and then solubilized resulted in cross-linking of 125I-TNF into Mr 130,000, 90,000, and 66,000 complexes. Thus, the properties of the latent TNF receptors were similar to those initially accessible to TNF. To determine if exposure of latent receptors is regulated by TNF, 125I-TNF binding to control and TNF-pretreated membranes was assayed. Specific binding was increased by pretreatment with TNF (p less than 0.05), demonstrating that hepatic PM contains latent TNF receptors whose exposure is promoted by TNF. Homologous up-regulation of TNF receptors may, in part, be responsible for sustained hepatic responsiveness during chronic exposure to TNF.     

氨基酸酯水解酶产生菌的筛选及其合成头孢立新的研究

From ten genera and 146 bacterial strains, 22 strains producing alpha-amino acid ester hydrolase were selected. Among them, AS 1.586 and 41-2 were the best. The optimal conditions for synthesis of cephalexin by pseudomonas aeruginosa 1.204 were investigated. The optimal pH and temperature for enzymatic synthesis reaction was pH 6.8 and 25 degrees C, respectively. By using 1% 7-ADCA, 3% PGME and 4% biomass, about 70% of 7-ADCA was converted to cephalexin under the mentioned conditions.     

Internally elongated rodent α-crystallin A chain: Resulting from incomplete RNA splicing?

αA^Ins, an elongated α-crystallin A chain previously observed in rat, was present beside the normal αA chain in mouse, gerbil and hamster, which places its origin at least 30 million years ago. Like in rat the sequences of golden hamster αA^Ins and αA were found to be identical, apart from the internal insertion of 22 residues in αA^Ins. The hamster chains only differed from the rat chains by a single substitution in the inserted sequence of αA^Ins. The origin of αA^Ins, by insertion of 22 residues in an otherwise unchanged αA chain, and its rigid evolutionary conservation are most easily explained by assuming the incomplete removal of a putative intervening sequence from the precursor mRNA of αA, leaving an intracistronic insert of 66 nucleotides in part of the eventually translated mRNA.     

Conservation of reference strains of Fusarium in pure culture

More than 300 reference strains representing 60 species and varieties ofFusarium cultures named according to different taxonomic systems are currently maintained at the American Type Culture Collection (ATCC). They have been preserved by freeze-drying and by freezing and subsequent storage in liquid nitrogen (–196°C) to insure their viability without contamination, variation, mutation, or deterioration. The materials and procedures used at the ATCC for the acquisition, accessioning, cataloguing, preservation and distribution are described. Longevity storage data for the strains available for distribution are presented and discussed.     

Oxidative phosphorylation in mitochondria isolated from small intestinal epithelium of thiamphenicol-treated rats and control rats

Treatment of rats with thiamphenicol in a dose of 125 mg/kg per day for 60–64 h causes specific inhibition of mitochondrial protein synthesis, leading to a drastic decrease of the cytochrome c oxidase activity in intestinal epithelium. At the same time the mitochondrial ATPase activity becomes resistant to inhibition by oligomycin. Experiments with isolated intestinal mitochondria revealed that respiration in state 3 is diminished by 55% with succinate (5 mM) and by 40% with pyruvate (10 mM) plus L-malate (2 mM) as the substrates, both as compared to intestinal mitochondria isolated from control rats. P : O ratios as well as respiratory control indices are comparable in the two groups of animals. Uncoupled respiration is inhibited by 35% with succinate as the substrate, while the succinate cytochrome c reductase activity remains unaltered. No inhibition of uncoupled respiration with pyruvate plus L-malate as the substrates was observed. The ATP-P_i exchange activity in the mitochondria from the treated animals is diminished by about 75%. It is concluded that in the mitochondria of the treated animals the inhibition of the coupled respiration (state 3) is caused by the limitation of the ATP-generating capacity and that electron transport is rate limiting only with the rapidly oxidized substrates such as succinate, if respiration is uncoupled.