Enhancement of penicillin acylase activity by cultivating immobilized Kluyvera citrophila

Summary Whole cells of Kluyvera citrophila were immobilized in polyacrylamide gel. The penicillin acylase activity of immobilized whole cells was 60%–70% of native cells. When the immobilized cells were continuously cultivated for 40 h in an aerated fermentor containing peptone medium and were treated with alkali in order to remove -lactamase activity, the immobilized cells produced ampicillin up to 4.4 times faster than noncultivated cells.Ampicillin production was investigated in a column system using these cultivated immobilized whole cells. The cultivated immobilized cells showed excellent performance in continuous ampicillin production.     

Molecular nature of the calcium-dependent cell-cell adhesion system in mouse teratocarcinoma and embryonic cells studied with a monoclonal antibody

The molecular nature of the Ca2+-dependent cell-cell adhesion system in mouse teratocarcinoma (t-CDS) was studied using a monoclonal antibody recognizing t-CDS. We isolated a hybridoma clone producing a monoclonal antibody (ECCD-1) able to disrupt cell-cell adhesion when added to monolayer cultures of teratocarcinoma cells. This antibody bound to the cells with intact t-CDS, resulting in an inhibition of their aggregation, but did not bind to cells from which t-CDS was removed by trypsin treatment in the absence of Ca2+. The binding of ECCD-1 to cell surfaces required Ca2+ but not other ions. Western blot analysis showed that ECCD-1 recognizes multiple cell surface proteins, the major one of which is a component with a molecular weight of 124,000. The binding of ECCD-1 to these antigens was Ca2+-dependent even in cell-free systems, suggesting that the molecules involved in t-CDS undergo conformational changes by binding with Ca2+, leading to conversion of their molecular structure into an active form. ECCD-1 also reacted with 8-cell stage mouse embryos and with certain types of epithelial cells (excluding fibroblastic cells) in various differentiated tissues collected from mouse fetuses, again affecting their cell-cell adhesion. We also showed that a monoclonal antibody (DE1) raised against gp84 (F. Hyafil et al., 1981, Cell 26, 447-454) recognizes the same antigens as ECCD-1.     

Identification of the active site in penicillin-binding protein 3 of Escherichia coli.

We report the sequence of the active site tryptic peptide of penicillin-binding protein 3 from Escherichia coli. Purified penicillin-binding protein 3 was labeled with [14C]penicillin G and digested with trypsin, and the resulting radioactive peptides were isolated by a combination of gel filtration and high-pressure liquid chromatography. The major radioactive peak from high-pressure liquid chromatography was sequenced, and the peptide Thr-Ile-Thr-Asp-Val-Phe-Glu-Pro-Gly-Ser-Thr-Val-Lys, which comprises residues 298 to 310 in the amino acid sequence, was identified. This sequence is compared with the active site sequences from other penicillin-binding proteins and beta-lactamases.     

Role of the loop structure of the catalytic domain in rice class I chitinase

In the three-dimensional structure of a rice class I chitinase (OsChia1b) determined recently, a loop structure (loop II) is located at the end of the substrate-binding cleft, and is thus suggested to be involved in substrate binding. In order to test this assumption, deletion of the loop II region from the catalytic domain of OsChia1b and replacement of Trp159 in loop II with Ala were carried out. The loop II deletion and the W159A mutation increased hydrolytic activity not only towards (GlcNAc)6 but also towards polysaccharide substrates. Similar results were obtained for kcat/Km values determined for substrate reduced-(GlcNAc)5. The two mutations shifted the splitting positions in (GlcNAc)6 to the reducing end side, but the shift was less intensive in the Trp mutant. Theoretical analysis of the reaction time course indicated that sugar residue affinity at the +3 subsite was reduced from -2 kcal/mol to +0.5 kcal/mol by loop II deletion. Reduced affinity at the +3 subsite might enhance the release of product fragments, resulting in higher turnover and higher enzymatic activities. Thus, we concluded that loop II is involved in sugar residue binding at the +3 subsite, but that Trp159 itself appears to contribute only partly to sugar residue interaction at the subsite.     

Establishment of the comet assay in the freshwater snail Biomphalaria glabrata (Say, 1818)

The single cell gel electrophoresis or the comet assay was established in the freshwater snail Biomphalaria glabrata. For detecting DNA damage in circulating hemocytes, adult snails were irradiated with single doses of 2.5, 5, 10 and 20 Gy of (60)Co gamma radiation. Genotoxic effect of ionizing radiation was detected at all doses as a dose-related increase in DNA migration. Comet assay in B. glabrata demonstrated to be a simple, fast and reliable tool in the evaluation of genotoxic effects of environmental mutagens.     

Effect of menstrual cycle phase on the ventilatory response to rising body temperature during exercise

To examine the effect of menstrual cycle on the ventilatory sensitivity to rising body temperature, ten healthy women exercised for ~60 min on a cycle ergometer at 50% of peak oxygen uptake during the follicular and luteal phases of their cycle. Esophageal temperature, mean skin temperature, mean body temperature, minute ventilation, and tidal volume were all significantly higher at baseline and during exercise in the luteal phase than the follicular phase. On the other hand, end-tidal partial pressure of carbon dioxide was significantly lower during exercise in the luteal phase than the follicular phase. Plotting ventilatory parameters against esophageal temperature revealed there to be no significant menstrual cycle-related differences in the slopes or intercepts of the regression lines, although minute ventilation and tidal volume did significantly differ during exercise with mild hyperthermia. To evaluate the cutaneous vasodilatory response, relative laser-Doppler flowmetry values were plotted against mean body temperature, which revealed that the mean body temperature threshold for cutaneous vasodilation was significantly higher in the luteal phase than the follicular phase, but there were no significant differences in the sensitivity or peak values. These results suggest that the menstrual cycle phase influences the cutaneous vasodilatory response during exercise and the ventilatory response at rest and during exercise with mild hyperthermia, but it does not influence ventilatory responses during exercise with moderate hyperthermia.     

Simple and tunable Förster resonance energy transfer-based bioprobes for high-throughput monitoring of caspase-3 activation in living cells by using flow cytometry

Sensing systems based on F?rster resonance energy transfer (FRET) can be used to monitor enzymatic reactions, protein-protein interactions, changes in conformation, and Ca2+ oscillations in studies on cellular dynamics. We developed a series of FRET-based chimeric bioprobes, each consisting of fluorescent protein attached to a fluorescent dye. Green and red fluorescent proteins were used as donors and a series of Alexa Fluor dyes was used as acceptors. The basic fluorescent proteins were substituted with appropriate amino acids for recognition of the target (caspase-3) and subjected to site-directed modification with a fluorescent dye. Variants that retained similar emission profiles to the parent proteins were readily derived for use as FRET-based bioprobes with various fluorescent patterns by incorporating various fluorescent proteins and dyes, the nature of which could be adjusted to experimental requirements. All the constructs prepared functioned as bioprobes for quantitative measurement of caspase-3 activity in vitro. Introduction of the bioprobes into cells was so simple and efficient that activation of caspase-3 upon apoptosis could be monitored by means of cytometric analysis. FRET-based bioprobes are valuable tool for high-throughput flow-cytometric analysis of many cellular events when used in conjunction with other fluorescent labels or markers. Statistical dynamic studies on living cells could provide indications of paracrine signaling.     

Alterations in renal iron metabolism caused by a copper/zinc-superoxide dismutase deficiency

Copper/zinc-superoxide dismutase knockout (SOD1 KO) mice have been extensively used as an experimental animal model of pathology associated with oxidative stress. The mice spontaneously develop mild chronic hemolytic anaemia (HA). We previously reported that the kidneys of these types of mice contain massive amounts of iron. In this study, to clarify the role of the kidney for iron metabolism under HA, changes in the levels of expression and functions of iron-related proteins were examined. In SOD1 KO mice kidneys, protein levels of iron transporters, the iron-responsive element (IRE)-binding activity of IRP1 and the levels of phosphorylation of IRP1 are all increased. These findings indicate that oxidative stress caused by a SOD1 deficiency probably enhances the phosphorylation of and the conversion of IRP1 to the IRE-binding form, which may accelerate the reabsorption of iron by renal tubular cells. Kidney could play an important role in iron homeostasis under conditions of HA.     

Functional analysis of the Notch ligand Jagged1 missense mutant proteins underlying Alagille syndrome

Heterozygous mutations in the JAG1 gene, encoding Notch ligand Jagged1, cause Alagille syndrome (ALGS). As most of the mutations are nonsense or frameshift mutations producing inactive truncated proteins, haplo-insufficiency is considered the major pathogenic mechanism of ALGS. However, the molecular mechanisms by which the missense mutations cause ALGS remain unclear. Here we analyzed the functional properties of four ALGS missense mutant proteins, P163L, R184H, G386R and C714Y, using transfected mammalian cells. P163L and R184H showed Notch-binding activities similar to that of the wild-type when assessed by immunoprecipitation. However, their trans-activation and cis-inhibition activities were almost completely impaired. These mutant proteins localized mainly to the endoplasmic reticulum (ER), suggesting that the mutations induced improper protein folding. Furthermore, the mutant proteins bound more strongly to the ER chaperone proteins calnexin and calreticulin than the wild-type did. C714Y also localized to the ER, but possessed significant trans-activation activity and lacked enhanced binding to the chaperones, indicating a less severe phenotype. The properties of G386R were the same as those of the wild-type. Dominant-negative effects were not detected for any mutant protein. These results indicate that accumulation in the ER and binding to the chaperones correlate with the impaired signal-transduction activities of the missense mutant proteins, which may contribute to the pathogenic mechanism of ALGS. Our findings, which suggest the requirement for cell-surface localization of Jagged1 for cis-inhibition activities, also provide important information for understanding the molecular basis of Notch-signaling pathways.