Production of itaconic acid by Aspergillus terreus immobilized in polyacrylamide gels

Summary Living Aspergillus terreus cells were entrapped in polyacrylamide gels and employed in both replacement batch and continuous column reactors to produce itaconic acid from glucose.With the replacement batch reactor, maximum itaconic acid productivity was observed under the following conditions: pH 2.50, temperature at 35°C, addition of NH₄H₂PO₄ and MgSO₄·7H₂O. Using the continuous reactor, the maximum itaconic acid yield was 60 mg/h/40 g of gel. The biocatalyst activity or half-life was about 10 days.     

Down modulation of N-myc, heat-shock protein 70, and nucleolin during the differentiation of human neuroblastoma cells.

Cultured human neuroblastoma (GOTO) cells were induced to differentiate by dibutyryl cyclic AMP (Bt2cAMP) and/or retinoic acid (RA). A combination of Bt2cAMP (1 mM) and RA (1 microM) yielded the most significant networks of neurites after 3 to 4 days, this being associated with the reduction of N-myc mRNA levels. Next, we examined several cellular genes that were possibly linked with changes in N-myc gene expression under these conditions. Among the genes examined, both nucleolin and a major heat-shock protein (hsp70) mRNAs showed changes concomitant with those in N-myc mRNA levels when induced by Bt2cAMP and RA. Dibutyryl cAMP alone induced several short cellular processes and caused a marked decrease in N-myc mRNA within 2 days. RA alone induced a few long and straight neurites along the longitudinal axis of individual cells and a significant decrease in growth rate but showed neither network formation nor a decrease in N-myc gene expression. These results indicate differential effects of Bt2cAMP and RA on the regulatory mechanisms of both cell proliferation and differentiation and also indicate a possible association of expression of N-myc gene with those of hsp70 and nucleolin genes.     

Properties of recombinant cells capable of growing on serine without NhaB Na+/H+ antiporter in Escherichia coli.

Escherichia coli HIT-1 has a mutation in the Na+/H+ antiporter gene, nhaB (P. Thelen, T. Tsuchiya, and E. B. Goldberg, J. Bacteriol. 173:6553-6557, 1991). This strain is not able to utilize serine as a carbon source (T. Ishikawa, H. Hama, M. Tsuda, and T. Tsuchiya, J. Biol. Chem. 262:7443-7446, 1987), because an active NhaB is required to maintain the electrochemical potential of Na+, which drives serine transport via the Na+/serine carrier, the major transport system for serine. We isolated recombinant cells from a cross between strains HIT-1 and Hfr, and these cells were able to grow on serine even though the NhaB Na+/H+ antiporter of the recombinant cells was still defective. We found that the activity of the H+/serine cotransport system, one of the minor serine transport systems in E. coli, was elevated in the recombinant cells. H+/serine cotransport activity was induced by leucine in the recombinant cells more strongly than in strain HIT-1. A kinetic analysis showed that the Vmax, but not the Km, of the transport system was much higher in the recombinant cells than in strain HIT-1 cells.     

Dihydrofolate reductase as a new "affinity handle".

Dihydrofolate reductase (DHFR) has been demonstrated to be a versatile "affinity handle" for expression of recombinant proteins. The DHFR "handle" has advantages not only in terms of efficiency of expressing the fusion protein as a soluble form but also in stabilizing unstable polypeptides and facilitating purification of the expressed protein by means of methotrexate-bound affinity chromatography and by making use of the enzyme activity. Fifteen genes encoding different lengths of polypeptides of 5 to 44 amino acids were chemically synthesized and introduced into expression vectors, pTP70-1 or its derivatives. All the polypeptide genes were efficiently expressed in Escherichia coli cells as fusion proteins which show DHFR activity. The respective fusion proteins were highly purified from cell-free extracts by monitoring the DHFR activity at each purification step. The use of methotrexate-bound affinity chromatography was very effective. In order to cut out the polypeptides, the purified fusion proteins were treated with either BrCN or site-specific protease according to the spacer sequence. The objective polypeptide was purified by means of a reversed-phase high-pressure liquid chromatography (HPLC) system. Specific cleavage of the purified fusion protein actually yielded very few peptide fragments, so the assignment and isolation of the objective polypeptide were carried out without difficulty.     

Concanavalin A affects beta-tubulin mRNA expression during neuritic processes of mouse neuroblastoma N18TG2 cells in a different manner from colchicine

Addition of concanavalin A (Con A) to mouse neuroblastoma N18TG2 cells cultured with dibutyryl-cAMP which can stimulate neurite outgrowth, stopped the neuritic processes effectively. The extended neurites showed a gradual retraction for at least 8 hrs after addition of Con A, while addition of colchicine caused rapid retraction of the neurites. Immunocytochemistry showed that the addition of Con A did not disorganize the microtubules but the addition of colchicine did. The increase in beta-tubulin mRNA expression which was observed after cell culture and after stimulation by dB-cAMP was suppressed by the addition of Con A. Con A did not affect the beta-tubulin mRNA expression when the cells had already been cultured, while colchicine drastically decreased it. Thus, Con A appeared to affect the beta-tubulin mRNA expression in a different manner from colchicine, probably through inhibition of cell movement.     

Adrenal pheochromocytoma PC12h cells respond to pituitary adenylate cyclase activating polypeptide

An adrenal pheochromocytoma cell line, PC12h, was found to respond to a novel hypothalamic neuropeptide, Pituitary Adenylate Cyclase Activating Polypeptide (PACAP). The cells elevated both intracellular and extracellular cAMP levels on stimulation by PACAP, whereas they showed little response to VIP which is structurally related to PACAP. Using [125I]PACAP27 (a shorter form of the peptide) and [125I]VIP, we found large amounts of specific binding sites for PACAP but few binding sites for VIP in PC12h cells. These results indicate that PC12h cells respond to PACAP via a specific PACAP receptor.     

Suppression mutations in the defective beta subunit of F1-ATPase from Escherichia coli

The Escherichia coli mutant of the proton-translocating ATPase KF11 (Kanazawa, H., Horiuchi, Y., Takagi, M., Ishino, Y., and Futai, M. (1980) J. Biochem. (Tokyo) 88, 695-703) has a defective beta subunit with serine being replaced by phenylalanine at codon 174. Four suppression mutants (RE10, RE17, RE18, and RE20) from this strain capable of growth on minimal plate agar supplemented by succinate were isolated. The original point mutation at codon 174 was intact in these strains. Additional point mutations, Ala-295 to Thr, Gly-149 to Ser, Leu-400 to Gln, Ala-295 to Pro, for RE10, RE17, RE18, and RE20, respectively, were identified by the polymerase chain reaction and sequencing. These mutations, except for RE10, were confirmed as a single mutation conferring a suppressive phenotype by genetic suppression assay using KF11 as the host cells. The results indicated that Ser-174 has functional interaction with Gly-149, Ala-295, and Leu-400. The residues are located within the previously estimated catalytic domain of the beta subunit, indicating that this domain is indeed folded for the active site of catalytic function. Growth rates of the revertants in the minimal medium with succinate increased compared with that of KF11, showing that ATP synthesis recovered to some extent. The ATP hydrolytic activity in the revertant membranes increased in RE17 and RE20 but did not in RE10 and RE18, suggesting that synthesis and hydrolysis are not necessarily reversible in the proton-translocating ATPase (F1F0).     

Seroepizootiological survey on bluetongue virus infection in cattle in Japan

Bovine sera collected in various parts of Japan were subjected to seroepizootiological tests with bluetongue virus type 1 (BTV1), type 12 (BTV12), and type 20 (BTV20). All these viruses have been widely disseminated among cattle in the southern part of Japan in 1974. Relatively high incidences of neutralizing (NT) antibody against the three viruses were shown among cattle in the Kyushu district, including Okinawa Prefecture, or the southern part of Japan, but extremely low or incidences in Hokkaido, or the northern part of Japan. The incidence of reactors was higher in old animals. Cattle in Okinawa Prefecture showed a high rate of seroconversion for all the viruses during the summer of 1979. None of the animals seroconverted, however, manifested any sign of disease. Seroepizootiological investigation made it clear that BTV1, BTV12 and BTV20 had existed in Japan and that the epizootic of bluetongue virus infection started during a period from summer through early autumn.