Utilization of phosphate diester by the marine diatom Chaetoceros ceratosporus

Utilization of phosphate diester (PDE) and phosphodiesterase(PDEase) production by five marine phytoplankton species wereexamined in the laboratory to evaluate the contribution of PDEto the growth of phytoplankton. Among the five marine phytoplanktonspecies tested, only Chaetoceros ceratosporus was able to usethe PDE compound, bis(p-nitrophenyl) phosphate (bis-NPP), effectivelyas a sole phosphorus source. In addition, C. ceratosporus simultaneouslyproduced both PDEase and alkaline phosphatase (APase) at almostequal activity levels under the phosphate-deficient condition.These results suggest that PDE compounds presumably play animportant role as a phosphorus source for PDEase-producing phytoplanktonin coastal environments.     

Nucleotide sequence of the PR-1 gene of Nicotiana tabacum

A gene encoding one of the pathogenesis-related proteins, PR1a, and two related pseudogenes were isolated from Nicotiana tabacum. The cloned PR1a gene (pPR-gamma) and one of the pseudogenes (pPR-alpha) were sequenced and found to have similar structures. The sequence of pPR-gamma was quite similar to that of the cDNA clone of PR1a. The plasmid pPR-gamma did not contain an intron and had a typical promoter sequence in the 5'-flanking region.     

Seasonal changes in vertical distribution, biomass and faecal production of tubificids in the profundal region of a shallow Japanese lake

Two tubificid species Limnodrilus hoffmeisteri and L. claparedeianus formed more than 93% of the total number of oligochaetes in the profundal. Limnodrilus spp. worms were found down to 33 cm in the sediment but in great numbers in the upper zone in June and October. Worms confined to the top 15 cm of sediment accounted for 53-92% of the total number. There were two annual maxima in population density and biomass, one in late spring (66000 inds m⁻², 17 g wet wt m⁻²) and the other in mid autumn (97000 inds m⁻², 176 g wet wt m⁻²). Two regression lines describing the effect of temperature on faecal production rate were obtained; Log F = 0.0604 T (°C) −0.7660 (below 15°C), Log F = 0.0266 T – 0.2170 (above 15°C). In total 26.8 kg dry wt m⁻² of sediment was defecated annually by Limnodrilus spp. The sediment in the 0–10 cm stratum may pass through the guts of the worms 2.3 times a year. Sedimentation rates in profundal region were very low with respect to the faecal production rates of the tubificids.     

Effect of roasting on ochratoxin A level in green coffee beans inoculated with Aspergillus ochraceus

The heat stability of ochratoxin A in green coffee beans inoculated with Aspergillus ochraceus was studied. Heat treatment (roasting) at 200 °C for 10 or 20 min reduced the levels of ochratoxin A by only 0–12% in the dried whole beans. Almost all of the ochratoxin A was infused into the coffee decoction when the roasted samples were ground and extracted with boiling water. Therefore, the reduction of ochratoxin A concentration of contaminated coffee beans by roasting under these conditions is ineffective.     

Identification of a novel nifH-like (frxC) protein in chloroplasts of the liverwort Marchantia polymorpha

The frxC gene, one of the unidentified open reading frames present in liverwort chloroplast DNA, shows significant homology with the nifH genes coding for the Fe protein, a component of the nitrogenase complex (Ohyama et al., 1986, Nature 322: 572–574). A truncated form of the frxC gene was designed to be over-expressed in Escherichia coli and an antibody against this protein was prepared using the purified product as an antigen. This antibody reacted with a protein in the soluble fraction of liverwort chloroplasts, which had an apparent molecular weight of 31 000, as revealed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, in good agreement with a putative molecular weight of 31945 deduced from the DNA sequence of the frxC gene. In a competitive inhibition experiment, the antigenicity of this protein was indicated to be similar to that of the over-expressed protein in E. coli. Therefore, we concluded that the frxC gene was expressed in liverwort chloroplasts and that its product existed in a soluble form. The molecular weight of the frxC protein was approximately 67 000, as estimated by gel filtration chromatography, indicating that the frxC protein may exist as a dimer of two identical polypeptides analogous to the Fe protein of nitrogenase. The results obtained from affinity chromatography supported the possibility that the frxC protein, which possesses a ATP-binding sequence in its N-terminal region that is conserved among various other ATP-binding proteins, has the ability to bind ATP.     

Ca2+ transport through lipid membrane by diastereomer cyclic octapeptides

Effects of the nature and orientation of a side chain in cyclic octapeptides on Ca2+ transport were examined by using cyclo[L-Lys(Z)-Sar-L-Leu-Sar]2 (C8-L), cyclo[L-Lys(Z)-Sar]4 (C8KS), and their diastereomer cyclic octapeptides, cyclo[L-Lys(Z)-Sar-D-Leu-Sar]2 (C8-D) and cyclo[L-Lys(Z)-Sar-D-Lys(Z)-Sar]2 (C8Kk). All these cyclic octapeptides were found to take a single conformation in CDCl3, and the conformation was C2-symmetric for C8-L and C8-D, and C4-symmetric for C8KS and C8Kk. They formed a complex with Ca2+. Upon complexation, C8KS accompanied isomerization of peptide bonds, but C8-D retained the arrangement of peptide bonds. The amount of Ca2+ extracted from an aqueous solution to a chloroform solution by all L cyclic octapeptide C8-L or C8KS was about twice that of Na+, but 6-8-fold smaller than that by C8-D or C8Kk including D units. These cyclic octapeptides were capable of transporting Ca2+ through a lipid membrane above the phase transition temperature, and the transport rate decreased in the order of C8Kk-C8KS greater than C8-D greater than C8-L.     

Sigma receptors in schizophrenic cerebral cortices

Antipsychotics represent high affinity for sigma receptors and sigma-like drugs often have the psychotomimetic properties. Besides, the receptors are unevenly distributed in human brain. These findings suggest that sigma receptors might be involved in the pathophysiology of schizophrenia. Sigma receptors in rat and human brain were measured with [³H]-1, 3, di-o-tolylguanidine (DTG) and non-specific binding of [³H]DTG was determined in the presence of 10^–5M haloperidol. Monovalent and divalent cations strongly inhibited [³H]DTG binding. Glutamate, aspartate and glycine also decreased the binding to human cerebral membranes. With post-mortem brain samples from 12 schizophrenics and 10 controls, sigma receptors were measured in 17 areas of cerebral cortex. Sigma receptors binding showed the regional differences in the cortex, but no significant differences between schizophrenics and controls were observed except the superior parietal cortex where the binding significantly increased in the schizophrenic group. These results suggest that sigma receptors in cerebral cortices might not be directly concerned with the pathophysiological role in schizophrenia.Dedicated to Dr. Morris Aprison. Received too late for publication in special issue.     

Mischarging mutants of Su+2 glutamine tRNA in E. coli. II. Amino acid specificities of the mutant tRNAs

Among the mischarging mutants isolated from strains with Su+2 glutamine tRNA, two double-mutants, A37A29 and A37C38, have been suggested to insert tryptophan at the UAG amber mutation site as determined by the suppression patterns of a set of tester mutants of bacteria and phages (Yamao et al., 1988). In this paper, we screened temperature sensitive mutants of E. coli in which the mischarging suppression was abolished even at the permissive temperature. Four such mutants were obtained and they were identified as the mutants of a structural gene for tryptophanyl-tRNA synthetase (trpS). Authentic trpS mutations, such as trpS5 or trpS18, also restricted the mischarging suppression. These results strongly support the previous prediction that the mutant tRNAs of Su+2, A37A29 and A37C38, are capable of interacting with tryptophanyl-tRNA synthetase and being misaminoacylated with tryptophan in vivo. However, in an assay to determine the specificity of the mutant glutamin tRNAs, we detected predominantly glutamine, but not any other amino acid, being inserted at an amber codon in vivo to any significant degree. We conclude that the mutant tRNAs still accept mostly glutamine, but can accept tryptophan in an extent for mischarging suppression. Since the amber suppressors of Su+7 tryptophan tRNA and the mischarging mutants of Su+3 tyrosine tRNA are charged with glutamine, structural similarity among the tRNAs for glutamine, tryptophan and tyrosine is discussed.     

Inhibition by gossypol of tumor promoter-induced arachidonic acid metabolism in rat peritoneal macrophages

Rat peritoneal macrophages were prelabeled with [3H]arachidonic acid. The release of radioactivity into the medium was increased by treatment with TPA-type tumor promoters, such as TPA, teleocidin and aplysiatoxin, and the non-TPA-type tumor promoter, thapsigargin. Gossypol, at concentrations of 3 and 10 microM, inhibited the release of radioactivity stimulated by both types of tumor promoter, although the mechanism of stimulation of arachidonic acid metabolism is different in the two types of tumor promoter. Stimulation of prostaglandin E2 production by these tumor promoters was also inhibited by treatment with gossypol. Calcium ionophore A23187-stimulated release of radioactivity and prostaglandin E2 production were also inhibited by gossypol treatment. The mechanism of inhibition by gossypol of prostaglandin E2 production is discussed.