Mercury-Induced Inhibition of Photosystem II Activity and Changes in the Emission of Fluorescence from Phycobilisomes in Intact Cells of the Cyanobacterium, Spirulina platensis

Addition of low concentrations of mercury chloride (HgCl₂ tointact cells of the cyanobacterium, Spirulina platensis causedan enhancement in the intensity of fluorescence emitted fromphycocyanin at room temperature and induced blue shifts in theemission peak suggestive of changes in energy transfer withinthe phycobilisomes. HgCl₂ also suppressed the whole-chain electrontransport activity (H₂O methylviologen) at much lower concentrationsthan that required to inhibit Hill activity supported by para-benzoquinone.The extent of inhibition of Hill activity was much higher underhigh-intensity light than that under low-intensity light. Ourresults indicate that mercury ions at low concentrations affectthe transfer of energy within phycobilisomes and at high concentrationsthey inhibit electron transport in this cyanobacterium. (Received February 21, 1989; Accepted October 2, 1989)     

Urea metabolism in the cyanobacterium Anabaena cycadeae: regulation of urea uptake and urease by ammonia

A total of 160 Escherichia coli positive for F165 fimbrial antigen and isolated from diarrheic and septicemic animals, were examined for the presence of the pap, afa, and sfa/foc operons or related nucleotide sequences using colony hybridization. Most isolates shared DNA sequences with the pap operon sequences alone or in association with afa or sfa. Thus, our results indicate that F165-positive E. coli from diseased animals share DNA sequences with operons coding for adhesins important in human extra-intestinal disease and that multiple adhesin systems are often found in single isolates. However, 20% of the F165-positive isolates did not show any homology with the probes representing the three adhesin systems, suggesting that one of the operons responsible for F165 production could be different from the pap, sfa/foc, and afa operons.     

Evidence for the role of intracellular glutamine level in the regulation of glutamine uptake in the cyanobacteriumAnabaena 7120

The role of intracellular glutamine concentration in the regulation of¹⁴C-glutamine uptake was studied in a diazotrophic cyanobacteriumAnabaena 7120. The uptake pattern was found to be biphasic, consisting of a rapid first phase lasting up to 60 s followed by a slower second phase. Azaserine, which could not inhibit in vitro and in vivo glutamine synthetase (GS) activity effectively, inhibited the¹⁴C-glutamine uptake. Glutamine uptake was also not significantly affected when glutamate, methylglutamate, aspartate, arginine, lysine, hydroxylysine, ornithine, and GS inhibitor,L-methionine-DL-sulfoximine (MSX) were simultaneously available during uptake assay, suggesting that glutamine uptake takes place via a general amino acid permease which does not, however, transport basic and acidic amino acids. The azaserine-treated cells had increased and decreased levels of glutamine and glutamate, respectively, suggesting that the increased intracellular glutamine level is responsible for the inhibition of¹⁴C-glutamine uptake and provides evidence here for the role of an intracellular glutamine pool in the regulation of¹⁴C-glutamine uptake inAnabaena 7120.     

Production of cellulase using a mutant strain of Trichoderma reesei growing on lactose in batch culture

The production of cellulases in batch culture was studied using a mutant strain of Trichoderma reesei C-5 growing on lactose. Growth kinetic parameters on 2% lactose were studied and the comparative results for growth and enzyme productivities at two different lactose levels are discussed. The cellulase synthesis rate depended on the lactose concentration in the medium. Although growth was favoured at a higher lactose level, the volumetric enzyme productivity did not increase in proportion and the specific enzyme productivity decreased to a certain extent, indicating that partial catabolic inhibition at higher lactose concentrations may be possible. However, it was noted that the mutant strain was highly depressed and capable of synthesising active cellulases on lactose.     

1α,25-dihydroxy-24-oxo-16-ene vitamin D3, a metabolite of a synthetic vitamin D3 analog, 1α,25-dihydroxy-16-ene vitamin D3, is equipotent to its parent in modulating growth and differentiation of human leukemic cells

1α,25(OH)₂-16-ene-D₃, a synthetic analog of the steroid hormone, 1α,25(OH)₂D₃, has great potential to become a drug in the treatment of leukemia and other proliferative disorders, because of its minimal in vivo calcemic activity associated with a potent inhibitory effect on cell growth. However, at present, the mechanisms through which 1α,25(OH)₂-16-ene-D₃ expresses its biological activities are still not completely understood. Our previous in vitro study in a perfused rat kidney indicated for the first time that 1α,25(OH)₂-16-ene-D₃ and 1α,25(OH)₂D₃ are metabolized differently. 1α,25(OH)₂-24-oxo-16-ene-D₃, an intermediary metabolite of 1α,25(OH)₂-16-ene-D₃ formed through the C-24 oxidation pathway, accumulated significantly in the perfusate when compared to 1α,25(OH)₂-24-oxo-D₃, the corresponding intermediary metabolite of 1α,25(OH)₂D₃. In a subsequent in vivo study, we also reported that 1α,25(OH)₂-24-oxo-16-ene-D₃ exerted immunosuppressive activity equal to its parent, without causing significant hypercalcemia. In order to establish further the critical role of 1α,25(OH)₂-24-oxo-16-ene-D₃, in generating some of the key biological activities ascribed to its parent, we performed the present in vitro study using a human myeloid leukemic cell line (RWLeu-4) as a model. Comparative target tissue metabolism studies indicated that 1α,25(OH)₂-16-ene-D₃ and 1α,25(OH)₂D₃ are metabolized differently in RWLeu-4 cells, and the differences were similar to the ones we previously observed in the rat kidney. The significant finding was the accumulation of 1α,25(OH)₂-24-oxo-16-ene-D₃ in RWLeu-4 cells because of its resistance to further metabolism. Biological activity studies indicated that both 1α,25(OH)₂-16-ene-D₃ and its 24-oxo metabolite produced growth inhibition and promoted differentiation of RWLeu-4 cells to the same extent, and these activities were several fold higher than those exerted by 1α,25(OH)₂D₃. In addition, the genomic action of each vitamin D compound was assessed in a rat osteosarcoma cell line (ROS 17/2.8) by measuring its ability to transactivate a gene construct containing the vitamin D response element of the osteocalcin gene linked to the growth hormone reporter gene. In these studies, both 1α,25(OH)₂-16-ene-D₃ and its 24-oxo metabolite exerted similar but potent transactivation activity which was several fold greater than that exerted by 1α,25(OH)₂D₃ itself. In summary, our results indicate that the production and slow clearance of the bioactive intermediary metabolite, 1α,25(OH)₂-24-oxo-16-ene-D₃, in RWLeu-4 cells contributes significantly to the final expression of the enhanced biological activities ascribed to its parent analog, 1α,25(OH)₂-16-ene-D₃.     

Detection and identification of ferricrocin produced by ectendomycorrhizal fungi in the genusWilcoxina

The ectendomycorrhizal fungiWilcoxina mikolae isolates CSY-14 and RMD-947 andW. rehmii isolate CSY-85 were grown in pure culture under iron-limiting conditions. All three isolates tested positive for siderophore formation using both the ferric perchlorate assay and a sensitive HPLC iron-binding assay. A peptide siderophore was isolated from the culture medium by HPLC and shown to contain the amino acids serine, glycine and ornithine in a 1:2:3 ratio. This siderophore was identified as ferricrocin on the basis of electrospray mass spectroscopy and its co-chromatography in two different HPLC systems with ferricrocin isolated fromAspergillus fumigatus. Ferricrocin was the only siderophore isolated from theseWilcoxina cultures. This is the first report of siderophore formation by ectendomycorrhizal fungi.     

Immunoneutralization of insulin partially modifies dorsoventral patterning in developing frog embryos

Determination of anteroposterior and dorsoventral axes is an important early event in the development of vertebrates involving extensive cellular interactions including inductive events. Recently we showed that insulin plays an essential role in prepancreatic development of the frogMicrohyla ornata. In the present study we have investigated the effects of immunoneutralization of endogenous insulin on the process of pattern formation. Treatment of neurulating embryos with antiserum to insulin caused abnormal pattern formation. The defects included loss of normal architecture of the neural tube, reduction in the size of the neural tube and, most conspicuously, rotation of the dorsoventral axis of the neural tube, notochord and adjoining mesodermal elements. The effects could be alleviated partially by pretreatment of embryos with exogenous insulin. This supports our belief that insulin plays an important role in induction and pattern formation of the amphibian nervous system. In addition, using 2-deoxy-α-D-glucose, an inhibitor of glucose metabolism, it is shown that the stimulatory effects of exogenous insulin on developing frog embryos are, at least partially, through the glucose metabolism pathway. Preliminary results of this study were presented at the National Symposium on Genes and Human Environment, held at Hyderabad, February 1994 and DAE Symposium on Stress and Adaptive Responses in Biological Systems, held at Vadodara, March 1994.     

Physical characteristics of bone composite materials

To study the effects of varying mineral content and various trace elements in bone composities on its electrical behavior and possible use in design of transducers, various physical, dielectric, piezoelectric, and electromechanical parameters have been measured. For electrical characterization of various such composites in the high-frequency region (1–108 MHz), variation of impedance (Z), phase angle (tan ), and relative output voltage with frequency has been examined. Furtherfore, the Curie temperature has been determined and the temperature variation of capacitance and loss factor (tan ) studied (24–225°C). Two types of bone composites were prepared and studied. First, powdered collagen and apatite obtained from full bone were mixed intimately in various proportions by weight to prepare eleven bone compositions. Second, such bone materials were made to contain 5–10% various doping foreign additives (A1Br₃, Na₂CO₃, SrCO₃, LiCO₃, Sb₂O₃, ZnO, Nb₂O₅, piezoelectric ceramic (PZT), and Pb(NO₃)₂. It has been observed that a bone composition of 50% collagen + 50% apatite has possible piezoelectric application and other compositions [85% collagen + 15% apatite, 90% collagen + 10% ZnO, and 90% bone + 10% Ba(OH)₂] have a sharp rise in capacitance near the Curie temperature. The Curie temperature is generally shifted towards higher values by additives. It is expected that such results will be relevant in characterizing bone behavior.     

Interaction of the carboxamide of NADPH with Lactobacillus casei dihydrofolate reductase

Dihydrofolate reductase from Lactobacillus casei and its complexes with NADPH and methotrexate yield well-resolved Raman spectra. The 1685-cm^?1 Raman band assigned to the carboxamide of NADPH persists in the NADPH-enzyme binary complex but is absent from the NADPH-methotrexate-enzyme ternary complex. This is ascribed to stabilization of the polarized form of the carboxamide by H bonding to the NH and CO groups of Ala 6 and Ile 13 of the peptide backbone.