Methyl mercury uptake by free and immobilized cyanobacterium

Methyl mercury uptake in free cells and different immobilizates of the cyanobacteriumNostoc calcicola has been examined. The general growth of the immobilized cyanobacterial cells could be negatively correlated with methyl mercury uptake. Alginate spheres proved most efficient in terms of uptake rate (0.48 nmol mg protein^–1 min^–1, 10 min) and total bioaccumulation (10.71 nmol mg protein^–1, 1 h) with a bioconcentration factor of 3.3×10³. Alginate biofilms showed a faster methyl mercury accumulation rate (0.83 nmol mg protein^–1 min^–1, 10 min) with a saturation of 10.28 nmol mg protein^–1 reached within only 30 min (bioconcentration factor, 3.1×10³). Foam preparations with a slow initial uptake approximated biofilms but were characterized by a lower bioconcentration factor (2.8×10³). Free cells, in comparison, maintained the initial slow rate of uptake (0.62 nmol mg protein^–1 min^–1, 10 min), saturating at 30 min (8.81 nmol mg protein^–1), and the resultant lowest bioconcentration factor (2.7×10³). Cell ageing (30 days) brought a drastic reduction (3-fold) in organomercury uptake by free cells while alginate spheres maintained the same potential. Foam preparations of the same age showed a significant improvement in methyl mercury uptake followed by only a marginal decline in alginate biofilms. Data are discussed in the light of the physiological efficiency and longevity of immobilized cells.     

Formation of acetic acid from cellulosic substrates byFusarium oxysporum

Summary Four strains of Fusarium oxysporum and a strain of Monilia brunnae were screened for their ability to convert cellulosic substrates into ethanol/acetic acid. These strains were found to utilize cellulose and produce extracellular cellulases. However, only F. oxysporum 841 was found to convert glucose, xylose, and cellulose into ethanol and acetic acid as major end-products under microaerobic conditions. Acetic acid at a level of 4.7 g/l resulted in a single-step process on potato pulp medium, indicating the potential of the strain for converting cellulosic substrates into acetic acid. Offprint requests to: K. Schügerl     

Insulin-stimulated tyrosine phosphorylation of a 43 kDa protein in rat liver membranes

The insulin receptor (IR) tyrosine kinase is essential for the regulation of different cellular functions by insulin. This may occur by a direct phosphorylation of membrane and/or cytoplasmic proteins by the IR tyrosine kinase. Hence it is important to identify putative physiological substrates for the IR tyrosine kinase. In this study we found that the glycoprotein fraction from rat liver membranes contain a 43 kDa protein (pp43) which, like the -subunit of IR, is phosphorylated in an insulin-dependent manner. A 25-fold enhancement of ³²P incorporation into pp43 by insulin was found under optimal conditions. Half-maximal phosphorylation of pp43 and the -subunit of IR were attained at 66 nM and 60 nM insulin, respectively. Mn²⁺ (K_a = 1.0 mM) was much better than Mg²⁺ (K_a = 6.3 mM) in supporting pp43 phosphorylation. Insulin-stimulated phosphorylation of pp43 (t_1/2 = 3.6 min) proceeded at a much slower rate compared to that of the -subunit of IR (t_1/2 = 1.2 min). Phosphoamino acid analysis of pp43 revealed that both tyrosine and serine are phosphorylated in the ratio 4 : 1. Tyrosine, but not serine, phosphorylation was increased 12-fold by insulin. Phosphorylation of pp43 occurred on 4 major tryptic peptides. Comparison to the tryptic phosphopeptides from IR -subunit suggest that pp43 was not derived from IR -subunit by proteolysis. Our results suggest that pp43 may be an endogenous substrate for the IR tyrosine kinase.     

Effect of ciprofibrate on the activation and oxidation of very long chain fatty acids

The effect of ciprofibrate, a hypolipidemic drug, was examined in the metabolism of palmitic (C_16:0) and lignoceric (C_24:0) acids in rat liver. Ciprofibrate is a peroxisomal proliferating drug which increases the number of peroxisomes. The palmitoyl-CoA ligase activity in peroxisomes, mitochondria and microsomes from ciprofibrate treated liver was 3.2, 1.9 and 1.5-fold higher respectively and the activity for oxidation of palmitic acid in peroxisomes and mitochondria was 8.5 and 2.3-fold higher respectively. Similarly, ciprofibrate had a higher effect on the metabolism of lignoceric acid. Treatment with ciprofibrate increased lignoceroyl-CoA ligase activity in peroxisomes, mitochondria and microsomes by 5.3, 3.3 and 2.3-fold respectively and that of oxidation of lignoceric acid was increased in peroxisomes and mitochondria by 13.4 and 2.3-fold respectively. The peroxisomal rates of oxidation of palmitic acid (8.5-fold) and lignoceric acid (13.4-fold) were increased to a different degree by ciprofibrate treatment. This differential effect of ciprofibrate suggests that different enzymes may be responsible for the oxidation of fatty acids of different chain length, at least at one or more step(s) of the peroxisomal fatty acid -oxidation pathway.     

Onychomycosis caused by Scopulariopsis brumptii

Scopulariopsis brumptii was isolated from nail lesions in left hand of a 42 year-old-farmer. The direct microscopic examination of the nail samples revealed light brown, septate, branched fungal hyphae along with thick-walled spherical cells. The histopathological examination showed involvement of internal phase of the nail plate. Amongst the antimycotics tested against S. brumptii In vitro oxiconazole was found to be the most active with MIC value of 10 g/ml^–1. This report documents the first instance of onychomycosis caused by S. brumptii.     

A sequence motif found in a Drosophila heterochromatin protein is conserved in animals and plants.

Modifiers of position-effect-variegation in Drosophila encode proteins that are thought to modify chromatin, rendering it heritably changed in its expressibility. In an attempt to identify similar modifier genes in other species we have utilized a known sequence homology, termed chromo box, between a suppressor of position-effect-variegation, Heterochromatin protein 1 (HP1), and a repressor of homeotic genes, Polycomb (Pc). A PCR generated probe encompassing the HP1 chromo box was used to clone full-length murine cDNAs that contain conserved chromo box motifs. Sequence comparisons, in situ hybridization experiments, and RNA Northern blot analysis suggest that the murine and human sequences presented in this report are homologues of the Drosophila HP1 gene. Chromo box sequences can also be detected in other animal species, and in plants, predicting a strongly conserved structural role for the peptide encoded by this sequence. We propose that epigenetic (yet heritable) changes in gene expressibility, characteristic of chromosomal imprinting phenomena, can largely be explained by the action of such modifier genes. The evolutionary conservation of the chromo box motif now enables the isolation and study of putative modifier genes in those animal and plant species where chromosomal imprinting has been described.     

Regression of human melanoma xenografts in nude mice injected with methotrexate linked to monoclonal antibody 225.28 to human high molecular weight-melanoma associated antigen

Summary Intravenous injections into nude mice of 5 mg/kg methotrexate (MTX) linked to the antibody to human high molecular weight-melanoma associated antigen (HMW-MAA), monoclonal antibody (mAb) 225.28, an IgG_2a, on days 1, 4, 7, 10 and 14, starting 24 h after subcutaneous inoculation of 2 × 10⁶ cultured human M21 melanoma cells inhibited mean tumor volume by 90% on day 14 and by 65% on day 50 after the beginning of the treatment. Injections of equimolar amounts of free MTX and MTX linked to normal mouse IgG or to an isotypematched myeloma protein did not inhibit tumor growth significantly. MTX linked to mAb 225.28 did not inhibit the xenograft of a subline of human melanoma cell line M21 without detectable expression of HMW-MAA. In a clonogenic assay, the MTX-225.28 conjugate was three times more potent in inhibiting the growth of M21 melanoma cells than free MTX, but did not inhibit the growth of kidney carcinoma cells Caki-1, which do not express high-M _r MAA. In contrast, MTX linked to the mAb DAL K29, reacting with kidney carcinoma cells Caki-1, inhibited their growth but did not affect that of melanoma cells. M21 melanoma cells isolated from the residual tumor of a mouse treated with the MTX-225.28 conjugate did not differ in their reactivity with mAb 225.28 and in their sensitivity to MTX when compared with M21 cells from an untreated mouse.     

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.     

Assay of acetohydroxyacid synthase

Acetohydroxyacid synthase (AHAS), also known as acetolactate synthase, has received attention recently because of the finding that it is the site of action of several new herbicides. The most commonly used assay for detecting the enzyme is spectrophotometric involving an indirect detection of the product acetolactate. The assay involves the conversion of the end product acetolactate to acetoin and the detection of acetoin via the formation of a creatine and naphthol complex. There is considerable variability in the literature as to the details of this assay. We have investigated a number of factors involved in detecting AHAS in crude ammonium sulfate precipitates using this spectrophotometric method. Substrate and cofactor saturation levels, pH optimum, and temperature optimum have been determined. We have also optimized a number of factors involved in the generation and the detection of acetoin from acetolactate. The results of these experiments can serve as a reference for new investigators in the study of AHAS.